mp4 downloads used yt-dlp's default best video+audio, which on YouTube is
VP9+Opus at 1080p. Chromium plays that, but iOS/Safari WebKit (which every
iOS browser is forced to use) decodes only H.264/H.265+AAC inside mp4 — so a
shared /watch link showed a broken player on iPhone/iPad while the download
still worked. Rank vcodec:h264 + acodec:aac above resolution for mp4 output
(unless a custom profile pins a vcodec), keeping VP9/AV1 as a graceful
fallback. Bump the format signature (v2) so an identical spec gets a fresh
cache identity instead of hitting a stale VP9 asset.
peter
ddfe1854e9