Re: Pulsating at I frames with Mpeg2 Video

--- Rich Felker <dalias@xxxxxxxxxx> wrote:

> On Fri, Apr 14, 2006 at 10:16:51AM -0700, Dan Gelb wrote:
> > I'm having a problem with a pulsating effect appearing when I
> create
> > Mpeg2 videos using FFmpeg. It seems to be happening at the I
> frames,
> > resulting in blocking artifacts that appear every time there is an
> I
> > frame. Reducing the bitrate results in worse pulsating. I've
> uploaded
> > two example output videos to:
> > 
> > ftp://ftp.mplayerhq.hu/MPlayer/incoming/mpeg2pulse/container.mpg
> > ftp://ftp.mplayerhq.hu/MPlayer/incoming/mpeg2pulse/akiyo.mpg
> > 
> > For the container.mpg video the pulsating is most visible in the
> water.
> > I've set the gop size to 30 so that the pulsating happens every
> second.
> > Here are the arguments I used to create the video:
> > 
> > ffmpeg -s 352x288 -i container.yuv -bufsize 44 -b 500 -minrate 250
> > -maxrate 500 -g 30 -vcodec mpeg2video container.mpg
> > 
> > For the akiyo.mpg file the pulsating is most obvious towards the
> end of
> > the video. The arguments I used for the akiyo video are:
> > 
> > ffmpeg -s 352x288 -i akiyo_cif.yuv -bufsize 22 -b 250 -minrate 250
> > -maxrate 250 -g 30 -vcodec mpeg2video akiyo.mpg
> 
> I have options to work around this bug for mencoder:
> 
> -lavcopts vi_qfactor=0.1:vi_qoffset=1.5:
> 
> Using the equivalent options for ffmpeg might do the trick. This is
> not a correct fix, but a mostly-ok workaround.
> 
> Rich
> 

Thanks for that information. It helps for some of the sequences I've
tried, but there is still noticeable pulsating with most of them. You
mentioned that it is only a workaround. Is this pulsating, or changes
in quantizer from I to P frames, a known bug? Should I report this
problem on the ffmpeg-devel mailing list?

Dan