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

[cowwoc <[e-mail]>]

Agreed. Both are usable, but 289 is tiring/annoying on the eyes.

Gili

On 05/12/2013 5:10 PM, Gunnar Hellstrom wrote:
> On 2013-12-05 22:24, Justin Uberti wrote:
>> oops - the h261-541kbps and h261-289kbps labels are swapped. Sorry 
>> about that...
> Ah, that explains my evaluation.
> So, 289 kbit/s is still usable for sign language. You can perceive the 
> important characteristics, but it is unpleasant and probably a bit tiring.
> And 541 good.
> So, if they were done at 25 fps then 541 is good and 289 usable.
>
> Gunnar
>>
>>
>> On Thu, Dec 5, 2013 at 1:21 PM, Justin Uberti <[e-mail] 
>> <mailto:[e-mail]>> 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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