[x265] Artifacts with vbv-init/vbv-end

[Diego Pasqualin]

Hi Alex, sorry to bother, could you please just confirm whether
--frames:v or -x265-params "frames=N" should indeed be passed and
recognized by x265?
I could open a ticket on ffmpeg github.

Thank you.

Em qui., 29 de out. de 2020 às 20:43, Diego Pasqualin <dpasqualin at gmail.com>
escreveu:

> Hi Alex, thank you for your reply,
>
> I tried 0.9 and got the same issue. In fact I even tried without
> segmenting the video, just adding vbv-init and vbv-end and encoding the
> entire video at once.
> vbv-end-fr-adj can only be enabled if the total number of frames is known.
> The '--frames' option seems to be CLI only (see below), and the '-frames:v'
> from ffmpeg is not recognized by x265 (shouldn't it be?).
>
> If I try to use frames=15866
> [libx265 @ 0x49c7240] Unknown option: frames.
>
> If I try to add -framed:v to ffmpeg:
> x265 [error]: vbv-end-fr-adj cannot be enabled when total number of frames
> is unknown
>
> Em qui., 29 de out. de 2020 às 19:34, Alex Giladi <alex.giladi at gmail.com>
> escreveu:
>
>> Hi Diego,
>> I would try 0.9 as opposed to 0.5 on both vbv-init and vbv-end.
>> There is also an optional --vbv-end-fr-adj parameter, you may want to
>> play with it. May want to tune it, 12+ frames is best at hiding the
>> stitch point.
>> Best,
>> Alex.
>>
>> On Thu, Oct 29, 2020 at 12:23 PM Diego Pasqualin <dpasqualin at gmail.com>
>> wrote:
>> >
>> > Hi, I'm revisiting some parameters in our chunked encoding pipeline and
>> I stumbled upon vbv-init and vbv-end, which seems to be recommended for the
>> use case (https://x265.readthedocs.io/en/3.1/cli.html#cmdoption-vbv-init).
>> However, if I set these two parameters I get really bad artifacts,
>> strangely more intense in the right bottom part of the output video. I took
>> this screenshot as example https://pasteboard.co/JxVhD78.png
>> >
>> > This is the full ffmpeg command. If I remove the vbv-init/vbv-end it
>> encodes nicely without artifacts. Any idea on what might be going on? Thank
>> you very much!
>> >
>> > ffmpeg -fflags +genpts -i big-buck-bunny.mp4 -map 0:v -bf 3 -refs 3
>> -crf 21 -force_key_frames expr:gte(t,n_forced*2) -g 50 -keyint_min 50
>> -x265-params
>> "hrd=1:vbv-init=0.5:vbv-end=0.5:vbv-maxrate=1870:vbv-bufsize=3740:keyint=50:min-keyint=50:no-open-gop=1:bframes=3:ref=3:level=40:limit-modes=1:rect=1:amp=1"
>> -c:v libx265 -flags +cgop -map_chapters -1 -map_metadata -1 -pix_fmt
>> yuv420p -preset medium -profile:v main -r 25 -vsync cfr -sws_flags bicubic
>> -filter:v scale=trunc((oh*iw*sar/ih)/2)*2:720 -an -dn -sn -y ./output.mp4
>> > _______________________________________________
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>
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