Tunneled playback on an AFTMM judders continuously through 23.976p direct play.
The #1802 reporter isolated it: turning off Tunneled Playback with every other
setting unchanged makes it smooth, and their log shows tunneling active for the
whole session with E-AC3 bitstreamed and the decoded-PCM guard never firing.
Audio Passthrough looked like the trigger only because it is the one user-facing
switch that decides it. Passthrough off, or Downmix to Stereo on, both force the
Dolby track to decode to PCM, which trips the #1458 guard and takes tunneling
down with it. Passthrough on with downmix off is the only combination that keeps
a bitstreamed track, so it is the only one that stays tunneled.
Withdraw tunneling on that model for content at or below 30fps. The cut-off
keeps 4K50/60 tunneled, which is the workload Amazon documents the feature for.
The mechanism stays unconfirmed: tunneling fires no VideoFrameMetadataListener
and stops media3 counting frames in the codec, so nothing app-side can measure
the cadence. Only the trigger is established, and the quirk is scoped to it.
That needs a frame rate the app did not have. Neither MatroskaExtractor nor
Mp4Extractor populates Format.frameRate, and a tunneled session renders no
frames back for the native detector, so the server's rate now rides on the open
call. It is sent only for direct play, matching _primeDisplayCriteria: a
transcode's metadata describes the source, not what the server is about to send.
Also move Audio Passthrough out of the in-player settings sheet. It configures
the audio output route rather than the current playback, and applying it
mid-stream bounces the audio renderer and re-decides tunneling. Settings > Video
Playback already owns it, next to Tunneled Playback, which is applied the same
way. That description now mentions stutter, not only black HDR video, so the
workaround is findable on hardware this quirk does not cover.
The mpv backend failing to start the same 4K file is a separate defect and is
not addressed here; its uploaded log is no longer retrievable.
edde746
f93952ba6f