A device with no hardware HEVC decoder could still be handed an HEVC
transcode: the device profile advertised a fixed codec list that assumed
every device decodes everything. Prepending AV1 to reach the AV1 encoders
issue #2131 asks for would have made that worse - an Apple TV 4K and every
iPhone before the A17 Pro have no AV1 decoder at all.
Probe the platform instead. Android enumerates MediaCodecList for a
hardware decoder and iOS/tvOS ask VideoToolbox, both feeding one latched
VideoDecodeCapabilities that the device profile reads when it builds its
codec lists. Desktop deliberately answers nothing: a pre-Kaby-Lake Mac has
no hardware HEVC decoder and an M1 no AV1 one, yet both software-decode in
real time, so narrowing there would force transcodes for nothing. An
unanswered or failed probe advertises everything, so the list never
narrows on missing data.
The transcode target becomes av1,hevc,h264 filtered by the probe. Leading
with AV1 is safe because the server rotates codecs its admin has not
enabled ("Allow encoding in HEVC/AV1 format", both off by default) to the
back before picking one, so it costs nothing on a server that will not
emit AV1.
Audio now accepts everything the path can carry. The direct-play profile
drops its AudioCodec list entirely - an omitted list means "any codec" to
Jellyfin - so an audio stream can no longer be what blocks direct play.
The transcode target lists every codec Jellyfin can put in an fMP4
segment, so a video-only transcode copies DTS or TrueHD instead of
re-encoding it. Two limits bound that string: the server validates it
against ^[a-zA-Z0-9\-\._,|]{0,40}$ when it echoes the list into the
transcode URL, so alac does not fit and * is not a wildcard; and omitting
the key is not "accept everything" here the way it is for direct play,
because the server substitutes the source codec and then ships no audio at
all for a source fMP4 cannot carry.
close#2131
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