[Ffmpeg-devel] Re: getting the frame-rate

Rich Felker dalias
Thu Aug 25 23:31:44 CEST 2005

On Thu, Aug 25, 2005 at 05:44:23PM +0200, IOhannes M Zmoelnig wrote:
> Burkhard Plaum wrote:
> >For some formats, the framerate isn't constant, so even if you'll get some
> >value for it, it will be meaningless. At least for asf, rm and mov/mp4, 
> >there is no other possibility than to use the individual timestamps
> >of the frames.
> i do not think that this is a valid argument.
> most formats do have a constant framerate (i think); those with an 
> unknown or variable framerate could return an error-value or an invalid 
> framerate (like -1)

All formats have a time base, which may or may not correspond to
framerate. This is the most you can know.

> what happens if there are formats that do not have a constant image-size 
> any more ? will you remove the dimension-information from the API ?? 

No. If it were a real issue, the image dimension information would be
generalized in such a way as to _handle_ changing dimensions. (In such
a stupid hypothetical situation...) Similarly this is what happened
with framerate. The concept of framerate was generalized to time base
in order to handle video without a framerate while still providing
maximal information when there is a framerate.

> (mpeg4 provides arbitrary shapes. whether it also provides a means to 
> change this shape in time, i dunno)

This is nonsense that's outside the video part of mpeg4.


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