fix(plex): subtitles stop blocking the request, and stop re-reading the file
Bug hunt 2026-09, items 8 and 12 — the two things the Plex player was measurably
lying about.
Item 8: picking a subtitle track showed nothing for a long time, and the reported
workaround was to stop/start until it suddenly worked. Measured on prod against a
17.06 GB MKV with two embedded SubRip tracks:
full pass, one track 154 s
full pass, both tracks in ONE run 111 s
-c:s copy (no WebVTT conversion) 143 s
from 1:00:00 to the end of file 66 s
a 630 s window at 1:00:00, both 8 s
So the conversion was never the cost: ffmpeg streams every byte of the container
between its seek point and its stop point, and the array delivers ~140 MB/s. The
only lever is reading less. Three changes follow from that:
* a window around the playhead is extracted and published FIRST (seconds), and
the full pass completes behind it;
* every embedded text track rides that same single read — picking Hungarian used
to cost a full pass and then switching to English cost another one;
* none of it happens inside a request any more. The endpoint answers 202 while a
background worker extracts, the player polls /status (carrying its position, so
the window follows the viewer), and one ffmpeg run finally has a timeout.
-copyts is deliberately absent from a windowed pass: with it ffmpeg ignores -t and
reads the whole container anyway (measured — a [0, 600 s] window still took the
full 145 s), so a window comes back on a zero-based clock and is shifted to
absolute time here. Cached tracks written by older builds have no coverage sidecar
and count as complete, so nothing is re-extracted after the upgrade.
The <track> is no longer mounted before the server has something to put in it; a
"Preparing subtitles: …" notice stands in, and a track that can never be shown says
why instead of leaving the viewer to conclude the picker does nothing.
Item 12: "Bitrate" read a constant 211 kbps on every remux, because it was the
master playlist's BANDWIDTH — which ffmpeg derives from the one stream whose rate
it knows, the -b:a 192k AAC track, plus 10%. It is a measurement now: bytes per
second of MEDIA from hls.js FRAG_LOADED, accumulated per fragment type and summed
(a multi-audio session's video and audio renditions cover the same media seconds,
so pooling them would report half the truth), and an honest dash until the first
fragment lands. The panel also finally names the audio and subtitle track in play.
Verified in the browser against the real Plex library, and every new test
mutation-checked.
This commit is contained in:
@@ -1,15 +1,57 @@
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"""WebVTT conversion, HLS-clock time-shift, and on-disk cache for Plex subtitle streams.
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"""WebVTT conversion, HLS-clock time-shift, and the on-disk cache + background extractor for Plex
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subtitle streams.
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Text subtitles (embedded or external) are turned into WebVTT so the browser <track> can render them;
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bitmap subtitles (Blu-ray/DVD) can't be (would need burn-in). Converted VTTs are cached on the shared
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Plex on-disk cache root (``cache.CACHE_DIR``).
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WHY THERE IS A BACKGROUND EXTRACTOR HERE — measured on prod, 2026-09-10, against a 17.06 GB 1080p
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MKV with two embedded SubRip tracks on the 81 TB array:
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=========================================================== ========
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full pass, ONE track (what this module used to do) 154 s
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full pass, BOTH text tracks in a SINGLE ffmpeg run 111 s
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`-c:s copy` instead of converting to WebVTT 143 s
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from 1:00:00 to the end of the file 66 s
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a 630 s WINDOW at 1:00:00, both tracks 8 s
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=========================================================== ========
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The conversion is not the cost (dropping it saved 7%): ffmpeg has to stream every byte of the
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container between its seek point and its stop point, and the array delivers ~140 MB/s — so the time
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is (bytes read) / 140 MB/s, and the ONLY lever is reading less. Hence:
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* extract a WINDOW around the playhead first — the viewer sees subtitles in seconds — then complete
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the whole track in the background so every later seek is instant and the next session is free;
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* extract EVERY embedded text track in ONE pass, because the read is shared: picking Hungarian used
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to cost a full read and then switching to English cost another one (the "hektikus" report);
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* never do any of it inside a request (it froze the <track> with no feedback AND held an API worker
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thread for the whole read).
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`-copyts` CANNOT be used for a window: it makes ffmpeg ignore `-t`/`-to` (measured — a [0, 600 s]
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window still took the full 145 s and emitted the whole track), so windows are extracted on a
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zero-based clock and shifted back to absolute time here with `shift_vtt`.
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"""
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import json
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import logging
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import re
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import subprocess
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import tempfile
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import threading
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import time
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from concurrent.futures import ThreadPoolExecutor
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from pathlib import Path
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from sqlalchemy.orm import Session
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from app.db import SessionLocal
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from app.models import PlexItem
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from app.plex import paths as plex_paths
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from app.plex.cache import CACHE_DIR
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from app.plex.client import PlexError
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from app.plex.client import PlexClient, PlexError
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from app.plex.lookups import by_rating_key
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log = logging.getLogger("siftlode.plex")
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# Image-based subtitle codecs (Blu-ray/DVD) — can't be turned into text WebVTT (would need burn-in).
