[FFmpeg-devel] [RFC] Frame rate emulation

[Ramiro Ribeiro Polla]

Hello,

x11grab provides its own frame rate emulation inside its read_frame 
function. Many other grab formats will need it (GDI, VFW...), so it 
would be best to make a format level frame rate emulation in FFmpeg, and 
not each demuxer (also I believe they don't belong in the demuxers 
themselves).

FFmpeg already provides a frame rate emulation (added for DV), but it 
works depending on a codec's demand, and not at a format level, like 
avcodec.h says:
    /**
     * Frame rate emulation. If not zero, the lower layer (i.e. format 
handler)
     * has to read frames at native frame rate.
     * - encoding: Set by user.
     * - decoding: unused
     */

It's in Fabrice's TODO "suppress rate_emu from AVCodecContext".

I don't know DV's needs for rate emulation, but couldn't it be passed to 
ffmpeg.c's AVOutputStream instead of AVCodecContext? It would depend on 
the format then, and not the codec.

Also, I plan to add that to AVInputStream, right before av_read_frame, 
where it will be useful for grabbing demuxers.

Can there be 2 places where rate emulation occurs (reading from the 
format, and writing to the codec)?
Is it ok for DV for the rate emulation to occur at writing to the output 
format, so it's checked in AVOutputStream?

Ramiro Polla