[x264-devel] Question on keyint_min and open gop

[BugMaster]

On Thu, 5 May 2016 15:40:13 +0000, Li, Stephen wrote:
>   
> Hi,
>
> I am wondering what is the effect of keyint_min when open gop is
> enabled. From what I understand, keyint_min affects whether an
> I-frame or IDR-frame should be used when a scene cut is detected.
> But in open gop, there are no IDR frames.  It seems to make sense
> that keyint_min should have no effect. But based on my testing, the
> output bitstream is quite different when different keyint_min is used.
>
> Any ideas?
>  

Use of open gop doesn't mean there is no more different between simple
I-frames and I-frames that are key-frames (recovery points). There is
still scenecut detection which decide which frame should be key-frame
which is influenced by keyint_min. With simple I-frame *any*
subsequent frame (be this P or B-frame) can reference frames before it
while they still in DPB. With open gop key-frames (also I-frames) the
only frames that can reference before it are B-frames which directly
follow this key-frame in decoding order (i.e. have latter DTS) and
which in presentation order precede it (i.e. have earlier PTS). Also
open gop key-frames need write recovery point SEI which simple
I-frames don't.