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

[Gunnar Hellstrom <[e-mail]>]

On 2013-12-05 23:31, cowwoc wrote:
> Agreed. Both are usable, but 289 is tiring/annoying on the eyes.
That makes the old experience very likely still true: around 360 kbit/s 
is needed for good usability and then CIF and 25 (or 30) fps should be used.

How about robustness against packet loss and jitter?

Well there are at least a couple of methods to indicate packet loss and 
need for refresh mentioned in RFC 4587.

Gunnar
>
> 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
>>>             _______________________________________________
>>>             rtcweb mailing list
>>>             [e-mail] <mailto:[e-mail]>
>>>             https://www.ietf.org/mailman/listinfo/rtcweb
>>>
>>>
>>>
>>>
>>>
>>>
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>>
>>
>>
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