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November 23, 2008
audio has frames too
tiki sent me his new mm6 run today in dvd format and i was dismayed to notice that it apparently had random audio desync after indexing using dgindex (with the audio leading the video). the vobs played fine in e.g. mplayer, so i wasn't sure whether his dvd recorder was making a new chapter and chopping up the audio every few minutes or what.
after several hours of playing around, my initial guess turned out nearly correct: the "Skipping frame!" messages i was seeing every few hundred frames from mencoder trying to transcode the file were because the audio was bad, not the video. actually, i should have known this from the start - if it had been the video, then the video would have been leading the audio, not vice versa as i initially observed at points. i had also forgotten that the term "frame" also applies to many audio formats. using mencoder's -noskip option together with the -mc 0 option seemed to restore a semblance of audio sync in an nmf - enough to carefully stretch the audio to correct the progressive desync to an acceptable level.
tiki has been advised of the situation. right now we are guessing it was because he used rf (from his nes). pal nes is known to generate a nonstandard signal (enough to cause massive frame droppage with more sensitive capture devices), so maybe the ntsc nes in combination with rf confused his dvd recorder? i'll post again as i learn more.
Posted by njahnke at November 23, 2008 8:59 PM
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