HI Jay, > My question now concerns optimizing for quality. I watched a couple of > the SVCDs I'd burned recently, and while overall the quality was fine, > on one of the discs had many dark scenes, and these tended to get badly > pixelated. ? > What can I do to improve output quality, given the constraints of the > SVCD format? The discs described above were actually converted using my > old pipeline, which used an mjpeg lav file as the intermediate step > between divx and mpeg2, so I'm curious if that extra codec might be > responsible for the lower quality in the dark scenes. Also, is there > any advantage to lowering the audio bitrate (I'm using 192 now), i.e. > does it free up for bots for video or just make the file smaller. Is > there anything else I can do to get the best quality SVCDs?
There are several possibilities here: 1. Someplace in the chain an incorrect colour-space or gamma conversion may be taking place. 2. The long encode/decode chain won't help. You're accumulating quantisation noise at each decode/encode stage. This is especially bad if you are changing resolution along the way. If you can do it try to avoid that middle stage of going to MJPEG and go direct from DivX to YUV4MPEG. 3. The eye is most sensitive to quantisation in dark shades. The quality is actually the same throughout but you simply *notice* the quality problems in the dark scenes. One optimisation I want to add to mpeg2enc is to automatically reduce quantisation (if possible) in darker scenes. 4. SVCD is actually a very bit-rate limited format. 2500Kbps is actually pushing MPEG-2 pretty hard. However, many DVD players can happily play over-speed SVCD. Mine goes fine with 3800Kbps video (it can probably do more but that is the most I've bothered to try). This gives MPEG-2 much more headroom for difficult to encode scenes. The trick is to set a fairly high peak bitrate but a relatively conservative quality floor (-q). This means the bits only get used when the going gets tough for the encoder so overall compression stays high. For SVCDs I tend to use: -f 5 -q 6 -b 3300 Andrew PS It would be mega-fantastic if we could tweek the drivers to capture MJPEG at SVCD resolution. I think the Zoran chipset / video decoders can actually support this. The necessary driver tweaking would be pretty fiddly though... ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ Mjpeg-users mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/mjpeg-users
