[mythtv] Looking for details on myth-rtjpeg codec

Dave Caplinger mythtv-dev@snowman.net
Tue Jan 7 04:22:24 EST 2003

On Mon, 2003-01-06 at 00:12, Matt Zimmerman wrote:
> Uncompressed audio should work OK; did you try playing only the audio with
> mplayer?

In MPlayer-0.92rc2/libmpdemux/demuc_nuv.c, this is the line that crashed

    sh_audio->i_bps = nearestBitrate(ext.audio_channels
      * ext.audio_bits_per_sample * ext.audio_sample_rate /
      ext.audio_compression_ratio / 1000) * 1000;

so, I put an "if (sh_audio->format == 0x55 )" around it under the
assumption that this code must work for you on your MP3 audio streams
but that it didn't make a whole lot of sense to worry about for raw PCM

> You already have my mplayer patch; that's probably the best possible example
> of the changes that are required in order for a nuppelvideo-aware program to
> understand MythTV streams.

I may not have been completely clear; I'm assuming that Myth RT-JPEG
streams are not the same thing as NuppelVideo RT-JPEG streams.  It this
wrong?  Note that this is a different issue than whether the Myth .nuv
container file format is different than NuppelVideo's, which is of
course true.

Maybe I'm completely confused but I was thinking that there are three
main things to worry about: stream container file format, video stream
format, and audio stream format.  Am I wrong in thinking that (original)
NuppelVideo is a container file format that contains an RT-JPEG video
stream and a uncompressed PCM audio stream, while the Myth container
adds the ability to use MPEG4 video streams and MP3 audio streams, *AND*
changes the RT-JPEG stream format (and also the container file format is
changed to accomodate the new a/v stream formats)?

The last part (about the RT-JPEG being different in Myth than in Nuppel)
is substantiated by Isaac's post to the list on 23-Aug-2002, where he
said (in relation to using existing tools to convert Myth files to VCD):

> Well, they'll have to be modified -- the original Nuppelvideo didn't
> compress the audio, used a different version of rtjpeg. Oh, and didn't
> use mpeg4 as an option, either =) But, yes, the framework's there, and
> those should be relatively minor changes to the existing tools to get
> them to grok the changes.

So... what is the difference between the two RT-JPEG formats and why was
this change in format necessary?  This is mostly for my own curiosity
and understanding; I'm certainly not trying to be argumentative.

Dave Caplinger <dent@cox.net>

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