[mythtv-users] transcoded nuv/mpeg4: really mpeg4?
ijr at case.edu
Thu Aug 18 17:43:42 UTC 2005
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.
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