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

[Emmanuel Weber]

Thanks for the quick reply.
I do have some VBV caps but I figure I would send the simplest command
line that reproduce the issue.
I am indeed using 1-Pass ABR. I will experiment with CRF.

Emmanuel

On Sun, Oct 10, 2010 at 2:39 PM, Jason Garrett-Glaser
<darkshikari at gmail.com> wrote:
> On Sun, Oct 10, 2010 at 2:33 PM, Emmanuel Weber <weberemmanuel at gmail.com> wrote:
>> 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
>
> Using 1-pass ABR mode is strongly discouraged; it's not well-optimized
> and has many issues like these.  If you're in a zero latency
> environment, you almost surely need some sort of VBV caps, and you
> probably want to be using CRF mode instead.
>
> Dark Shikari
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