[FFmpeg-devel] Scalable Video Encoding and FGS

[Erik van Zijst]

Michael Niedermayer wrote:
> On Thu, Oct 11, 2007 at 12:27:17PM -0700, Erik van Zijst wrote:
>> I think streaming video could also benefit from this platform/protocol 
>> when you apply some form of scalable encoding: have a small base-layer 
>> and multiple enhancement layers. I've looked at MPEG2 FGS which comes 
>> closest to my needs, but this has not been implemented in any serious 
>> codec AFAIK.
> 
> no, and i think almost everyone is very glad that it hasnt, same for the
> equivalent mpeg4 scalability stuff
 > [...]
> also maybe b frames provide already enough scalability for your needs
> and they are fully supported on all decoders

I've considered layering on frame-type again (also comes up a lot in the 
research community), but I don't think it will be able to lower the 
bitrate significantly due to their relative sizes.

In MPEG1 b-frames are roughly 70 times smaller than i-frames [1], so 
cutting the bitrate in half, requires removal of 70 b-frames per i-frame 
(sure, these figures old and mpeg1-specific, but what matters is the 
concept).

So frame removal could be used to gain some scalability, but IMHO it 
cannot match the granularity of FGS and SVC.

[1]
"The typical data rate of an I-frame is 1 bit per pixel while that of a 
P-frame is 0.1 bit per pixel and for a B-frame, 0.015 bit per pixel." -- 
http://bmrc.berkeley.edu/frame/research/mpeg/mpeg_overview.html

Erik
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