[FFmpeg-user] problem of transcoding HD DVB-T program

Andy Furniss adf.lists at gmail.com
Tue Jun 17 19:01:22 CEST 2014

Soundwin / Andy wrote:
> Thanks a lot.
> I modify the DVR_BUFFER_SIZE of drivers/media/dvb/dvb-core/dmxdev.h
> to original (10*188*1024) due to dvb will drop the whole buffer if it
> fills.
> I found that using dvblast can prevent this issue, including "Value
> too large for defined data type" problem which I doesn't mention
> before.

That's good, though looking at you command -

home/andy/ffmpeg -f mpegts -i pipe:0 -c:v libx264 -preset medium -crf 23
-bufsize 3000K -minrate 1200k -maxrate 1200k -pix_fmt yuv420p -g 50 -s
1024x768 -acodec libmp3lame -b:a 128k -ac 2 -ar 44100 -f mpegts
udp:// &

I don't think crf and fixed rate are supposed to go together.

The biggest issue I think you will have is the resizing. If the content
is interlaced then you will be scaling down weave and it won't look
good, or be able to be deinterlaced.

Of course a lot of broadcast is progressive, so that will be OK.

It is possible to detect and control a de-interlacer before the recode,
but it will add more cpu usage.

You could do an interlace aware scale - but I don't know how much that
would mess  up progressive, or if it's possible to change the scale on
the fly depending on the content.

I am not sure there are easy solutions if you have to scale down and are
short of cpu.

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