Opened 12 years ago
Closed 12 years ago
Last modified 12 years ago
#11941 closed Bug Report - General (fixed)
No audio playback on DVDs with 16-bit stereo PCM audio tracks
| Reported by: | peper03 | Owned by: | JYA |
|---|---|---|---|
| Priority: | minor | Milestone: | 0.27.1 |
| Component: | MythTV - Audio Output | Version: | 0.27-fixes |
| Severity: | medium | Keywords: | |
| Cc: | salstrom@… | Ticket locked: | no |
Description
As reported here: http://www.gossamer-threads.com/lists/mythtv/users/557298 playback of DVDs with 16-bit stereo PCM audio tracks results in no audio and lots of 'audio decoder error' messages in the log.
ffmpeg sets the required codec to 'AV_CODEC_ID_PCM_DVD', which is only valid for 20 or 24 bits per sample. Normally this should be changed to AV_CODEC_ID_PCM_S16BE if the bit-depth is 16 bits, but for some reason this is no longer happening.
A small sample DVD image to reproduce the problem is available in stuartm's DVD repository under the name 'LongIntro_S16PCM.iso'
Change History (6)
comment:1 by , 12 years ago
comment:2 by , 12 years ago
our code shouldn't rely on any callback to detect a change in format.
the callback is only used when there's a change in a mpegts container.... it's a hack and we shouldn't rely on it in the future...
checking that the format hasn't changed from within avfd is the proper way to go; it's also there that change to resolution and format should be handled; outside any callback.
comment:3 by , 12 years ago
| Resolution: | → fixed |
|---|---|
| Status: | new → closed |
comment:5 by , 12 years ago
The fix worked and I now have audio on these types of situations. Thanks!
comment:6 by , 12 years ago
| Milestone: | unknown → 0.27.1 |
|---|
Appears to be the same problem as in #11519 (or very similar). In this case, there is only one audio track so AvFormatDecoder::ScanStreams doesn't get called again, and the decoder doesn't get re-initialised.
The problem appears to be that PCM encoded audio is assumed by ffmpeg to be 20 or 24 bits per sample, so is marked as 'AV_CODEC_ID_PCM_DVD'. Then the 'streams changed' callback is called and MythTV opens the PCM_DVD codec. When control returns to ffmpeg, it determines that the sample depth is only 16 bits, changes the codec to 'AV_CODEC_ID_PCM_S16BE' but doesn't call the callback. Because of this, MythTV isn't informed of the change and the 16-bit data is fed to a decoder expecting 20 or 24 bits per sample.