[mythtv-users] nuvexport audio sync

[Jean-Yves Avenard]

On 2 May 2011 14:42, Gavin Hurlbut <gjhurlbu at gmail.com> wrote:

> Ahh.  Gotcha.  So with what you have now, fifo mode *can* do straight
> passthrough with another commandline option?  That would be kinda cool for
> future functionality in nuvexport. :)  Anyways, with your latest changes, I
> guess I'll need to re-tweak to get it working again, which is the price we
> pay for progress.

The option is --passthrough in the mythtranscode command line. That
option should be added to the recording profile editor, the problem is
that unless you're using fifo mode ; the destination container (mp3 or
nuv) doesn't know how to deal with the resulting data. The NUV
container can't even have anything else but a mp3 or stereo 16bits PCM
audio stream

Previously, avfd would always decode all the channels of the audio
stream and pass it to mythtranscode ; when most of the time the new
destination container would have been expecting stereo.
In FIFO it didn't matter, because that's what fifo does: just output
all that was decoded.

The *fix* I'm referring to, only force avfd to only decode stereo and
pass that to mythtranscode... Adding the ability to handle more than
stereo isn't complicated as such, but mythtranscode never had any of
the internal logic to handle different channel numbers. There's not
even a member variable specifying how many channels we are expecting
:(

The reason avfd used to decode all channels, was to prevent the issue
with AC3 audio being at different audio level. The main audio class
knows how to downmix, but the dummy audio class in mythtranscode has
no clue of that.
If there was an easy way to tell how many channels we are expecting in
the end, I could make avfd decode all channels once again and add a
downmixer in mythtranscode as required.

But I'm not sure it's worth fixing mythtranscode if the aim is getting
a mkv transcoder instead... but the task for that one is daunting.
JY