[FFmpeg-devel] Scalable Video Encoding and FGS
Erik van Zijst
ffmpeg
Fri Oct 19 20:44:17 CEST 2007
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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