Four bugs, one cause. "What can this device decode" was answered in five
places, four of which assumed the webview was decoding:
- the device profile's direct-play codecs (cfg per platform, inline)
- the transcoding targets (hardcoded "h264,hevc")
- the direct-play audio narrowing (webview list, all platforms)
- the client-side audio override (webview list, all platforms)
- get_video_stream_url's VideoCodec (hardcoded "h264")
On Android the decoder is ExoPlayer, so four of those were simply wrong there,
and the costs were invisible without a device:
- dts is in the tablet's own codec list, gets stripped from the profile, and
is then forced to transcode by a rule about a renderer that is not playing
it.
- An hevc source whose *audio* is eac3 had its **picture fully re-encoded**.
The server's own transcoding URL got this right — VideoCodec=h264,hevc,
TranscodeReasons=AudioCodecNotSupported, video copied — but the moment a
quality change or track switch re-opened the stream through our builder,
the hardcoded h264 turned a cheap audio remux into a full transcode. That
is a quality change silently making playback more expensive, on the exact
path a viewer uses when playback is already struggling.
`renderer_codecs()` and `renderer_can_decode_audio()` are now the single
source, and all five sites read them. On the webview path every value resolves
exactly as before, so desktop behaviour is unchanged by construction; on
Android the profile becomes the device's own.
The list is also what lets the server *copy* rather than re-encode: naming
every codec the renderer can decode is what turns a transcode into a
passthrough when the source is already playable. That is the whole of "use the
best format available".
Also corrects this branch's headline number where it is asserted — the
architecture doc, the desktop-native-video spec and the spike. The measured 85%
Android direct-play rate used a profile containing ac3/eac3; the device it was
later verified on reports neither, so eac3 content correctly transcodes there.
It is a ceiling for an ExoPlayer-appropriate profile, not what the app achieves,
and realising any of it depends on this change. Left in place with the caveat
rather than deleted, because the measurement is real — it just measures
something narrower than it was quoted as measuring.
Unverified: this changes what Android negotiates and has not been exercised on
the tablet yet. Desktop is unchanged by construction but also unre-tested.
dtourolle
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