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BITMAP_SUBS = {
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@@ -109,7 +151,7 @@ def ffmpeg_to_vtt(src: str, sub_ord: int | None) -> str:
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"webvtt",
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"pipe:1",
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]
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r = subprocess.run(cmd, capture_output=True)
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r = subprocess.run(cmd, capture_output=True, timeout=EXTRACT_TIMEOUT_S)
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if r.returncode != 0 or not r.stdout:
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raise PlexError(
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(r.stderr or b"").decode("utf-8", "replace")[:200] or "ffmpeg subtitle convert failed"
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@@ -133,3 +175,329 @@ def cache_write(key: str, vtt: str) -> None:
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tmp.replace(CACHE_DIR / f"{key}.vtt") # atomic publish
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except OSError:
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pass
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# --- cache identity -----------------------------------------------------------------------------
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# The cached VTT holds ABSOLUTE cue times (per rating_key + subtitle ordinal); the per-session shift
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# is applied on the way out, so a resume/seek to any offset reuses the same file. Beside it, a small
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# JSON sidecar records WHICH absolute-time ranges the file actually covers — a windowed extraction
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# publishes a usable but incomplete track, and "incomplete" must never be mistaken for "all there is".
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_FULL_END_S = 1_000_000_000.0 # stand-in for "to the end of the file" (JSON can't hold infinity)
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def cache_key(rating_key: str, sub_ord: int) -> str:
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return f"sub_{rating_key}_{sub_ord}"
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def _vtt_path(key: str) -> Path:
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return CACHE_DIR / f"{key}.vtt"
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def _meta_path(key: str) -> Path:
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return CACHE_DIR / f"{key}.json"
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def read_meta(key: str) -> tuple[list[list[float]], bool]:
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"""Covered absolute-time ranges + whether the track is fully extracted. A VTT with no sidecar
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(written by an older build, which only ever cached complete tracks) counts as complete."""
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try:
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raw = json.loads(_meta_path(key).read_text(encoding="utf-8"))
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return [[float(a), float(b)] for a, b in raw.get("ranges", [])], bool(raw.get("complete"))
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except (OSError, ValueError, TypeError):
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return ([[0.0, _FULL_END_S]], True) if _vtt_path(key).exists() else ([], False)
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def _write_meta(key: str, ranges: list[list[float]], complete: bool) -> None:
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try:
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CACHE_DIR.mkdir(parents=True, exist_ok=True)
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tmp = CACHE_DIR / f"{key}.json.tmp"
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tmp.write_text(json.dumps({"ranges": ranges, "complete": complete}), encoding="utf-8")
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tmp.replace(_meta_path(key))
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except OSError:
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pass
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def generation(key: str) -> int:
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"""Monotonic id of the cached file's current content. It goes into the <track> URL so that when a
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window is superseded by a wider one the browser refetches instead of keeping the short VTT."""
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try:
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return _vtt_path(key).stat().st_mtime_ns
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except OSError:
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return 0
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def merge_ranges(ranges: list[list[float]]) -> list[list[float]]:
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"""Sort + coalesce touching/overlapping covered ranges."""
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out: list[list[float]] = []
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for a, b in sorted((r for r in ranges if r[1] > r[0]), key=lambda r: r[0]):
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if out and a <= out[-1][1]:
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out[-1][1] = max(out[-1][1], b)
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else:
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out.append([a, b])
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return out
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def covers(ranges: list[list[float]], at: float) -> bool:
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return any(a <= at <= b for a, b in ranges)
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def merge_vtt(*sources: str) -> str:
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"""Union of the cue blocks of several absolute-time VTTs, ordered by start time.
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Two extraction passes over the same file emit identical cues for the region they share, so
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de-duplication keys off the TIMING line — the one part of a cue that identifies it uniquely and
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that neither pass can renumber (ffmpeg's webvtt muxer writes no cue identifiers)."""
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seen: set[str] = set()
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cues: list[tuple[float, str]] = []
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for src in sources:
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for block in re.split(r"\n[ \t]*\n", src or ""):
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b = block.strip()
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if not b or "-->" not in b:
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continue # header / NOTE / STYLE — the merged file gets its own single header
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timing = next(ln for ln in b.split("\n") if "-->" in ln)
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if timing in seen:
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continue
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seen.add(timing)
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try:
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start = _vtt_ts_to_s(timing.partition("-->")[0].strip())
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except (ValueError, IndexError):
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continue
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cues.append((start, b))
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cues.sort(key=lambda c: c[0])
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return "WEBVTT\n\n" + "\n\n".join(b for _, b in cues) + "\n"
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def publish(key: str, vtt: str, covered: tuple[float, float], complete: bool) -> None:
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"""Merge a freshly extracted region into the cached track and widen its covered ranges."""
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old = cache_read(key)
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old_ranges, was_complete = read_meta(key)
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cache_write(key, merge_vtt(old or "", vtt))
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_write_meta(key, merge_ranges(old_ranges + [list(covered)]), complete or was_complete)
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# --- background extraction ----------------------------------------------------------------------
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# How much of the track to extract before the viewer sees anything. WINDOW_PRE_S starts a little
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# before the playhead so a cue that is already on screen is not missed; WINDOW_LEN_S is the span
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# published as the first, provisional VTT (~4 s of work on the measured file). It only has to hold
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# until the full pass lands behind it — 111 s for that file — so it is deliberately much longer than
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# any realistic full pass.
