[FFmpeg-user] Optimise XDCAMHD422 Picture Quality - Syntax questions

[Chris von Görstinger]

Hello Marton,

I did use mdb bits and rt. But it didnt get better in my opinion. Maybe I
am too sensible for blocking artefacts.
mdb is my last option to improve the mpeg2 encoding. Right?


Am Di., 23. Okt. 2018 um 13:38 Uhr schrieb Marton Balint <cus at passwd.hu>:

>
>
> On Tue, 23 Oct 2018, Chris von Görstinger wrote:
>
> > Hello
> >
> > I am using this syntax to generate a XDCAMHD422 file:
> >
> > -c:v mpeg2video -r 25 -pix_fmt yuv422p -s 1920x1080 -aspect 16:9 -minrate
> > 50000k -maxrate 50000k -b:v 50000k -g 12 -flags +ildct+ilme -intra_vlc 1
> > -dc 10 -non_linear_quant 1 -bf 2 -qmin 1 -qmax 12 -top 1 -bufsize
> 17825792
> > -rc_init_occupancy 17825792 -rc_min_vbv_use 1 -rc_max_vbv_use 1
> > -sc_threshold 1000000000 -lmin "1*QP2LAMBDA" -vtag xd5c -color_range tv
> > -color_primaries bt709 -color_trc bt709 -c:a pcm_s24le -ar 48000 -f mxf
> > -timecode 12:34:56:11 -max_muxing_queue_size 1024 -metadata
> > "creation_time=2015-10-28T15:37:56"
> >
> > I mentioned by checking frame by frame with an editing tool (after
> effects)
> > that there are some frame with very much blockingess.
> > I tried with qmin/qman different values and surprisingly when using
> qmin=4
> > then the quality gets better.
> >
> > With qmin4 there are still tiny blocks (looks better than qmin=1), and I
> > now from other transcoders that the frames were these tiny blocks happen
> > CAN BE better encoded so that no blocks are visible for the whole GOP.
> > My questions are:
> > 1.) Why do I get a better quality with qmin=4 instead of qmin=1? -> Maybe
> > is datarate saved with qmin=4 which can be used for other frames were it
> is
> > needed more?
>
> That would be my guess too.
>
> > 2.) How can I improve the encoding a little bit more here in ffmpeg
> > regarding the picture quality?
>
> You can try using -mbd bits, it's going to be significantly slower, but in
> my experience it provides better quality.
>
> Regards,
> Marton
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