[FFmpeg-user] (no subject)

[Reuben Martin]

On Monday, April 17, 2017 6:22:18 AM CDT Erik Slagter wrote:
> > according to mp4box tutorials that I have read about making mpeg-dash, I
> > know that I have to set keyint and minkey int equal and also related to
> > segment duration. so I tries using min-keyint=100, but the result video
> > had
> > the min-keyint=51
> 
> Do the tutorials also explain why you would ever want to use a braindead
> (!) fixed gop size in the first place?
> 
> I could imagine a requirement for a closed gop type, but really not why
> you'd want to be gop's always exactly the same length, it's making
> encoding really inefficient.

If you encode a DASH stream with multiple representations (dynamic streaming 
with multiple resolutions / bitrates) you have no way to ensure that the 
encoders for the different resolutions and / or bitrates set the exact same 
GOP boundaries and segmentation on the same frames. Without some way to slave 
encoder processes to one master encoder process with respect to GOP, frame-
type decisions and segmentation, locking down the GOP to a set size is the 
only way to ensure that.

Would be awesome if ffmpeg / x264 developed a way to provide that master - 
slave IPC between different encode sub-processes.

May not apply to this specific situation, but I think that is the thinking 
behind the strict GOP size recommendation.

-Reuben