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WINDOW_PRE_S = 30.0
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WINDOW_LEN_S = 300.0
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# Ceiling on one ffmpeg run so a wedged extraction can't hold a pool thread forever (the old
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# in-request extraction had no timeout at all).
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EXTRACT_TIMEOUT_S = 900.0
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# A failed track is remembered briefly so a 1 s status poll doesn't respawn ffmpeg every second, and
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# forgotten again soon after so fixing the file (or Plex coming back) doesn't need a restart.
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FAIL_TTL_S = 60.0
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# Two items' full passes plus a window for a third: enough that a seek into an un-extracted region is
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# served while a full pass runs, bounded so a burst can't thrash the array.
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_POOL = ThreadPoolExecutor(max_workers=3, thread_name_prefix="plex-subs")
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_LOCK = threading.Lock()
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_INFLIGHT: set[tuple] = set()
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_FAILURES: dict[str, tuple[str, float]] = {}
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class SubtitleUnavailable(Exception):
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"""A track that cannot be served as text, carrying the stable code the route maps to a status."""
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def __init__(self, code: str):
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super().__init__(code)
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self.code = code
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# code -> HTTP status. An extraction/upstream failure is 422 with a structured detail (502 is
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# reserved for the raw byte proxies); the rest are genuine "no such thing" / "not text".
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UNAVAILABLE_STATUS = {
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"no_item": 404,
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"no_track": 404,
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"no_file": 404,
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"not_fetchable": 404,
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"bitmap": 415,
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"extract_failed": 422,
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"plex_error": 422,
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}
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def reset_state() -> None:
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"""Drop the in-flight/failure registries (tests; nothing in the app needs it)."""
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with _LOCK:
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_INFLIGHT.clear()
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_FAILURES.clear()
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def _fail(key: str, code: str) -> None:
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with _LOCK:
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_FAILURES[key] = (code, time.monotonic())
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def _recent_failure(key: str) -> str | None:
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with _LOCK:
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hit = _FAILURES.get(key)
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if hit and time.monotonic() - hit[1] < FAIL_TTL_S:
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return hit[0]
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_FAILURES.pop(key, None)
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return None
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def ensure(rating_key: str, sub_ord: int, at: float = 0.0) -> dict:
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"""State of one subtitle track, scheduling whatever extraction is still missing. NEVER blocks.
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``ready`` = fully extracted · ``partial`` = usable, covers ``at``, still growing · ``preparing``
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= nothing to show for ``at`` yet · ``failed`` = ``code`` says why. ``gen`` changes whenever the
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cached file grows, so the client can refetch a window that has been superseded."""
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key = cache_key(rating_key, sub_ord)
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ranges, complete = read_meta(key)
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have = cache_read(key) is not None
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covered = have and covers(ranges, at)
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if complete and have:
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return {"state": "ready", "code": None, "gen": generation(key)}
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code = _recent_failure(key)
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if code and not covered:
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return {"state": "failed", "code": code, "gen": generation(key)}
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if not code:
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_schedule(rating_key, sub_ord, at, want_window=not covered)
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return {"state": "partial" if covered else "preparing", "code": None, "gen": generation(key)}
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def _schedule(rating_key: str, sub_ord: int, at: float, want_window: bool) -> None:
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"""Kick off the jobs this track still needs: the window that makes it watchable now, and the one
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full pass that makes it complete. Each is deduplicated by identity, so a 1 s status poll (or a
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second viewer) joins the running job instead of starting another ffmpeg."""
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jobs: list[tuple[tuple, float | None]] = []
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if want_window:
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w_start = max(0.0, at - WINDOW_PRE_S)
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jobs.append((("win", rating_key, round(w_start)), w_start))
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jobs.append((("full", rating_key), None))
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for ident, window_start in jobs:
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with _LOCK:
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if ident in _INFLIGHT:
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continue
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_INFLIGHT.add(ident)
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_POOL.submit(_run, ident, rating_key, sub_ord, window_start)
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def _run(ident: tuple, rating_key: str, sub_ord: int, window_start: float | None) -> None:
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try:
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_extract_and_publish(rating_key, sub_ord, window_start)
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except SubtitleUnavailable as e:
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_fail(cache_key(rating_key, sub_ord), e.code)
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except PlexError as e:
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log.warning("subtitle extraction failed for %s/%s: %s", rating_key, sub_ord, e)
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_fail(cache_key(rating_key, sub_ord), "plex_error")
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except (
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Exception
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): # a worker thread has nobody to raise to — record it, let the next poll see it
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log.exception("subtitle extraction crashed for %s/%s", rating_key, sub_ord)
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_fail(cache_key(rating_key, sub_ord), "extract_failed")
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finally:
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with _LOCK:
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_INFLIGHT.discard(ident)
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def _text_streams(db: Session, rating_key: str) -> tuple[PlexItem, list[dict]]:
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"""The item plus its subtitle streams, in the ordinal order the API and the UI both use."""
