[Ffmpeg-devel] Strange behaviour of jpeg & qscale

[Rich Felker]

On Fri, May 06, 2005 at 10:09:11PM -0400, Philip Gladstone wrote:
> I've been fiddling with ffserver a bit recently, and it is happier than 
> it was. However, I uncovered a strange feature of encoding to jpegs.
> 
> The commands
> 
> ffmpeg -vd /dev/video0 -qscale 25 -s 320x240 -f singlejpeg -vframes 1 
> -dct_algo 1 qs25.jpg
> 
> ffmpeg -vd /dev/video0 -qscale 25 -s 320x240 -f singlejpeg -vframes 1 
> -dct_algo 3 qs25.jpg
> 
> behave very differently. The first produces a good jpg image. The second 
> has some serious problems. This is with the latest CVS sources, built on 
> Linux on Athlon.
> 
> I do not have enough DCT-fu (nor MMX fu) to figure out what is going 
> wrong. Note also that when the dct_algo is not defined, it automatically 
> chooses (I think) 3, and thus generates the busted image.

I dunno, but qscale=25 is horrible quality... You probably want
qscale=2 or 3 at the highest.

Rich