VP8 suitable for screen sharing?

[pablo platt]

Hi

In a screenhero talk they claim that VP8 is not ideal for screen sharing.

From my experience there are quality issues in screen sharing and I'm not sure if it's because of my setup.

Discussion starts at 02:40

http://blog.screenhero.com/post/75735042883/behind-the-scenes-a-peek-at-screenheros-real-time

Is my understanding and the analysis in the video correct?

Thanks

[Philippe Clavel]

Hi Pablo,

For screensharing the codec matters, but you can get good result on VP8 assuming you control the encoder and the encoding parameters.

We have done it in both H264 and vp8 and both worked fine.

Thanks,

Philippe

[Justin Uberti]

The video isn't accurate on a number of technical grounds, primarily regarding the fact that what they call "vp8" is really "webrtc's usage of vp8". 

There, the main issue is that webrtc is trying to maintain high image quality for screenshare, and not maintain high fps. You can see this in the max quantization that is chosen for screenshare. Clearly, when favoring image quality, you are going to get frame drops when the bandwidth is insufficient.

This video was shot back in February, and there have been a number of improvements to screenshare since then. Some of the criticisms are valid based on the state of things back in February, but have now been addressed.

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[pablo platt]

I'll try screen sharing again and see if the quality improved.

Thanks

[Justin Uberti]

Try Chrome 37 for the latest and greatest.

[Piyush Ranjan]

Would vp9 be better ? When would VP9 be added to webrtc ? If I am not mistaken, VP9 is already added to both chrome and FF.

[Justin Uberti]

VP9 has a lossless mode which will be great for screensharing, but it is still early days for VP9. Expect to see it working well in Chrome later this year.

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[Faraz Khan]

Pablo,
I'm actually one of the guys in that video (and a co-founder at Screenhero) and I agree that we did get a bit carried away and I apologize to everyone at webrtc for that! - we will definitely be more considerate in the future. We actually didnt know that the video would be put up on the internet and we were just trying to add humor to the presentation! We love webrtc (the screenhero networking/rtp/audio stack is almost 100% webrtc) and it would have not been possible to get a solution like this up so quickly without the great work they have done.

The problem with VP8 we were trying to highlight was that of bitrate adherence. We also used libvpx directly (not through webrtc). Using libvpx directly we were able to get much better control / results but there was still one big issue. There is no per-frame VBV support in VP8 which means that though bitrate would be respected on average over a second, it may not be respected for time samples of  1 / framerate (s). This would happen even if you set the max quantizer to 63.

As Justin suggested, this may have changed since Jun 2013 but was a issue till then. Thats when we officially switched from vp8 to x264 for our screen sharing.

Again - this may not be an issue for you. A large spike in frame size would cause the decoder on the remote side to lag - and most screensharing solutions seem to be okay with lag. We wanted to build a solution where lag was eliminated (as much as physically possible) and the effects of your remote inputs provide instant feedback.

What problems are you experiencing with the screenshare?

[Piyush Ranjan]

Hi Phillippe

Can you please throw more light on which parameters you changed in VP8 ?

Piyush

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