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it = by_rating_key(db, PlexItem, rating_key)
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if it is None:
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raise SubtitleUnavailable("no_item")
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with PlexClient(db) as plex:
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part = ((plex.metadata(it.rating_key) or {}).get("Media") or [{}])[0].get("Part") or [{}]
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return it, [s for s in (part[0].get("Stream") or []) if s.get("streamType") == 3]
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def _is_bitmap(stream: dict) -> bool:
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return (stream.get("codec") or stream.get("format") or "").lower() in BITMAP_SUBS
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def _extract_and_publish(rating_key: str, sub_ord: int, window_start: float | None) -> None:
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"""One extraction job. A sidecar track is fetched whole from Plex (cheap, no ffmpeg); an embedded
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one is extracted together with EVERY other embedded text track in the file, because they all ride
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on the same single read — the whole point of the measurement at the top of this module."""
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with SessionLocal() as db:
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it, subs = _text_streams(db, rating_key)
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if sub_ord < 0 or sub_ord >= len(subs):
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raise SubtitleUnavailable("no_track")
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want = subs[sub_ord]
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if _is_bitmap(want):
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raise SubtitleUnavailable("bitmap")
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if want.get("key"): # external sidecar → one fetch, always the complete track
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if window_start is not None:
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return # nothing to window — the full job serves it in a single fetch
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vtt = _sidecar_vtt(db, want)
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publish(cache_key(rating_key, sub_ord), vtt, (0.0, _FULL_END_S), True)
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return
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if want.get("index") is None:
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raise SubtitleUnavailable("not_fetchable")
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src = plex_paths.local_media_path(db, it.file_path)
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if src is None:
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raise SubtitleUnavailable("no_file")
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# Ordinal among the file's EMBEDDED subtitle streams — what `-map 0:s:N` counts. Sidecars sit
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# in the same list but not in the file, so they must not shift the mapping.
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targets = {
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sum(1 for x in subs[:i] if x.get("index") is not None): i
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for i, s in enumerate(subs)
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if s.get("index") is not None and not _is_bitmap(s)
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}
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start = window_start or 0.0
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length = (WINDOW_LEN_S + WINDOW_PRE_S) if window_start is not None else None
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end = _FULL_END_S if length is None else start + length
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for emb_ord, vtt in _ffmpeg_extract(str(src), sorted(targets), window_start, length).items():
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publish(
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cache_key(rating_key, targets[emb_ord]),
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shift_vtt(vtt, -start), # zero-based window clock → absolute cue times
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(start, end),
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length is None,
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)
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def _sidecar_vtt(db: Session, stream: dict) -> str:
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"""An external subtitle file, fetched through Plex and converted to WebVTT."""
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with PlexClient(db) as plex:
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raw = plex.raw_get(stream["key"])
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codec = (stream.get("codec") or stream.get("format") or "").lower()
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if codec in ("srt", "subrip", ""):
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return srt_to_vtt(raw.decode("utf-8", "replace"))
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with tempfile.NamedTemporaryFile(suffix="." + (codec or "sub"), delete=False) as fh:
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fh.write(raw)
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tmp = fh.name
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try:
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return ffmpeg_to_vtt(tmp, None)
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finally:
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Path(tmp).unlink(missing_ok=True)
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def _ffmpeg_extract(
|
||||
src: str, emb_ords: list[int], start: float | None, length: float | None
|
||||
) -> dict[int, str]:
|
||||
"""Extract several embedded subtitle streams to WebVTT in ONE ffmpeg run (= one read of the file).
|
||||
|
||||
`start`/`length` bound the read to a window. Without `-copyts` the cues come out on a zero-based
|
||||
clock (the caller shifts them back) — which is exactly why `-copyts` is absent: with it ffmpeg
|
||||
ignores `-t` and reads the whole container anyway (measured)."""
|
||||
if not emb_ords:
|
||||
return {}
|
||||
with tempfile.TemporaryDirectory(prefix="plexsub-") as tmpdir:
|
||||
cmd = ["ffmpeg", "-nostdin", "-loglevel", "error"]
|
||||
if start:
|
||||
cmd += ["-ss", f"{start:.3f}"]
|
||||
cmd += ["-i", src]
|
||||
outs = {o: Path(tmpdir) / f"{o}.vtt" for o in emb_ords}
|
||||
for emb_ord, out in outs.items():
|
||||
cmd += ["-map", f"0:s:{emb_ord}"]
|
||||
if length is not None:
|
||||
cmd += ["-t", f"{length:.3f}"]
|
||||
cmd += ["-f", "webvtt", "-y", str(out)]
|
||||
r = subprocess.run(cmd, capture_output=True, timeout=EXTRACT_TIMEOUT_S)
|
||||
got = {
|
||||
o: p.read_text(encoding="utf-8", errors="replace")
|
||||
for o, p in outs.items()
|
||||
if p.exists()
|
||||
}
|
||||
if not got:
|
||||
raise SubtitleUnavailable("extract_failed")
|
||||
if r.returncode != 0:
|
||||
# Partial output with a non-zero exit still beats nothing (a later pass widens it) — say so.
|
||||
log.warning("ffmpeg subtitle pass exited %s: %s", r.returncode, (r.stderr or b"")[:200])
|
||||
return got
|
||||
|
||||
@@ -1,8 +1,6 @@
|
||||
"""Plex playback: image/subtitle proxies, HLS streaming, and watch-state writes."""
