[mythtv] A/V Sync problem only on some PBS Hi-def shows

Michael T. Dean mtdean at thirdcontact.com
Thu Apr 17 02:18:17 UTC 2008

On 04/16/2008 12:12 AM, DaveD wrote:
> Steve Wilson wrote:
>> --- DaveD wrote:
>>> I've posted this problem a couple of times to the
>>> users list, so far no 
>>> solutions.  I have bad (unwatchable) A/V sync on
>>> some of our 720p HD PBS 
>>> shows.  Some shows (Desert Speaks) always work, some
>>> shows (e2) never 
>>> work. ...
>> I had that problem and it was only on the high-def PBS
>> channel as the sound would wobble really bad and that
>> was the only channel. I either turned on or off
>> Aggressive Sound Card buffering under Setup -> General
>> and the problem went away. I can't remember which way
>> since I built a new system.
> Thanks for the response.  I'm not sure I got the right setting, but I 
> tried turning TV Settings / Playback / Extra Audio Buffering off and it 
> broke ALL 720p playback, not just the problem shows.

The one Dave mentioned:

Aggressive Sound card Buffering
If enabled, MythTV will pretend to have a smaller sound card buffer than
is really present.  This may speed up seeking, but can also cause
playback problems.

should be off.  (Under General Settings, about page 2.)

However, for almost all not-Myth-encoded video (hardware encoders and
DVB/ATSC capture cards):

Extra audio buffering
Enable this setting if MythTV is playing "crackly" audio and you are
using hardware encoding. This setting will have no effect on MPEG-4 or
RTJPEG video. MythTV will keep extra audio data in its internal buffers
to workaround this bug.

should be on.  If you did your test of Extra audio buffering with
Aggressive Sound card Buffering on, the results are meaningless.


More information about the mythtv-dev mailing list