Hallo > However I have noticed, that during pure black mpeg2enc 1.6.1.90 uses > up to 1.4 Mbit/s no matter whether -q is 1, 4, 8 or 12. This I find strange. > The command line used is as follows: > > mpeg2enc -f 3 -g 6 -G 28 -b 5000 -q 12 -s -Q 2.0 -r 32 -I 1 -S 2000 -o > <filename> Have you tried it without the -Q flaog ?
> I hoped for - there being absolutely no change in the picture, that is > no motion nor AC coefficients to code, so all macroblocks could be > skipped - that pictures would end up being coded with, say, at most > several hundred bits. > Files sizes for one second of pure black: > 171261 bytes -q 1 > 171287 bytes -q 4 > 171287 bytes -q 8 > 171287 bytes -q 12 > (These sizes are so close to each other, I start to suspect some kind of > padding might be done on purpose here to prevent video buffer underruns?) When you multiplex the file home man I/P/B frames do you have ? Have you take a look after how many frames you have a new I frame ? you should see that with he default output options. (GOP start (15 frames)) There mpeg2enc also tells you also the average framesize. in my case it was always I: 9023, P/B: 9770 bytes. (PAL) > File size for one minute of pure black at -q 8 is 9890165 bytes (1.31 > Mbit/s). [Interestingly, gzip compresses this down to 1/93th: 106254 bytes.] Every I Frame has a specivic size mpeg2enc can't compress lower but any other programms can do. How did you generate pure black ? I did: lav2yuv test.eli | yuvscaler -I ACTIVE_4x4+0+0 | mp2enc -o test.mp2 I got a similar result for DVD size. > If I doing the math right, that makes six bytes per macroblock. > > Then I theoretized maybe handling pure black has problems, but I will > rarely have pure black areas in pictures anyway. Usually a black area in the image will help to save bits. > To test behaviour in the 'no change' case, I took one frame out of an > interview scene and duplicated it to make a clip, and encoded it with > the same settings. > > Files sizes for one second of 'no change': > 597014 bytes -q 1 > 164578 bytes -q 4 > 57688 bytes -q 8 > 37687 bytes -q 12 > > File size for one minute of 'no change' at -q 8 is 3321980 bytes (443 > kbit/s). > > 'No change' compresses to about one third of the size that pure black > compresses to! This is totally contrary to my expectations. :) > > I have uploaded the MPEG streams output by the above mpeg2enc runs for > further inspection here: > > http://andras.kadinger.hu/lomtar/mjpegtests/ > Could this probably point to a deeper issue? > Or am I approaching VBR the wrong way? No solution. Usually you have a lower bitrate for areas where you set to black. Instead of something that is near black. auf hoffentlich bald, Berni the Chaos of Woodquarter Email: [EMAIL PROTECTED] [EMAIL PROTECTED] www: http://www.lysator.liu.se/~gz/bernhard ------------------------------------------------------- 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