|
||||
|
||||
import hashlib
|
||||
import os
|
||||
import tempfile
|
||||
import threading
|
||||
from datetime import datetime, timedelta, timezone
|
||||
|
||||
@@ -89,62 +87,45 @@ def image(rating_key: str, request: Request, variant: str = "thumb") -> Response
|
||||
return imgcache.response(data, ct)
|
||||
|
||||
|
||||
@router.get("/subtitle/{rating_key}/{sub_ord}/status")
|
||||
def subtitle_status(rating_key: str, sub_ord: int, request: Request, at: float = 0.0) -> dict:
|
||||
"""Is this subtitle track showable yet — and if not, get it moving. Extraction runs in the
|
||||
background (see plex/subtitles.py for the measurements that forced it there), so the player polls
|
||||
this while it waits instead of hanging on a <track> that will not load for a minute or more.
|
||||
|
||||
`at` is the viewer's absolute position: the extractor windows around it, so what gets read first
|
||||
is the part actually about to be watched."""
|
||||
_require_session(request)
|
||||
return subtitles.ensure(rating_key, sub_ord, at)
|
||||
|
||||
|
||||
@router.get("/subtitle/{rating_key}/{sub_ord}")
|
||||
def subtitle(rating_key: str, sub_ord: int, request: Request, offset: float = 0.0) -> Response:
|
||||
def subtitle(
|
||||
rating_key: str, sub_ord: int, request: Request, offset: float = 0.0, at: float = 0.0
|
||||
) -> Response:
|
||||
"""Serve the ord-th subtitle track as WebVTT for the browser's <track> — so choosing a subtitle
|
||||
overlays it directly (no HLS re-mux / session restart). Handles EXTERNAL sidecar subs (fetched
|
||||
from Plex via the stream `key` — the old `-map 0:s` broke on these since they're not in the file)
|
||||
AND embedded text subs (extracted from the local file). Image subs (PGS/VobSub) → 415. Disk-cached."""
|
||||
AND embedded text subs (extracted from the local file). Image subs (PGS/VobSub) → 415. Disk-cached.
|
||||
|
||||
NEVER extracts inline. A cold track answers 202 and the extraction proceeds in the background; the
|
||||
player mounts the <track> only once /status says there is something to show, so in practice this
|
||||
is only ever hit warm (or on a cache eviction race, which the 202 sends back to polling)."""
|
||||
_require_session(request)
|
||||
# Cache the ABSOLUTE-time VTT once (per rk+ord); the per-session cue-shift is applied on the way
|
||||
# out, so a resume/seek to any offset reuses the same cached track (no cache-per-offset explosion).
|
||||
cache_key = f"sub_{rating_key}_{sub_ord}"
|
||||
hit = subtitles.cache_read(cache_key)
|
||||
if hit is not None:
|
||||
return Response(subtitles.shift_vtt(hit, offset), media_type="text/vtt")
|
||||
try:
|
||||
with SessionLocal() as db:
|
||||
it = item_or_404(db, rating_key)
|
||||
with PlexClient(db) as plex:
|
||||
part = ((plex.metadata(it.rating_key) or {}).get("Media") or [{}])[0].get(
|
||||
"Part"
|
||||
) or [{}]
|
||||
subs = [s for s in (part[0].get("Stream") or []) if s.get("streamType") == 3]
|
||||
if sub_ord < 0 or sub_ord >= len(subs):
|
||||
raise HTTPException(status_code=404, detail="No such subtitle")
|
||||
s = subs[sub_ord]
|
||||
codec = (s.get("codec") or s.get("format") or "").lower()
|
||||
if codec in subtitles.BITMAP_SUBS:
|
||||
raise HTTPException(
|
||||
status_code=415,
|
||||
detail="Image-based subtitle can't be shown as text",
|
||||
)
|
||||
if s.get("key"): # external sidecar → fetch from Plex, convert to VTT
|
||||
raw = plex.raw_get(s["key"])
|
||||
if codec in ("srt", "subrip", ""):
|
||||
vtt = subtitles.srt_to_vtt(raw.decode("utf-8", "replace"))
|
||||
else:
|
||||
fd, tmp = tempfile.mkstemp(suffix="." + (codec or "sub"))
|
||||
try:
|
||||
os.write(fd, raw)
|
||||
os.close(fd)
|
||||
vtt = subtitles.ffmpeg_to_vtt(tmp, None)
|
||||
finally:
|
||||
os.unlink(tmp)
|
||||
elif s.get("index") is not None: # embedded → extract from the local file
|
||||
src = plex_paths.local_media_path(db, it.file_path)
|
||||
if src is None:
|
||||
raise HTTPException(status_code=404, detail="Media file not found on disk")
|
||||
emb_ord = sum(1 for x in subs[:sub_ord] if x.get("index") is not None)
|
||||
vtt = subtitles.ffmpeg_to_vtt(str(src), emb_ord)
|
||||
else:
|
||||
raise HTTPException(status_code=404, detail="Subtitle not fetchable")
|
||||
except PlexNotConfigured as e:
|
||||
raise HTTPException(status_code=400, detail=str(e))
|
||||
except PlexError as e:
|
||||
raise HTTPException(status_code=502, detail=f"Subtitle fetch failed: {e}")
|
||||
subtitles.cache_write(cache_key, vtt)
|
||||
return Response(subtitles.shift_vtt(vtt, offset), media_type="text/vtt")
