Webcast upload bandwidth requirements

Conversations around originating a webcast for conference, including cameras and mixers.
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Webcast upload bandwidth requirements

Postby CalS201 » Sun Jun 01, 2014 8:13 pm

Over the last couple of years, we have originated stake conference webcasts from 3 of our 4 bldgs with good success. We avoid the 4th bldg because the U-Verse internet connection is only 6mbps down/.94mbps up rate (measured on several occasions). Recently we did a 1.5hr test webcast from the 4th bldg using the "High 4x3 (recommended bandwidth 1.7M up, 1.3M down)" Preset found in the webcast pgm. The webcast was received (in the same bldg) at 896kbps with no dropped frames or apparent problems for 1.5hrs.

This leads me to ask: Why is it recommended to have 2X the required upload bandwidth? Isn't the buffering that occurs on the headquarters server supposed to makeup for occasional uplink connection rate slowdowns? What would happen to the picture or sound if the upload rate occasionally dropped below 1X ? I am especially interested in hearing from anyone that might understand the technical aspects involved.

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Re: Webcast upload bandwidth requirements

Postby rannthal » Mon Jun 09, 2014 2:18 pm

I wouldn’t trust those preset settings. They are obviously wrong. Where in the world would you ever find bandwidth speed that has a higher upload then download. Also if you look closely, you’ll notice that the High 16x9 has the same speeds as the High 4x3. This also isn’t correct, the 16x9 needs a higher speed then the 4x3 to produce the higher picture quality. So if you are using a preset, I’m not sure at what the speeds actually are, they obviously aren’t what they say they are.

The reason for the 2x required upload speed is to give that buffer so if the bandwidth drops, it won’t go below the required speed. The headquarters servers take what they are given and then transcode it to the receiving sites. When the bandwidth speed drops below the encoding speed, the encoder tries to encode with the speed that it has, but doesn’t have enough speed to get everything that it needs. This causes the picture quality to degrade, pixelate, freeze, etc. and if bad enough possibly have sound loss. The receiving end would receive the same picture quality that is being sent by the encoder.

To understand what it is like to over encode, try customizing the speeds to where you know the encoder is expecting a faster speed then you actually have. Then try receiving the stream that is produced and see what it is like.

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Re: Webcast upload bandwidth requirements

Postby jonesrk » Wed Jun 11, 2014 1:22 pm

I think that the upload speed requirement is for the originating site, while the download requirement is for the receiving sites.
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