Re: [rtcweb] H261/MPEG-1 video quality

Maik Merten <maikmerten@googlemail.com> Thu, 14 November 2013 19:54 UTC

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Date: Thu, 14 Nov 2013 20:54:15 +0100
From: Maik Merten <maikmerten@googlemail.com>
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Subject: Re: [rtcweb] H261/MPEG-1 video quality
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I included the JavaScript MPEG decoder so that people can have a quick 
look. I don't propose that videos should be decoded in JavaScript for 
WebRTC. If anything this merely demonstrates that old codecs have low 
processing requirements (duh!).

Maik

Am 14.11.2013 20:48, schrieb Gili:
>
> Just a reminder: Native applications don't necessarily have access to
> Javascript (they're running outside of a browser) so a Javascript-based
> solution sounds problematic to me. Everything we need should be
> accessible from WebRTC's Native API. If that happens to include a
> Javascript engine under the hood, so be it, but I just want to make sure
> this is understood.
>
> Thanks,
> Gili
>
> On 14/11/2013 2:35 PM, Leon Geyser wrote:
>> >>This includes a completely JavaScript-based MPEG-1 player for those
>> that don't happen to have a fitting decoder installed >>(also, yay,
>> JavaScript is fast enough now for simple video decoders!). I recreated
>> the encoded files to ensure there are no >>b-frames and documented the
>> encoder settings accordingly.
>> Thanks for sharing. Looks better than what I expected.
>>
>> On 14 November 2013 21:12, Maik Merten <maikmerten@googlemail.com
>> <mailto:maikmerten@googlemail.com>> wrote:
>>
>>     Hello again,
>>
>>     to allow for having a quick look at some test sequences I put
>>     together a very very sloppy overview page at
>>
>>     https://dl.dropboxusercontent.com/u/14053306/mpeg1/index.html
>>
>>
>>     This includes a completely JavaScript-based MPEG-1 player for
>>     those that don't happen to have a fitting decoder installed (also,
>>     yay, JavaScript is fast enough now for simple video decoders!). I
>>     recreated the encoded files to ensure there are no b-frames and
>>     documented the encoder settings accordingly.
>>
>>     Best regards,
>>
>>     Maik
>>
>>
>>     Am 14.11.2013 11:52, schrieb Maik Merten:
>>
>>         Hello all,
>>
>>         in
>>         http://www.ietf.org/mail-archive/web/rtcweb/current/msg09721.html
>>         a
>>         sample of H.261 video was provided, connected to a (rhetorical?)
>>         question if this provided quality would be acceptable for
>>         users. Clearly
>>         that provided sample is of very low and unacceptable quality.
>>
>>         Just for comparison, here are two CIF samples at roughly 256k
>>         created by
>>         a somewhat modern encoder (ffmpeg with rate/distortion
>>         optimization):
>>
>>
>>         https://dl.dropboxusercontent.com/u/14053306/mpeg1/irene-256k.mpg
>>
>>         https://dl.dropboxusercontent.com/u/14053306/mpeg1/mad900-256k.mpg
>>
>>
>>         (encoded as MPEG-1 video, as the "h261" encoder in ffmpeg
>>         crashes when
>>         using rate/distortion optimization. I understand MPEG-1 if
>>         used without
>>         b-frames is similar to H.261 in coding efficiency, but mostly
>>         adds more
>>         flexibility regarding frame sizes.
>>
>>         ffmpeg -i sign_irene_cif.y4m -vcodec mpeg1video -mbd rd
>>         -trellis 2 -cmp
>>         2 -subcmp 2 -g 100  -vb 256k irene-256k.mpg )
>>
>>         Even without formal testing it is obvious that H.261 and/or
>>         MPEG-1 video
>>         is clearly outperformed in terms of coding efficiency by H.264
>>         and VP8.
>>         However, personally, speaking as an end-user, I would very
>>         much prefer
>>         this video quality over audio-only calls (in cases where
>>         transcoding is
>>         not available), as the video produced still carries useful
>>         information.
>>         Also H.261/MPEG-1 is blazingly fast, can be dealt with in
>>         software, and
>>         is not exceedingly difficult to implement.
>>
>>         Of course a MTI codec with higher coding performance is much
>>         preferable.
>>         However, if no such high-performance codec with licensing
>>         terms that are
>>         acceptable for all communities can be agreed on I think it may
>>         be wise
>>         to seriously evaluate the option of implementing an outdated
>>         codec for
>>         the sake of interoperability. In practice, most calls will
>>         negotiate to
>>         H.264 and VP8 anyways, but sporadic negotiation failures that are
>>         difficult to account for by the user are still to be expected
>>         if no MTI
>>         codec is defined at all.
>>
>>
>>
>>         Best regards,
>>
>>         Maik
>>
>>
>>     _______________________________________________
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>>     https://www.ietf.org/mailman/listinfo/rtcweb
>>
>>
>>
>>
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