Hi Jay,
> I need to convert some PAL high-quality divx AVIs to SCVD mpeg. I have
> a tool chain that works fine for NTSC sources. I use transcode to
> convert the divx source to a mjpeg-tools LAV file as follows:
>
> $ transcode -i foo.avi -y ffmpeg -F mjpeg -V -N 0x1 -f 25,3 -o
> foo.lav.avi
>
> then use mjpeg-tools lav2mpeg script to convert to mpeg:
>
> $ lav2mpeg -m svcd -o foo-svcd.mpg foo.lav.avi
>
> I mix the tools this way because I've found it gives the best trade off
> for speed/quality/consistency than any of the other combinations I've
> tried.
You're definately taking a quality hit going DivX->MJPEG->MPEG rather than
going direct DivX->MPEG direct. There's probably folk on the list here who
can give you good recipes for the direct conversion. I know for sure
transcode can directly generate the "YUV4MPEG" files that my MPEG encoder
expects.
> The same system works fine for PAL, except it gives me a PAL formatted
> (480x576 25fps) mpg file. My thought is that since the mjpeg LAV file
> is frame oriented, it should be relatively straightforward to encode it
> to NTSC standards. But I may be way off base.
Semi-straightforward. The problem is that PAL runs at 50 fields/25 frames
sec . For NTSC you want 60/30 (well actually 1000/1001 times that many).
Someplace some frame-rate conversion is necessary. If the original material
was a Movie (24 frames/sec) its not too bad. Movies are almost always simply
run 25/24 times too fast for PAL so all you have to do is slow down the audio
track and tell mpeg2enc to set the 3:2 pulldown flags needed to playback
movie material under NTSC. If the original material was video or worse
still NTSC video converted to PAL video the conversion process is going to be
a nightmare!
> PS - The lav2mpeg step above is pretty darn slow - it takes upwards of 4
> hours to convert about 25 minutes worth of video on my Athlon 1100. If
> that is about par for the course, fine. I just want to make sure I'm
> not doing something stupid to make the process slower than it has to be.
Hmmm.... that is rather slow. lav2mpeg is probably setting the motion
estimator in mpeg2enc to the very very CPU expensive "squeeze out the last
drop" settings. This is pretty much always not necessary. I personally run
the estimator either in a fast mode or default. The gains from turning it
right up are pretty trivial most of the time.
Andrew
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