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

[Marton Balint]

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