[MEncoder-users] Audio Sync issues

[Rolf Ernst]

-----Original Message-----
From: mencoder-users-bounces at mplayerhq.hu
[mailto:mencoder-users-bounces at mplayerhq.hu] On Behalf Of Jeff Cranmer
Sent: Friday, September 16, 2011 9:33 PM
To: MEncoder usage discussions
Subject: Re: [MEncoder-users] Audio Sync issues

On Fri, 2011-09-16 at 15:53 -0500, Rolf Ernst wrote:
> On Fri, Sep 16, 2011 at 1:45 PM, Jeff Cranmer
<jeff at lotussevencars.com>wrote:
> 
> > -mc 0 didn't seem to help.
> > Perhaps I'm misunderstanding this, but wouldn't we want to set the 
> > number to something else other than 0, to allow the program to A-V 
> > sync sucessfully?
> >
> > On Fri, 2011-09-16 at 09:35 -0400, Jeff Cranmer wrote:
> > > > About the -noskip option:  maximum A-V sync correction per frame 
> > > > (in
> > > > seconds) -mc 0 should always be combined with -noskip for 
> > > > mencoder, otherwise it will almost certainly cause A-V desync.  
> > > > I don't know if that will help.  All you can do is try it.
> > > >
> > > > Bill
> >
> > Jeff,
> 
> what he says is correct - normally you want to set it to 0 which means 
> 'don't deviate at all from the a/v sync'. That being said - I have 
> never used it with the PVR encodes, not sure whether it would be of 
> benefit or detriment - I just don't have any sync issues. I will give 
> it a try using -oac pcm and see whether this might play into it.
> 
> Part of the problem could be that I don't think pcm has timecodes 
> built into it, just x number of samples/sec whereas if you copy the 
> AC3 stream that has timecodes. This becomes important as there are 
> occasional 'glitches' in the recordings that the PVR makes. It's 
> really of no big importance as the playback can always recover because 
> of the timecodes for both the audio and video stream. (Look months 
> back in this list and you will see how I brought it up before). Since 
> the pcm does not carry timecode information the occasional glitch 
> might throw it off, just a hypothesis. Just for grins I would suggest 
> to do an -oac copy and see whether this solves the problem. At least you
will know where to look then.

So far, I've had no luck with -oac copy, as I get an error when I try it.
The audio stream appears to be AAC rather than AC3.  Does this change
anything?  

Ah, there's something to look into. I assume you are using TM2 to record?
One of the settings is whether you want to record 2 channel audio (which
your source seems to be) as AAC or AC3. Switch it to AC3 and see how that
works for you.

Yes, I never quite understood why you couldn't do copy with AAC. If you use
YAMF (ahem, a little thing I wrote) it'll let you copy AAC but you may not
want to delve into yet another tool....

/re