[x264-devel] Issue when encoding a sequence that starts with a static image

[Emmanuel Weber]

Hi,

I am trying to encode some sequences which start with a static image
followed by some video content.
The static image is displayed for several seconds and then the video starts.

What is happening is that all the frames after the IDR and until the
first frame of the video sequence are encoded fully with SKIP MBs. The
static image appear blurry and is never improved even though there are
bits available.

This is done using the zerolatency, superfast preset and baseline
profile (it seems the problem happens with other presets as long as
zerolatency is used).

Using the cli, my command line looks as follow:
--tune zerolatency --preset superfast --profile baseline --bitrate
1500 --ref 1 -o test.264 --input-res 1280x720 test.yuv

In order to reproduce you just need to generate a sequence containing
the same frame repeated many times.

I have looked at the code, and it seems that in the get_qscale
function, we fall in the case where no texture bits and no mvbits have
been generated so we use the previous q value which in turn cause the
next frame to be encoded fully with SKIP MB etc

Thanks,
Emmanuel