[Libav-user] Encoding with variable frame rate

[Robert Krüger]

On Mon, May 20, 2013 at 4:27 PM, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:
> Robert Krüger <krueger at ...> writes:
>
>> >> > FFmpeg's mov muxer does not support vfr.
>> >>
>> >> Do you know what exactly is missing?
>> >
>> > No, but it was discussed recently on irc.
>
> (Maybe not recently or not on irc, sorry.)
>
>> OK, I am asking because in the code there is neither
>> a comment regarding that nor is it obvious that a
>> frame rate is used anywhere with the exception of
>> timecode tracks where it is needed for obvious
>> reasons and in mov_write_uuidprof_tag, which is
>> only used in PSP mode and the Quicktime spec AFAIK
>> offers no means of specifying a constant frame
>> rate explicitly.
>
> The point is that it will not try to write vfr files
> because the relevant flag is not set.
> (iiuc)
>
>> It will just result in a time-to-sample table that
>> looks differently if it is constant. But, of course,
>> there may be not so obvious places in the code,
>> where constant frame rate is assumed and for people
>> considering working on the mov muxer, this would be
>> valuable information. That's why I am asking. Is
>> IRC traffic archived publicly somewhere?
>
> http://ffmpeg.org/pipermail/ffmpeg-devel-irc/
> But I searched hard and couldn't find the (short)
> discussion I thought to remember ;-(
>
> This might help you:
> http://git.videolan.org/?p=ffmpeg.git;a=commit;h=91360ce
I see. But AFAICS this only makes the ffmpeg command line application
behave differently and not the muxer. So if I read baptiste's comment
right, it will work when used programmatically if timestamps start at
0 and maybe it is not too much work to make it work properly as soon
as someone really needs it, which is good to know.

Thank you,

Robert