[mythtv] Transcoding AC3/5ch and video sync

[Jesse Crews]

Quoting Mark Spieth <mark at dclabs.com.au>:


> I suspect you arent using my multichannel audio patch. The above discussion
> is then irrelevant.

nope

> the a52dec does the downconverting to 2ch always in a standard .20 myth
> build.
> the timestamps are calculated against blocks. you will see slight jitter

In the case of 5.1 AC3, it seems that the timestamps are 300ms behind  
what they usually are. I'll be running some mythtranscode -a all for  
various 2 and 6 channel content on the same channel, and compare the  
results.

> between audio and video timestamps but they will keep in sync unless
> something is drastically wrong.

They're doing this just fine, just 300ms off for some reason. There  
isn't any drift at all.

> the sync adjust is in nvp and while you could do something automatically, Id
> suggest that there is probably something wrong with the stream. lavc a52dec
> does a good job at downconverting all combinations.

In the end, I might end up doing either:
-Detect AC3 has 6 channels, and set the sync adjust to -300ms
-Detect AC3 has 6 channels, and adjust the timestamp math accordingly.

I think any way I look at this, the only solution will be to check the  
number of channels in the audio, and act accordingly, since the  
timestamping already works fine for 2 channels. The only two flavors I  
have is stereo and 5.1 channel surround.

> perhaps there needs to be some defaults for various channel/stream types for
> setting some things automatically.
> or perhaps a transcode jobsched which you can shift audio by a specified
> amount.
> cheers
> mark
>
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