|
||||
# The cached VTT holds ABSOLUTE cue times (per rk+ord); the per-session cue-shift is applied on
|
||||
# the way out, so a resume/seek to any offset reuses the same track (no cache-per-offset explosion).
|
||||
st = subtitles.ensure(rating_key, sub_ord, at)
|
||||
if st["state"] == "failed":
|
||||
raise HTTPException(
|
||||
status_code=subtitles.UNAVAILABLE_STATUS.get(st["code"], 422),
|
||||
detail={"code": "subtitle", "reason": st["code"]},
|
||||
)
|
||||
hit = subtitles.cache_read(subtitles.cache_key(rating_key, sub_ord))
|
||||
if hit is None:
|
||||
return Response(
|
||||
status_code=202, media_type="application/json", content='{"state":"preparing"}'
|
||||
)
|
||||
return Response(subtitles.shift_vtt(hit, offset), media_type="text/vtt")
|
||||
|
||||
|
||||
# Resume/watched thresholds. _PROGRESS_MIN_S matches the feed's PROGRESS_MIN_SECONDS (5), but
|
||||
|
||||
@@ -0,0 +1,263 @@
|
||||
"""Subtitle extraction must not happen inside the request, and must read as little as possible.
|
||||
|
||||
Bug hunt 2026-09, item 8 — "switching the subtitle track shows nothing; after a few stop/starts it
|
||||
suddenly works". Measured on prod against a 17.06 GB MKV with two embedded SubRip tracks:
|
||||
|
||||
full pass, one track 154 s | both tracks in ONE run 111 s | a 630 s window at 1:00:00 8 s
|
||||
|
||||
The cost is not the WebVTT conversion, it is that ffmpeg streams every byte of the container between
|
||||
its seek point and its stop point. The old endpoint did that pass INSIDE the <track>'s request, once
|
||||
per track, with no timeout — so the browser sat on an empty track for minutes (and an API worker
|
||||
thread sat with it), and picking the second language cost the whole read again.
|
||||
|
||||
These tests pin the three things that fixes it: the request never waits for ffmpeg, the extraction
|
||||
publishes a window around the playhead before the whole track, and one ffmpeg run covers every
|
||||
embedded text track. Pure — no Postgres, no ffmpeg.
|
||||
"""
|
||||
|
||||
import subprocess
|
||||
import threading
|
||||
import time
|
||||
from pathlib import Path
|
||||
|
||||
import pytest
|
||||
from fastapi.testclient import TestClient
|
||||
|
||||
import app.state as app_state
|
||||
from app.main import app
|
||||
from app.plex import subtitles
|
||||
from app.routes.plex import playback
|
||||
|
||||
|
||||
@pytest.fixture(autouse=True)
|
||||
def _isolated_cache(tmp_path, monkeypatch):
|
||||
"""A throwaway cache root + empty registries: this module's state is process-global."""
|
||||
monkeypatch.setattr(subtitles, "CACHE_DIR", tmp_path)
|
||||
subtitles.reset_state()
|
||||
yield
|
||||
subtitles.reset_state()
|
||||
|
||||
|
||||
@pytest.fixture
|
||||
def client(monkeypatch) -> TestClient:
|
||||
# The subtitle endpoints authenticate off the signed session cookie directly (not a FastAPI
|
||||
# dependency), so there is no dependency_overrides hook to use.
|
||||
monkeypatch.setattr(playback, "resolved_user_id", lambda request: (1, None))
|
||||
monkeypatch.setattr(app_state, "_configured_cache", True) # pass the instance-setup gate, no DB
|
||||
return TestClient(app)
|
||||
|
||||
|
||||
class _ManualPool:
|
||||
"""Deterministic stand-in for the extraction thread pool: jobs run when the test says so."""
|
||||
|
||||
def __init__(self) -> None:
|
||||
self.jobs: list[tuple] = []
|
||||
|
||||
def submit(self, fn, *args) -> None:
|
||||
self.jobs.append((fn, args))
|
||||
|
||||
def run_next(self) -> None:
|
||||
fn, args = self.jobs.pop(0)
|
||||
fn(*args)
|
||||
|
||||
def run_all(self) -> int:
|
||||
jobs, self.jobs = self.jobs, []
|
||||
for fn, args in jobs:
|
||||
fn(*args)
|
||||
return len(jobs)
|
||||
|
||||
|
||||
def _cue(start: str, end: str, text: str) -> str:
|
||||
return f"{start} --> {end}\n{text}"
|
||||
|
||||
|
||||
def _vtt(*cues: str) -> str:
|
||||
return "WEBVTT\n\n" + "\n\n".join(cues) + "\n"
|
||||
|
||||
|
||||
# --- the request must never wait for the extraction ---------------------------------------------
|
||||
|
||||
|
||||
def test_a_cold_track_answers_at_once_instead_of_waiting_for_ffmpeg(client, monkeypatch):
|
||||
"""THE regression. A cold track used to block the request for the length of a full file read;
|
||||
now it answers 202 and the extraction runs behind it. Timed, because "does it block?" is the
|
||||
whole question — the fake extraction holds a worker for 5 s, which the request must not feel."""
