[mythtv-users] ac3 passthrough results in accelerated video

scram69 scram69 at gmail.com
Sat May 31 04:38:22 UTC 2008


On Thu, May 29, 2008 at 8:38 PM, scram69 <scram69 at gmail.com> wrote:
> On Thu, May 29, 2008 at 8:18 PM, John P Poet <jppoet at gmail.com> wrote:
>> On Thu, May 29, 2008 at 8:24 PM, Craig Treleaven <ctreleaven at cogeco.ca> wrote:
>
>>> Me too.  I'm running .21-fixes (from a couple of months ago) on a Core2Duo mini.  The problem recordings will play in accelerated mode one, two or three times in a row and then play fine.  Lots of recordings play fine.  I think I only see this problem with ABC, NBC and CBS; not with the Canadian networks.  BTW, all are recorded OTA via an HDHomerun.
>>>
>>> Also, the frontend hangs on exiting playback, sometimes.  I keep meaning to set up logging but haven't done it yet.
>>>
>>> Neither of these problems happened to any extent under .20-fixes.  As you might imagine, it is having a detrimental effect on the SAF (spousal approval factor).  Thanks to scram69 for pointing out the issue and the correlation with digital audio--I had no idea that was related!
>>>
>>> On the Mac, what is a good tool identify the types of audio and video data in a file?  VLC doesn't give any details.
>>
>>
>> One *big* change between 0.20 and 0.21 is that once you turn on
>> timestetch while watching a show, it never turns back off -- even if
>> you go back to 1.0x speed.  As part of this, it *decodes* DD5.1,
>> adjusts it's speed (if necessary), then re-encodes the audio back into
>> DD5.1 (preserving the original channel allocation) and sends it out
>> your S/PDIF.  This is actually all pretty cool, but it has introduced
>> some new problems.
>>
>> If you are getting loud static popping, I wonder if it is not
>> correctly re-encoding the DD5.1?  I have not tried this in a *long*
>> time, but you used to be able to change to a different ac3 library by
>> compiling with:
>>
>> configure --enable-liba52bin --disable-decoder=ac3 --enable-decoder=liba52
>>
>> Mark Spieth would have to comment on whether that still works.  Of
>> course your problem might also be that no ac3/a52 library is being
>> linked in at all...
>>
>>
>> If timestretch is "on", then it can occasionally get confused by the
>> audiostream and miss-detect "6 channels" as "2 channel", which results
>> in a chipmunk sound.  For example see:
>>
>> http://svn.mythtv.org/trac/ticket/5126
>>
>>
>> You can post a (possibly) useful log if you run mythfrontend with audio logging:
>>
>> mythfrontend -v audio,libav,playback -l somelogfile
>>
>>
>> Hope some of this info is useful.
>>
>> John
>
> John - quite useful and timely.  I was just searching through the
> archives attempting to dredge up the flags necessary to target audio
> logging.
>
> Craig - my recordings are all cable, but also via HDHomerun.  The
> troubleshooting was basic Murphy - I only bothered with the hassle of
> upgrading in order to get AC-3 on my main home theater frontend -
> therefore, when the problems started creeping up, AC-3 was the most
> likely culprit :(
>
> I'll get to work on the log-
>
> Steve
>

So I've been running 24 hours with AC-3 passthrough enabled and the
verbose audio logging turned on, and, of course, Mythfrontend is on
it's best behavior.  No instances of accelerated playback.

Just in case I've run up against some quantum limit, collapsing the
wavepackets in my attempt to quantify the randomness, is there any way
to configure the app on OS X to always run with this type of verbose
logging?


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