Heyo, I recently had a discussion with Jonas about the usage of vqscale in the first pass of a two pass encoding. So i wanted to test it and got following results: Source: VIDEO: [MP43] 320x240 24bpp 23.98 fps 615.4 kbps (75.1 kbyte/s) --- 1.pass: vbitrate=615 / 2.pass: vbitrate=615: 1.pass: -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vpass=1:vbitrate=615 2.pass: -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vpass=2:vbitrate=615 Video stream: 615.120 kbit/s (76889 bps) size: 381096793 bytes 4956.394 secs 118836 frames Audio stream: 128.000 kbit/s (15999 bps) size: 79295296 bytes 4955.956 secs PSNR: Y:44.30, Cb:47.20, Cr:47.93, All:45.14 --- --- 1.pass: vqscale=5 / 2.pass: vbitrate=615 1.pass: -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vpass=1:vbitrate=615:vqscale=5 2.pass: -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vpass=1:vbitrate=615 Video stream: 615.094 kbit/s (76886 bps) size: 381080897 bytes 4956.394 secs 118836 frames Audio stream: 128.000 kbit/s (15999 bps) size: 79295296 bytes 4955.956 secs PSNR: Y:44.02, Cb:46.98, Cr:47.74, All:44.87 --- Now, the two results seem to be pretty much the same from size and PSNR, but a analysis plotpsnr.pl shows, that the second test (with vqscale) has the quantisizer size most time at 4 and less (just a few times at the beginning at 5 and 6) while the first test has it at 5 and less. If i'm not mistaken, then the file size and the quality of an encoding is mostly dictated by the used quantisizer values (assuming that the same MVs are choosen) But why is there so less difference in the file size (beside the file with the lower quantisizer is smaller!) and why doesnt the PSNR differ at all ? Can anyone explain that ? I uploaded the two psnr logs, if you want to have a look at them: http://people.ee.ethz.ch/~adogan/psnr_vbitrate.log.gz http://people.ee.ethz.ch/~adogan/psnr_vqscale.log.gz Attila Kinali -- Emacs ist für mich kein Editor. Für mich ist das genau das gleiche, als wenn ich nach einem Fahrrad (für die Sonntagbrötchen) frage und einen pangalaktischen Raumkreuzer mit 10 km Gesamtlänge bekomme. Ich weiß nicht, was ich damit soll. -- Frank Klemm, de.comp.os.unix.discussion