Re: Chapter marks not where specified.

Hi Lawrence,
> 
> > 1149.32   1149.00 This five I-frames early!
> 
> If you have 5 I-frames in the space of 0.32 of a second, that sounds
> like an awful lot of I-frames.

I had thought that myself.

> Would I be right in saying that all the
> discrepancies are less than 0.5 seconds?

Indeed.  The statistics are curious, given that the chapter marks ought to be 
random with respect to VOBU boundaries.  The distribution of errors is very 
odd, almost uniform in the negative direction with the single 5-frame positive 
standing out like a sore thumb.

> Because remember what I said
> elsewhere about VOBU boundaries, and checking some FFmpeg-converted
> MPEG footage I happen to have lying handy seems to indicate that VOBUs
> are typically about 0.5 seconds in duration.

Hold the bus!  All the I've read says that chapter marks must be I-frames, 
with no mention of also having to coincide with the start of VOBUs; indeed, 
how would one be supposed to ensure this?.  I realize that VOBUs are the only 
addressable objects on a DVD, and had assumed (there I go again) that when 
dvdauthor said it was "fixing VOBUs" that it was ensuring that the a new VOBU 
starts at each chapter mark.  If this is not the case, then, surely, trying to 
specify chapter marks with any precision is entirely futile unless ffmpeg 
implement a -force_vobu_boundary' option instead of '-force_key_frames', which 
is rendered useless.

Clarification would be *extremely* welcome.

Tom.



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