YouTube now packs AV1 inside .mp4, so the old `bv*[ext=mp4]` format selector
grabbed AV1 for the downloaded ORIGINAL. Premiere rejects AV1 on hi-res import
("unsupported file type"). The h264 proxy was fine, but the original wasn't.
Prefer avc1 (H.264) so the original is Premiere-native, falling back to the
previous any-mp4 behaviour only when no H.264 rendition exists. avc1 tops out
at 1080p on YouTube (above that is AV1/VP9 only), which is the universally
importable ceiling anyway.
Verified on a real URL: old selector -> av01 1080p; new selector -> avc1 1080p
(same resolution, now Premiere-native).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>