[FFmpeg-user] Duplicate frame when use seek option.

[tim nicholson]

On 25/09/14 22:16, Carl Eugen Hoyos wrote:
> tim nicholson <nichot20-at-yahoo.com <at> ffmpeg.org> writes:
> 
>> I have also found using vframes problematical in that 
>> you tend to get inconsistent mvhd and mdhd atoms unless 
>> you also use -shortest, while using -t is fine.
> 
> This doesn't sound familiar to me. Did you report this?
> 

We had a discussion on this a while back and there was a general
consensus that using frame counts could have issues, which is why I
switched to -t.

>> Trying to understand why it should need to duplicate a 
>> frame to get cfr though.
> 
> This is just the usual issue that the FFmpeg mov muxer 
> can't do variable frame rate.

Yes, looking at my source material, it seems like the first frame has a
non standard duration, which I guess ffmpeg is trying to 'correct', it
only seems to be an issue if you specify -ss 0, if you leave that option
off its fine.

The trouble is knowing if the duration figure is wrong, or the file
really has this duration anomaly on the front, and therefore which
setting is best to maintain av sync.

It seems to be a common issue at the front of files that were created
from video tape using a Pipeline. I have long been used to the cruft
they leave at the end, with the individual media streams being longer
than the flagged duration. It looks like they could do with some tlc at
the front as well...:(

> 
>> Sounds like it could do with a patch.
> 

Or maybe just a better understanding of what is going on, and the most
likely best parameters to get a satisfactory result.

> Certainly.
> 
> Carl Eugen
> 
-- 
Tim.
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