[XviD-devel] What B-frames give

[Michael Militzer]

Hi,

> I updated my p/b/i decision and did some more tests.
> I-frame decison is now based on the old sad/deviation comparsion and
> works very good - just as good as the old ME-based version. I'm not
> going to play anymore with it, if someone writes something better
> (like histogram-based) then great.
>
> As for P/B decision, I tried sum of squared SADs again (it just looks
> so much more logical to me) but it gave me worse results - so it stays
> the way it was yesterday.
>
> Some tests. All testes were made with dvd-resolution and noisless
> (compared to vhs) clips.
> I encoded them at fixed quant of 3, with b-frame ratio=134% (quant 4 -
> I hope) and compared filesizes:
>
> 1. matrix lobby
> max_frames = 0 : 23857 kb
> max_frames = 1 : 21197 kb
> max_frames = 2 : 20783 kb
> max_frames = 3 : 20754 kb
>
> 2. warcraft III trailer
> max_frames = 0 : 22659 kb
> max_frames = 1 : 20240 kb
> max_frames = 2 : 19894 kb
> max_frames = 3 : 19873 kb
> max_frames = 4 : 19904 kb
> max_frames = 5 : 19947 kb
>
> 3. a bit of anime (taken directly from divx so the test isn't very
>    serious)
> max_frames = 0 : 12710 kb
> max_frames = 1 : 11638 kb
> max_frames = 2 : 11159 kb
> max_frames = 3 : 11098 kb
> max_frames = 4 : 11112 kb
> max_frames = 5 : 11157 kb
>
> The visual quality of b-frame encodings is a bit higher imho (!)
> because I don't see any smearing artifacts. I don't see any
> degradation of b-frames' quality (well the quantizer is a bit higher
> after all) either.
>
> The file increase with max_bframes -> infinity shows that my P/B
> decision is not perfect - a perfect one wouldn't allow any file
> increase when given less limitations.
>
> What do you think?

I like the results. It would be good if the decision criteria could be
further improved so that the files won't get bigger anymore for high
max_bframes settings, but nonetheless I think the variable b-frame approach
is surely superior to simple constant b-frames behaviour...

Michael