[FFmpeg-user] Image extraction broken with ffmpeg, but not with mencoder. How can I fix this?

[Paul B Mahol]

On 9/4/13, James Board <jpboard2 at yahoo.com> wrote:
>>> My question is: what does -vsync do?  And, why does it work (so
>
>>> I can avoid this problem in the future)?
>>>
>>
>>See http://ffmpeg.org/ffmpeg.html and search for vsync. All the answers
>>to your present and past problems are there.
>
> Already did that.  This is what it says about -vsync 0:
>
>     `0, passthrough'
>     Each frame is passed with its timestamp from the demuxer to the muxer.
> So why does ffmpeg duplicate frames when I don't use '-vsync 0'.  And
> why does it not duplicate frames when I use '-vsync 0'.  Why does it matter
> what timestamps is passed to the muxer?  I'm generating individual files as
> output so why does the timestamp matter?

If input frame rate is smaller than output frame rate, ffmpeg will create
extra frames by default.

If input is vfr and output is cfr than it may duplicate and/or remove frames.