[mythtv-users] transcoded nuv/mpeg4: really mpeg4?

[Isaac Richards]

On Thursday 18 August 2005 01:12 pm, Brian J. Murrell wrote:
> > It contains _no_ syncing
> > information.  A straight repack will lose av sync extremely rapidly. 
> > ogg's pretty much the same way.
>
> But they stay in sync somehow.

Right - if you're reencoding from another source, you can make something that 
stays in sync.  

AVI assumes that audio + video data is at a constant framerate.  It doesn't 
have any concept of timestamps.  For regular TV, that's just not true.  For 
stuff recorded by a soundcard, that's even less true - the soundcard's clock 
varies over time.  You ask for 48000 samples per second, and what you get 
won't be that exactly, and will change over time as well.

In a nuv file, each frame of video, and each packet of audio has a timestamp 
associated with it.  There are also additional constructs for dealing with 
skipping individual frames (for exact frame-level cuts during a transcode 
without reencoding), and other various things that make it rather ideal for 
dealing with stuff recorded from a tuner card.

Isaac