Question / Help twitch reccomending Constant Bit Rate (CBR)

[retbergen]

http://blog.twitch.tv/2013/02/better-br ... -with-cbr/

To me it sounds wastefull on bandwith but I can get the point that routing mechanisms on the internet can be confused by a variable stream. Do you guys have any more insight or comments on this?

 

[dodgepong]

CBR results in more consistent bandwidth usage (fewer/smaller spikes), but consequently uses much more bandwidth and has very slightly less video quality. VBR has higher variations in bandwidth usage, but overall uses less bandwidth and has slightly better video quality.

Personally I still stick with VBR for a number of reasons:
* You can't use CBR and CFR together, and you have to use CFR to make sure your recordings can be opened in a video editor
* Most people can view my stream fine with VBR as far as I know
* I have transcoding options on my channel, so if my 720p+ is too choppy, viewers can reduce to 720p or lower, which is transcoded at CBR (alas, most streamers don't have this option)
* When I use CBR, my stream tends to get the effect of missing keyframes here and there, so the beginnings of VODs and when people first open the stream, it looks green and blotchy for several seconds before fixing itself. It just looks bad.

I might experiment with CBR more later, but I still haven't been convinced I need to change.

 

[shura30]

* Also, when I use CBR, my stream tends to get the effect of missing keyframes here and there, so the beginnings of VODs and when people first open the stream, it looks green and blotchy for several seconds before fixing itself. It just looks bad.

noticed this too switched back to vbr immediately

 

[XeiZ]

Dodgepong nails the cons of cbr except CBR and CFR, no you cant use them together like he said, but (using test11, no idea if thats important) i dont need CFR for CBR to open it in vegas (12) and have everything in sync.

 

[dodgepong]

Maybe the blotchiness is a problem with the way OBS does CBR? The Twitch transcodes don't have this problem, and they are CBR...

i dont need CFR for CBR to open it in vegas (12) and have everything in sync.

The problem I had before with not having CFR on is that I would get no video track at all when I tried to open it. I also wonder if the encoding was fast enough such that even with VFR, you were getting a constant frame rate because it was so solid? I dunno, just trying to think of things.

Honestly, the CFR thing is the biggest part that prevents me from using CBR. If my VODs could reliably be opened in an editor while using CBR (and I could figure out how to prevent the blotchiness from missing keyframes in VODs) then I would switch.

 

[XeiZ]

That makes me wondering....

This vod from yesterday was created due to a disconnect, so its starting up right in the action again and doesnt look blocky or "green" at all. First vod of that day neither.
1080p 30fps 3600cbr with ratetol of 5 , rc-lookahead of 60, aq-mode 2 and ref 4:
http://www.twitch.tv/xeiz/b/377074524

And my second test on youtube:
http://www.youtube.com/watch?v=ymuxAiJR_aI
Same settings but 720p and ref=9, opened a 5 hour CBR recording (no cfr obviously) in vegas and cut that part out.

Makes me think there is something different going on with CBR, maybe its extremly sensible about the connection to the streaming server?

 

[Lain]

The green thing is an bug with 0.472 that should be fixed in test revisions

 

[dodgepong]

The green thing is an bug with 0.472 that should be fixed in test revisions

oh neat u da best <3

 

[XeiZ]

Now that makes sense, i only recently started playing around with cbr and recordings....with test11... :p

 

[retbergen]

But does it makes sense? Why would twitch want this in the first place?

 

[dodgepong]

But does it makes sense? Why would twitch want this in the first place?

They explain it pretty clearly in the article.