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

[Tom Evans]

On Thu, Sep 5, 2013 at 3:23 PM, James Board <jpboard2 at yahoo.com> wrote:
> The documentation doesn't mention that image2 is a CFR muxer and that
> it will duplicate and/or drop images from the input video in order to achieve
> some CFR.  I'd suggest the documention should mention that since it happens
> 'behind the scenes' and there's no way for a new user to know or predict that
> will happen.

It sort of does actually:

http://ffmpeg.org/ffmpeg-all.html#image2-1

All the examples include a fixed output frame rate, and all explicitly
list the "-vsync 1" setting, "-vsync 1" being an alias of "-vsync
cfr".

>
> It will also be nice if the image2 muxer and the select filter handled frame numbers
> consistently.  I understand that different people want the default behavior to do different
> things.  That's okay with me.  But if the image2 muxer is telling me that frame
> 100 is one thing, and the select filter interprets frame 100 as another thing, then
> that is a problem for me, and I'd consider that a bug.

What the image2 muxer produces as frame 100 is the 100th frame of the
CFR output. What the select filter filters on is the 100th frame of
the VFR input.

>
> If most people want ffmpeg to behave that way, then that's okay.  It's your product.
> Then I think my best option is to produce a sequence of image files, edit that sequence directly,
> then produce the output video directly from the individual files: no image2 muxer,
> and no select filter.

"Produce a sequence of image files" is what the image2 muxer does. It
takes video frames and muxes them to an image sequence.

>
> Thanks for explaining everything to me.

No probs

Cheers

Tom