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

Chris von Görstinger christophgerstbauer at gmail.com
Tue Oct 23 11:34:38 EEST 2018


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

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?
2.) How can I improve the encoding a little bit more here in ffmpeg
regarding the picture quality?


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