|
||||
started = threading.Event()
|
||||
release = threading.Event()
|
||||
|
||||
def _slow(rating_key, sub_ord, window_start):
|
||||
started.set()
|
||||
release.wait(timeout=5)
|
||||
|
||||
monkeypatch.setattr(subtitles, "_extract_and_publish", _slow)
|
||||
try:
|
||||
t0 = time.monotonic()
|
||||
resp = client.get("/api/plex/subtitle/98614/0")
|
||||
elapsed = time.monotonic() - t0
|
||||
assert resp.status_code == 202, resp.text
|
||||
assert elapsed < 2.0, f"the request waited {elapsed:.1f}s on the extraction"
|
||||
assert started.wait(timeout=5), "the extraction never started in the background"
|
||||
# …and the status endpoint answers just as fast while that extraction is still running.
|
||||
t0 = time.monotonic()
|
||||
st = client.get("/api/plex/subtitle/98614/0/status")
|
||||
assert st.status_code == 200 and st.json()["state"] == "preparing"
|
||||
assert time.monotonic() - t0 < 2.0
|
||||
finally:
|
||||
release.set()
|
||||
|
||||
|
||||
def test_a_burst_of_polls_starts_one_window_and_one_full_pass(monkeypatch):
|
||||
"""The player polls once a second while it waits. Each poll must JOIN the running jobs, not
|
||||
start another ffmpeg over the same 17 GB."""
|
||||
pool = _ManualPool()
|
||||
monkeypatch.setattr(subtitles, "_POOL", pool)
|
||||
for _ in range(5):
|
||||
subtitles.ensure("98614", 0, at=600.0)
|
||||
assert len(pool.jobs) == 2 # one window (at 600 s) + the one full pass
|
||||
# submit(_run, ident, rating_key, sub_ord, window_start) — the last arg is what distinguishes them
|
||||
assert [a[3] for _, a in pool.jobs] == [570.0, None] # the window first, then the full pass
|
||||
|
||||
|
||||
# --- window first, whole track after ------------------------------------------------------------
|
||||
|
||||
|
||||
def test_status_walks_preparing_to_partial_to_ready(client, monkeypatch):
|
||||
"""A window around the playhead makes the track showable long before it is complete, and the
|
||||
generation changes when it grows so the browser refetches instead of keeping the short VTT."""
|
||||
pool = _ManualPool()
|
||||
monkeypatch.setattr(subtitles, "_POOL", pool)
|
||||
key = subtitles.cache_key("98614", 0)
|
||||
|
||||
def _publish(rating_key, sub_ord, window_start):
|
||||
if window_start is not None:
|
||||
subtitles.publish(
|
||||
key, _vtt(_cue("59:54.187", "59:58.650", "window")), (3570.0, 3900.0), False
|
||||
)
|
||||
else:
|
||||
subtitles.publish(key, _vtt(_cue("01:12.000", "01:15.000", "whole")), (0.0, 1e9), True)
|
||||
|
||||
monkeypatch.setattr(subtitles, "_extract_and_publish", _publish)
|
||||
|
||||
first = client.get("/api/plex/subtitle/98614/0/status?at=3600").json()
|
||||
assert first["state"] == "preparing" and first["gen"] == 0
|
||||
|
||||
pool.run_next() # the window job, submitted first — the full pass stays queued behind it
|
||||
windowed = client.get("/api/plex/subtitle/98614/0/status?at=3600").json()
|
||||
assert windowed["state"] == "partial", "a window around the playhead is showable"
|
||||
assert windowed["gen"] > 0
|
||||
# …and the <track> request now gets real WebVTT rather than another 202.
|
||||
served = client.get("/api/plex/subtitle/98614/0?at=3600")
|
||||
assert served.status_code == 200 and "window" in served.text
|
||||
|
||||
pool.run_next() # the full pass, scheduled by that same first poll
|
||||
done = client.get("/api/plex/subtitle/98614/0/status?at=3600").json()
|
||||
assert done["state"] == "ready"
|
||||
assert done["gen"] != windowed["gen"], "a widened track must not reuse the window's generation"
|
||||
assert "whole" in client.get("/api/plex/subtitle/98614/0").text
|
||||
|
||||
|
||||
def test_a_position_outside_the_extracted_window_is_not_called_showable(client, monkeypatch):
|
||||
"""Honest states: cues exist, but none for where the viewer just seeked to. Saying "ready" there
|
||||
would put an empty track on screen with no explanation — the original complaint."""
|
||||
pool = _ManualPool()
|
||||
monkeypatch.setattr(subtitles, "_POOL", pool)
|
||||
subtitles.publish(
|
||||
subtitles.cache_key("98614", 0),
|
||||
_vtt(_cue("00:10.000", "00:12.000", "x")),
|
||||
(0.0, 330.0),
|
||||
False,
|
||||
)
|
||||
assert client.get("/api/plex/subtitle/98614/0/status?at=100").json()["state"] == "partial"
|
||||
assert client.get("/api/plex/subtitle/98614/0/status?at=5000").json()["state"] == "preparing"
|
||||
|
||||
|
||||
def test_an_unshowable_track_says_why_and_maps_to_a_status(client, monkeypatch):
|
||||
pool = _ManualPool()
|
||||
monkeypatch.setattr(subtitles, "_POOL", pool)
|
||||
|
||||
def _bitmap(rating_key, sub_ord, window_start):
|
||||
raise subtitles.SubtitleUnavailable("bitmap")
|
||||
|
||||
monkeypatch.setattr(subtitles, "_extract_and_publish", _bitmap)
|
||||
client.get("/api/plex/subtitle/98614/0/status")
|
||||
pool.run_all()
|
||||
st = client.get("/api/plex/subtitle/98614/0/status").json()
|
||||
assert st["state"] == "failed" and st["code"] == "bitmap"
|
||||
resp = client.get("/api/plex/subtitle/98614/0")
|
||||
assert resp.status_code == 415 # a structured detail, so the UI can translate it
|
||||
assert resp.json()["detail"] == {"code": "subtitle", "reason": "bitmap"}
|
||||
|
||||
|
||||
# --- the ffmpeg pass itself ---------------------------------------------------------------------
|
||||
|
||||
|
||||
def _capture_ffmpeg(monkeypatch) -> list[list[str]]:
|
||||
"""Record the argv of each ffmpeg run and satisfy it by writing the outputs it asked for."""
