Opened 13 years ago

Closed 12 years ago

#4819 closed defect (duplicate)

Faint audio from 5.1 upmix on MPEG-4 files

Reported by: Yeechang Lee <ylee@…> Owned by: danielk
Priority: minor Milestone: unknown
Component: mythtv Version: head
Severity: medium Keywords: mpeg-4 xvid divx upmix multichannel audio stereo active linear simple passive 5.1
Cc: Ticket locked: no


I am running r16254, and have noticed this issue since the multichannel audio support in #1104 was committed to trunk. Relevant ./configure flags are --enable-libx264, --enable-libmp3lame, --enable-libfaad, --enable-libfaac, --enable-libfftw3.

My frontend outputs audio via S/PDIF. I have AC3 and DTS passthrough enabled. My Myth recordings are all originally in MPEG-2 (via OTA or FireWire?); many have AC3 tracks. Some recordings have since been converted by mythtranscode into MPEG-4, which also downmixed any AC3 tracks into stereo. I also play via MythVideo? various AVI files in both Xvid and Divx formats with either AC3 or MP3 audio.

If I set Max Audio Channels to 5.1 and Upmix to either Active Linear or Active Simple, here is what I get audiowise with various video/audio combinations, with no timestretch used:

  • MPEG-2/AC3: No problem.
  • MPEG-2/non-AC3: No problem.
  • MPEG-4/non-AC3: Audio is so faint it's almost inaudible.
  • Xvid/MP3: Audio is so faint it's almost inaudible.
  • Divx/AC3: No problem.

The audio problems go away if I either set Max Audio Channels to Stereo, or keep Max Audio Channels at 5.1 but set Upmix to Passive.

Brad Dermanouelian reports the same issue with his analog card-captured MPEG-4 MythTV recordings.

Change History (6)

comment:1 Changed 13 years ago by Matt S <skd5aner@…>

I'm also getting this with some MPEG2 videos with MP3 audio (not recordings). Barely Audible sound, also sounds washed out.

comment:2 Changed 13 years ago by danielk

Owner: changed from Isaac Richards to danielk
Status: newassigned

Does this still happen when ./configure is run with no options?

comment:3 Changed 13 years ago by Matt S <skd5aner@…>

Daniel - have not tested with just ./configure. Here were my configure options:

./configure --enable-proc-opt --disable-xvmcw --enable-xvmc-opengl --enable-o

pengl-video --enable-opengl-vsync --enable-libfftw3 --xvmc-lib=XvMCNVIDIA

Also - I need to clarify my last comment above - It was MPEG4 video with MP2 audio. I can submit a sample off-list if needed.

comment:4 Changed 13 years ago by Matt S <skd5aner@…>

I also explained my issues, which match up with those described in the ticket, in this thread:

comment:5 Changed 12 years ago by ylee@…

I am pleased to report that #5900 does, as its creator noted, appear to fix this issue, regardless of whether the upmixer is turned on or not.

comment:6 Changed 12 years ago by Dibblah

Resolution: duplicate
Status: assignedclosed

Will be fixed when #5900 is committed

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