From: Tom B. <to...@ba...> - 2012-03-30 23:30:58
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Hi Scott, > > Chapter (really, any) boundary must be on a VOBU boundary. VOBU > boundary should be at an I frame. There shouldn't be more than one I > frame per VOBU, if so, your multiplexer sucks (use mplex from > mjpegtools -- the one I always tested/developed with). I think you mean one gop per frame, but, on the basis of what I've found and read, that is not a requirement: it is simply typically the case. A VOBU must contain between 0.4 and 1 second of playback. In one case, I've seen ffmpeg produce 5 I-frames in 0.32 second, and there's no indication that it thereby violates the DVD standard. > > Other "shoulds" include 2 B frames per P frame, minimum GOP length of > (I think) 9 frames, and max of (I think) 18 frames -- though that > might be NTSC dependent. "should" and "must" are not at all the same thing. My point is that dvdauthor allows the specification of chapter marker times, but evidently does not always apply them. It may be that dvdauthor cannot place the markers as specified if they do not align with VOBU boundaries in the input file, in which case, it should, at the very least, warn that it has not been able to comply with its instructions. On the other hand it may be that dvdauthor is intended to be capable of adjusting VOBU boundaries when necessary, so as to align with chapter markers, but fails, for reasons at present unknown, to do so, in which case it should be fixed. dvdauthor is an excellent tool that I've been using for years, but it seems there's a disconnect between an advertised feature and the ability to deliver it. > > (having the right number of B frames helps with hardware decoders that > won't FF/REW well if you only have I/P frames) True, but it doesn't help me put chapter marks where I want :-) Tom. |