|
||||
runs: list[list[str]] = []
|
||||
|
||||
def _fake_run(cmd, **kwargs):
|
||||
runs.append(cmd)
|
||||
for i, arg in enumerate(cmd):
|
||||
if arg == "-y":
|
||||
Path(cmd[i + 1]).write_text(_vtt(_cue("00:01.000", "00:02.000", "hi")), "utf-8")
|
||||
return subprocess.CompletedProcess(cmd, 0, b"", b"")
|
||||
|
||||
monkeypatch.setattr(subtitles.subprocess, "run", _fake_run)
|
||||
return runs
|
||||
|
||||
|
||||
def test_one_ffmpeg_run_extracts_every_embedded_text_track(monkeypatch):
|
||||
"""The read is the cost and it is SHARED. Extracting one track at a time is what made picking
|
||||
Hungarian cost a full pass and then switching to English cost another one."""
|
||||
runs = _capture_ffmpeg(monkeypatch)
|
||||
out = subtitles._ffmpeg_extract("/plex-media/f.mkv", [0, 1], None, None)
|
||||
assert len(runs) == 1, "each extra ffmpeg run is another full read of the file"
|
||||
assert set(out) == {0, 1}
|
||||
assert runs[0].count("-map") == 2
|
||||
|
||||
|
||||
def test_a_windowed_pass_bounds_the_read_and_never_uses_copyts(monkeypatch):
|
||||
"""`-copyts` is the trap: with it ffmpeg IGNORES -t and reads the whole container anyway
|
||||
(measured — a [0, 600 s] window still took the full 145 s). So the window is extracted on a
|
||||
zero-based clock and shifted back to absolute time by the caller."""
|
||||
runs = _capture_ffmpeg(monkeypatch)
|
||||
subtitles._ffmpeg_extract("/plex-media/f.mkv", [0], 3570.0, 330.0)
|
||||
cmd = runs[0]
|
||||
assert "-copyts" not in cmd
|
||||
assert cmd[cmd.index("-ss") + 1].startswith(
|
||||
"3570"
|
||||
) # input seek — before -i, so it is a real seek
|
||||
assert cmd.index("-ss") < cmd.index("-i")
|
||||
assert cmd[cmd.index("-t") + 1].startswith("330")
|
||||
|
||||
|
||||
def test_the_full_pass_is_not_bounded(monkeypatch):
|
||||
runs = _capture_ffmpeg(monkeypatch)
|
||||
subtitles._ffmpeg_extract("/plex-media/f.mkv", [0], None, None)
|
||||
assert "-t" not in runs[0] and "-ss" not in runs[0]
|
||||
|
||||
|
||||
# --- the pure pieces the above rests on ---------------------------------------------------------
|
||||
|
||||
|
||||
def test_merge_vtt_unions_windows_in_time_order():
|
||||
late = _vtt(_cue("59:54.187", "59:58.650", "late"))
|
||||
early = _vtt(_cue("01:12.000", "01:15.000", "early"), _cue("59:54.187", "59:58.650", "late"))
|
||||
merged = subtitles.merge_vtt(late, early)
|
||||
assert merged.startswith("WEBVTT\n\n")
|
||||
assert merged.count("-->") == 2, "the shared region must not be duplicated"
|
||||
assert merged.index("early") < merged.index("late")
|
||||
|
||||
|
||||
def test_covered_ranges_coalesce_and_answer_membership():
|
||||
ranges = subtitles.merge_ranges([[300.0, 600.0], [0.0, 330.0], [900.0, 1200.0]])
|
||||
assert ranges == [[0.0, 600.0], [900.0, 1200.0]]
|
||||
assert subtitles.covers(ranges, 450.0)
|
||||
assert not subtitles.covers(ranges, 700.0)
|
||||
|
||||
|
||||
def test_a_cached_vtt_from_an_older_build_counts_as_complete(tmp_path):
|
||||
"""Before this change the cache only ever held whole tracks, and none of them has a sidecar.
|
||||
Reading one as "covers nothing" would re-extract every already-cached track after the upgrade."""
|
||||
(tmp_path / "sub_98614_0.vtt").write_text(_vtt(_cue("00:01.000", "00:02.000", "x")), "utf-8")
|
||||
assert subtitles.read_meta("sub_98614_0") == ([[0.0, 1_000_000_000.0]], True)
|
||||
Reference in New Issue
Block a user