[MPlayer-users] TV/video capture - 2 pass
D Richard Felker III
dalias at aerifal.cx
Fri Dec 6 06:34:03 CET 2002
On Fri, Dec 06, 2002 at 11:38:29AM +0800, Mike Holland wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
>
> To get better quality video capture, it seems logical to do 2 passes.
> Compress to a reasonable size in realtime, and then do a second pass
> without realtime constraints.
>
> I tried the lavc/mpeg4 built-in 2-pass, but no luck. I'm assuming it
> requires the original input for the second pass, so no good for video
> capture?
>
> Whats the alternative? Is there a codec that gives less compression, but
> better quality and lower CPU demand? It would be good, but not essential,
> if the intermediate format was playable. Then I can choose to watch, or
> compress further for archiving.
Yes. vcodec=mjpeg:vqscale=2. It will use a lot of disk space, though.
However you can go back later and recompress with the normal two-pass
procedure and get the size down reasonably without much quality loss.
> ALSO: I have tried the lavc/mjpeg coder, but it doesnt produce the
> requested bitrate,
> eg ask 1800, got [7023:63]. Tried vbitrate=9000 , got [5677:63] No
> errors in log.
>
> Does that codec not support vbitrate? The HTML docs show a similar
> example.
Specifying bitrate should work, but it's not a good idea. If you plan
to transcode to mpeg4 later, you MUST have very high quality source
material, and that means you want constant qscale=2 (or at worst 3).
Rich
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