[Ffmpeg-devel] MPEG 2 Quality Issues
Thu Nov 30 10:40:35 CET 2006
Brian Brice wrote:
> A while back I had emailed about bitrate issues regarding MPEG 2
> encoding, and now I'm back for quality issues! I have a DV clip
> that contains some fast motion and I'm getting some horrible blocking
> when trying to encode to MPEG 2. I am trying to find the right options
> to pass to ffmpeg that make a huge different in the quality of the
> encoding. I've used TMPGEnc and it produced *great* results, and I wish
> I could get ffmpeg up to the same standard. At this point I'm just
> passing numbers without knowing what they do.
> I have tried setting lmin to 0 and lmax to 1*QP2LAMBDA. This video
> smooth like I would expect, but the bitrate ended up averaging around
> 13.7 Mbps even though I tried to aim for CBR 7 Mbps.
> Here's a sample screenshot of how TMPGEnc looks to ffmpeg:
> TMPGEnc: http://heapify.org/etc/ffm/tmpgenc.png
> ffmpeg: http://heapify.org/etc/ffm/ffmpeg.png
> Major blocky-ness with ffmpeg :-(
> Here is the original clip:
> Encoded with ffmpeg without lmin/lmax settings:
> Encoded with TMPGEnc, looks *great* as I want ffmpeg's to :-(
> Here is how I used ffmpeg:
> ffmpeg -i TestforMPG-Short.avi -y -f vob -vcodec mpeg2video -acodec mp2
> -ab 384k -ar 48000 -ac 2 -aspect 4:3 -b 7000k -minrate 7000k -maxrate
> 7000k -bufsize 1835008 -g 12 -bf 2 -flags ildct+trell -mbd 2
> I know ffmpeg is capable of having decent quality at 7 Mbps, but how can
> I achieve this? TMPGEnc does it, how can ffmpeg? Any advice,
> recommendations, information is greatly needed and appreciated. Thank
> you guys.
ffmpeg -i TestforMPG-Short.avi -vcodec mpeg2video -minrate 7000k
-maxrate 7000k -b 7000k -bufsize 5000k -bf 2 -flags +qprd+ildct -flags2
+ivlc+sgop -mbd rd -sc_threshold 10000000 -lmin 1 -mblmin 1 -lmax
'340*QP2LAMBDA' -f vob -ab 192 ffmpeg.mpg
Feel free to add +trell.
You must know that every encoder around WILL activate qprd. You can
detect it by using -debug 16, if macroblocks have differents values then
qprd is activated.
Always try to use the largest bufsize for rc, the bigger buffer is, the
more rc will be efficient.
Baptiste COUDURIER GnuPG Key Id: 0x5C1ABAAA
SMARTJOG S.A. http://www.smartjog.com
Key fingerprint 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA
Phone: +33 1 49966312
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