From: Steven M. S. <sms@2BSD.COM> - 2003-07-29 23:48:11
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On Wed, 30 Jul 2003, Steffen Barszus wrote: > Sorry if I break the thread, but is there any straight relation between > average bitrate and -q values? Not really - at least not that I know of. -q causes the VBR logic to be used (without -q mpeg2enc will generate CBR streams). The value to -q tells the encoder how hard to push the Average bitrate up against the Maximum (specified by -b). If the average rate becomes too close or exceeds the maximum then the encoder must lower the quality in order to keep under the maximum rate. Thus specifying a -q value too low actually decreases quality ;( > A rule of thumb one could apply? There are a couple rules of thumb (two thumbs = two rules :) :)) I use: 1) -q 4 is the lowest value to use (sometimes 5 or 6 is adequate) and 2) try to keep between 10% and 20% difference between the average and peak bitrates. Doing a shor test encoding starting with -q 6 is a good idea (especially if the actual encoding run will take 8 or 10 hours ;)). Then look at the average and max rates. If they are not too close then decrease '-q' by 1 and try again. If the values are less than 10% apart then increase -q by 1. > Sounds very interesting whats going on lately on the list :)) Yes, it's been quite fascinating (interesting too ;)). Cheers, Steven Schultz |