[mythtv] NuppelVideo(Recorder/Player)

Isaac Richards ijr at po.cwru.edu
Mon May 19 00:29:06 EDT 2003

On Sunday 18 May 2003 05:11 pm, Craig Longman wrote:
> i understand that it wasn't transcoded, i'm just suspicious that i get
> the same sort of problem while transcoding, that's all.  it _looks_ to
> me like this screenshot was examining a .wav file, which is raw pcm
> data, right?  so if the problem is in the actual decoding of the layer2
> data, wouldn't it still show up in this case also?  

It's not a problem in the decoding, as the whine goes away when a different 
initialization sequence is used (pre msp3400 module in ivtv CVS).

> anyway, perhaps i 
> spoke too soon comparing my whine to your whine, i was thinking out
> loud.  i definitely have the problem, and the problem is definitely in
> the conversion, and seeing as other people have been using mythtv to
> write out mpeg4 files with 32K mp3 audio, it seems like the problem has
> to be in the layer2 decoding area.  i'm still trying to figure out where
> in mythtv the layer2 stuff is decoded, so i'll keep poking away.

It'd be in libavcodec.  But, lowing the whine that's present in the recordings 
(and I guarantee you that it is) by treating the 48kHz data as 32kHz as the 
transcode stuff does will make it _much_ more audible.

> here's a question though.  i had thought the data coming out of the card
> was mjpeg, you indicate its mpeg2, but the source code i'm looking at
> seems to interpret it as mpeg1video.  the 'raw' data coming out of the
> pvr250 is actually what format?  or where can i look for a description
> of the various m(j)pegs?

mpeg1/2 are quite similar -- mpeg2 is (very roughly) a set of extensions on 
top of mpeg1.  mjpeg's a much simpler format, and no, the pvr-250 doesn't 
make mjpeg video.  There's a bunch of faqs linked to at www.mpeg.org, if 
you're really interested..


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