[mythtv] [mythtv-commits] Ticket #5552: AC3 passthrough causes accelerated playback on OSX 0.21 frontend

Michael T. Dean mtdean at thirdcontact.com
Sat Jul 19 05:52:32 UTC 2008

On 07/18/2008 10:32 PM, Craig Treleaven wrote:
> At 12:37 AM -0400 7/18/08, Michael T. Dean wrote:
>> On 07/17/2008 12:45 AM, MythTV wrote:
>>> #5552: AC3 passthrough causes accelerated playback on OSX 0.21 frontend
>>> When AC3 passthrough is selected on the OSX frontend, occasionally the
>>> video an audio begin playing at an accelerated rate.  This usually happens
>>> when the show is not bookmarked - i.e. playback starts from the beginning
>>> of the file.  It never happens if AC3 passthrough is un-checked.
>>> I've attached a log file.  The accelerated playback session begins at the
>>> top of the file and ends at 21:29:24.  The normal playback session begins
>>> immediately afterward at 21:29:25.  The most obvious difference between
>>> the two is the appearance of a slew of " NVP: Video is x.xxxx frames
>>> behind audio (too slow), dropping frame to catch up." messages once
>>> playback begins in the first case.
>> Are you sure the broadcaster isn't switching to 32kHz AC-3 at that location and your sound card is continuing to read data at 48kHz?  Most all computer-based sound cards work only with 48kHz AC-3.
>> http://www.gossamer-threads.com/lists/mythtv/users/275748#275748
> I don't think this is the problem since the exact same portion of the recording will sometimes play fine and other times play in accelerated mode.

It would do exactly that if something disabled passthrough (or caused 
Myth to re-encode to 48kHz AC-3--which I think it can now do for 


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