[rtcweb] H.261 performance (Re: Stephan Wenger's choices)

Harald Alvestrand <harald@alvestrand.no> Mon, 30 December 2013 09:59 UTC

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Date: Mon, 30 Dec 2013 11:00:10 +0100
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Subject: [rtcweb] H.261 performance (Re: Stephan Wenger's choices)
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On 12/28/2013 10:50 PM, Gunnar Hellstrom wrote:
> On 2013-12-28 22:24, Ron wrote:
>> On Sat, Dec 28, 2013 at 11:20:28AM -0800, Eric Rescorla wrote:
>>> Even if we mandate H.261, there is a reasonable chance of their
>>> expectations being thwarted, since they might well expect that
>>> the quality of video would be comparable, yet it will not.
>> You don't get much more thwarted than "no video for you", the only
>> direction from there is up.  Given a device with a ~4 inch screen,
>> viewed from a foot or two away, possibly in open daylight, maybe
>> even while bouncing around on a bus or train or while walking,
>> maybe with a bunch of scratches on the screen or a plastic cover,
>> there's a fair bet that a significant percentage of viewers wouldn't
>> be able to pick the difference between it and a perfectly lossless
>> image stream anyway.
>>
>> Is it going to be worse than NTSC television?  How many people were
>> happy enough to keep buying and watching those?  How many still
>> would if it was all that they could get?
> H.261 has only CIF and QCIF formats defined. Modern cameras tend to 
> not support these formats anymore, more often delivering formats like 
> QVGA , VGA and various wide screen formats. And applications adapt to 
> these modern cameras.
> Using H.261 sometimes and modern codec sometimes will create 
> situations when you will get unpleasant compromises in video formats, 
> such as cropped pictures, or pictures with unused margins, or 
> processing-costly remapping that also reduces quality.
>
> That together with the low quality makes it not desirable.

FWIW, my experiments with FFMPEG's H.261 encoder seem to indicate that 
rescaling a HD picture to CIF and encoding with H.261 is quite a bit 
faster than encoding the picture in HD with VP8 or H.264.

H.261 has quality issues, but I don't think it has speed issues, even if 
you add a remapping stage.