Fast internet upload speed test - but slow Teradek encode rate???

[shanebankhead]

I have been trying to increase the video quality of our broadcasts with little success. When I run internet speed tests I consistently get 10Mbps or more upload. When I run the built in speed test on the Teradek it recommends 5Mbps encode setting. But when I run a broadcast through Meetinghouse Webcast it can’t seem to maintain more than about 500-800 Kbps regardless of the target encode rate.

I suspect it may be an issue with the ISP. But before I go down the long and arduous road of negotiating help from FM and the ISP, I just want to make sure I’m not doing anything wrong. Any suggestions?

[shanebankhead]

A few more details- I am setting the target bitrate to 2.5Mbps or 1.4Mbps. And have also tried using the “adaptive bitrate” option. I’ve tried setting bitrate options both on the Meetinghouse webcast side and directly in the Teradek console. Results are the same no matter what-it can’t seem to do much more than 5-800Kbps. Any ideas why this would differ so drastically from my speed tests?

[winjesluck]

Hi, Are you able to try using another camera?

I was going through the same thing last year and we ended up finding if we used a different camera it was alot clearer.

[russellhltn]

Have you tried the church's Region Latency (Ping) Test used to decide on which center you should use?

Edit: I'd also suggest testing different data centers. A low ping time doesn't always indicate that there's a lot of bandwidth to that location.

[shanebankhead]

@winjesluck Definitely not the camera, as that is what motivated this exercise. We just got upgraded to new HD camera and building system, and the video looks fantastic locally. So now we are wanting to translate some of this newfound video quality to our broadcasts.

@russellhltn Thanks for the suggestion about the Ping test. We did this a while ago, but I just checked again and there appears to be a newer server available now that has slightly better performance. Not nearly enough to explain the issue I'm having, but every little bit will help. We will try the new server on our next test.

So, still stumped... Performance does seem to fluctuate over time, so I'm still suspecting a flaky internet connection. Any other ideas are welcome.

[russellhltn]

Aside from the picture quality, where are you seeing the issue? I can't prove it, but I suspect the webcast system does something to conserve internet bandwidth. If possible, you might try 720. The webcast system may be downsizing if you exceed a certain resolution or bitrate.

[shanebankhead]

I think you're right about the webcast system doing some adjustments to conserve bandwidth. For instance, when I am broadcasting a black screen, the encode rate goes down to around 30Kbps, so there is definitely some content-related adjustment going on. However, in general, while broadcasting video, the quality seems to track the encode rate that I am reading from the webcast stats page. It reports the current/target encode rate there, so that's what I'm monitoring. When the encode rate gets below around 800Kbps, it starts to pixelate on movement. When it gets below 400Kbps we start getting glitches or dropouts.

It varies a lot over time, and often gets up to around 1.5Mbps, which I think corresponds to 720p-ish. But most of the time it seems to live in that 500-800Kbps range, which is about the "medium" encode rate for the webcast. This was fine with our older analog broadcasts. But now that we are doing everything in HD, and many more people are viewing at home, the expectations are suddenly higher.

Setting the Teradek to adaptive bitrate seems to help, as it will make adjustments on the fly, and we don't get as many dropouts, which makes sense. But still stumped why I can't get better performance on what "should" be a very fast internet connection.

[russellhltn]

For instance, when I am broadcasting a black screen, the encode rate goes down to around 30Kbps, so there is definitely some content-related adjustment going on.

That's to be expected. I think what the encoding does is send a full frame every so often, but sends "changes" from the prior frame for the in-between frames. If you have a static image, there will be no change, so the bit rate falls since there's no change to send.


You might want to try selecting a different data center. It's possible the connections from your ISP to them isn't sufficient. I'd also make sure the Teradek isn't overheating.

[CalS201]

You may have already worked through many of the things I will say, but others may also benefit from hearing this.

The first thing I would recommend is take the camera and Teradek to a location with a bright room and one that has a cable (not DSL) internet connection of at least 10mbps upload. Do a test using CBR (constant bitrate) at 2mbps. Test going to the church webcasting platform and also to Youtube. You may learn a lot from this exercise.
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Doing a speedtest closely simulates a webcast done with CBR-constant bitrate, where a constant stream of same sized chunks of data are sent to the destination. Speedtests do not simulate a webcast done with VBR-variable bitrate.
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Another factor is latency. If latency varies a lot, it can cause all sorts of problems with a video stream. The internet needs to be "consistent" in sending your stream of data. Go to the Azure website and test your latency to a specific datacenter. https://www.azurespeed.com/Azure/Latency
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If WIFI is on, you don't really know how much upload bandwidth you have dedicated to the Teradek - try turning it off and see if picture improves.
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Using variable, "adaptive" bitrate will try to maintain a certain picture "quality" at the expense of bandwith. Bitrate can and will vary below AND FAR ABOVE the target bitrate you set. This is a dangerous choice when you have limited bandwidth at the Chapel. Constant bitrate will provide a more reliable connection at the expense of picture quality (only during motion).
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Something that can affect the Teradek's ability to encode a picture efficiently is the amount of noise in the picture. If the lighting is on the low side (which is true in a lot of chapels) there will be a lot more noise in the many small blocks of the picture. The encoder will see this simply as a constantly changing block and "change" and will encode it for every single frame it sends out. The encoder will have to do this continually for each and every small block of noise. If you are transmitting VBR (variable) this will raise you overall transmitted bitrate and leave less bandwidth for the "real" parts of the picture - the worst part is when motion occurs - the encoder bitrate will rise to whatever it needs to encode the motion+noise. Consequently, it is more likely you will exceed the chapels available bandwidth. You don't EVER want to exceed the available bandwidth or even get close to it.

If you are transmitting CBR(constant) and you have noise, it will always leave less bandwidth for the "real" parts of the changing picture - but you never exceed the bitrate you set, and keep you within the chapels available bandwidth.
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You can minimize picture noise that the encoder has to process by setting the camera aperture wide open or increasing the light, then using a shutter speed to get the exposure right. At the same time, you must be aware that using a really slow shutter speed will also cause motion blur and the encoder will again have to work harder.
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Finally, be cautious about thinking the webcast statistics show you the real peak bitrates. It may be doing short term averages, or just reporting a snapshot bitrate periodically to you- neither of which is a true peak.

[russellhltn]

According to VidiU,

Adaptive Bitrate allows Vidiu to automatically adjust and stream at the highest quality achievable when bandwidth is limited

I interpret that to mean that it senses the available bandwidth and adjusts the quality accordingly.