Re: [rtcweb] H.261 encoding samples at typical bitrates - sign language example

[Gunnar Hellstrom <[e-mail]>]

The 289 kbit/s is clearly usable for sign language without problems. The 
fingers are clearly visible, the mouth shape and the eye-gaze direction.
If that was done with 25 fps it is good and sufficient. Never lower 
frame-rate below 20 fps!

With the size of the person, two persons could be fit into the same 
picture and still be good.

That matches the old observations from mid-90-s with the best conference 
units.

( the 541 kbit/s looks a bit overdone in artificial sharpening or 
something. Not as good as the 289. )

Gunnar

On 2013-12-05 22:21, Justin Uberti wrote:
> A frame comparison for the various encodings:
>
>
> On Thu, Dec 5, 2013 at 1:05 PM, Justin Uberti <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>     Ow, my eyes...
>
>     The 256 kbps and lower clips are unusable. The 512 kbps clip is
>     borderline, but might be usable if the framerate was cut in half.
>
>     Remember also that these test clips are far better than what would
>     be obtained from consumer webcams (i.e. good lighting, no shake,
>     no temporal noise), so real-world performance is likely to be
>     worse than what you see here.
>
>
>     On Mon, Dec 2, 2013 at 8:23 PM, Basil Mohamed Gohar
>     <[e-mail] <mailto:[e-mail]>> wrote:
>
>         On 12/02/2013 10:03 PM, Basil Mohamed Gohar wrote:
>         > Let's let any further discussions about the usability of
>         H.261, or any
>         > other codec for that matter, use actual examples going forward.
>         >
>         > The following is a VERY quick test of ffmpeg's h261 encoder
>         in the
>         > context of the IETF's rtcweb working group's discussion of
>         an MTI
>         > (mandatory-to-implement) video codec.
>         >
>         > sine_irene_cif.y4m taken from derf's collection:
>         >
>         > http://media.xiph.org/video/derf/y4m/sign_irene_cif.y4m
>         >
>         > ffmpeg version N-58565-gc122e69
>         >
>         > bitrate=64k,128k,256k,512k
>         >
>         > ffmpeg -i sign_irene_cif.y4m -codec:v h261 -b:v $bitrate -g 30
>         > sign_irene_cif.y4m-$bitrate.h261
>         >
>         > http://media.basilgohar.com/rtcweb/sign_irene_cif.y4m-64k.h261
>         > (real rate: 157.8kbits/s)
>         >
>         > http://media.basilgohar.com/rtcweb/sign_irene_cif.y4m-128k.h261
>         > (real rate: 165.6kbits/s)
>         >
>         > http://media.basilgohar.com/rtcweb/sign_irene_cif.y4m-256k.h261
>         > (real rate: 289.5kbits/s)
>         >
>         > http://media.basilgohar.com/rtcweb/sign_irene_cif.y4m-512k.h261
>         > (real rate: 541.8kbits/s)
>         >
>         > I apologize for the bitrate inflation, but if I had more
>         time I can
>         > tweak the settings for a more accurate number.  These are
>         simply the
>         > rates that ffmpeg produced with such a short clip at the
>         given requested
>         > rates.
>         >
>
>         I've updated the encoding settings as follows to get more accurate
>         resulting bitrates, but ffmpeg's h261 encoder seems to
>         bottom-out at
>         around ~140kbps, so the only examples from above that are
>         close (after
>         using the new settings) are 256k and 512k.
>
>         for bitrate in {1..512}k; do ffmpeg -i ../sign_irene_cif.y4m
>         -codec:v
>         h261 -b:v $bitrate -minrate $bitrate -maxrate $bitrate
>         -bufsize $bitrate
>         -qmax 1024 -g 30 -y sign_irene_cif.y4m-$bitrate.h261; done;
>
>         All the above posted examples can be viewed with mplayer and a
>         bash
>         command line using the following, if you're interested:
>
>         mplayer
>         http://media.basilgohar.com/rtcweb/sign_irene_cif.y4m-{64,128,256,512}k.h261
>         <http://media.basilgohar.com/rtcweb/sign_irene_cif.y4m-%7B64,128,256,512%7Dk.h261>
>
>         The full integer range of bitrates from 1 to 512 can be found
>         here:
>
>         http://media.basilgohar.com/rtcweb/h261/
>
>         Target bitrate and actual bitrate start to match around
>         150kbps with
>         these new settings.
>
>         I am currently exploring other codecs with the same
>         methodology and will
>         share the results accordingly.
>
>         --
>         Libre Video
>         http://librevideo.org
>         _______________________________________________
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>
>
>
>
>
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