On Sunday 29 June 2003 05:31, Ronald Bultje wrote: >Hey Ron, > >On Sun, 2003-06-29 at 06:41, Ron Keller wrote: >> I am puzzled by the performance of my Studio DC10plus capture >> card. using lavrec (from mjpegtools-1.6.1), I don't LOSE frames, >> but frames do get INSERTED - at the rate of 15 per hour. I have >> played with buffer_size and buffer_number; and also with quality >> of the capture video. I don't see any noticeable A/V sync >> errors, but I am curious as to why these extra frames arew being >> inserted. Are you able to answer this for me? Thanks > >It's for keeping synchronization. We program the audio clock and the >video clock at a certain rate (say, 25 fps and 44,1kHz) but they > will slightly differ (this is mostly the audio clock, which is > ususlaly not 100% correct). Normally, this means that video/audio > would drift apart and you'd get wrong synchronization (voice coming > one second after video person moves his mouth, that kind of > things). We use software frame inserting/dropping to correct for > this. So once in a while, it drops or inserts a frame so that the > video and audio clock drift are corrected for. > Thanks for clarifying that. I hadn't made that connection in my mind, mainly because our major loss of A/V sync comes from using framestores to synchronize everything to the local references, making the video late by a frame per framestore in the circuit. >Nothing to worry about, you basically don't see it in the end result >anyway. :). > >Ronald -- Cheers, Gene AMD K6-III@500mhz 320M Athlon1600XP@1400mhz 512M 99.26% setiathome rank, not too shabby for a WV hillbilly Yahoo.com attornies please note, additions to this message by Gene Heskett are: Copyright 2003 by Maurice Eugene Heskett, all rights reserved.
