How does doozzoo handle bandwidth fluctuations?

Modified on Wed, 26 Oct, 2022 at 12:39 PM

Video quality dynamically adjusts based on the strength of a user's network connectivity. This is done by the Subscriber (student) sending feedback packets to the publisher (coach) that say "My network quality is at 'x' level. Please adjust your published video bit-rate to accommodate my current bandwidth". The faster and more stable a Subscriber's broadband connection is, the better the video quality it will request.

This mechanism works well until a certain point. If a Subscriber's bandwidth drops below a certain threshold, or if a Publisher has very little bandwidth to upload video, behavior can be unpredictable. Video may be choppy, audio may have artifacts, and the connection could be dropped.

We recommend a minimum dedicated 350kb/s down per downloaded stream, as well as 350kb/s up per uploaded stream to maintain a stable video connection.

For various resolutions and quality combinations, the bandwidth requirements are outlined below.

Excellent - None or imperceptible impairments in media
Acceptable - Some impairments in media, leading to some momentary disruptions

Audio + Video Streams

For the given qualities and resolutions, all the following conditions must met.

Quality	Video Resolution @ FPS	Video kbps	Packet Loss
Excellent	1280x720 @ 30	> 1000	< 0.5%
Excellent	640x480 @ 30	> 600	< 0.5%
Excellent	352x288 @ 30	> 300	< 0.5%
Excellent	320x240 @ 30	>300	< 0.5%
Acceptable	1280x720 @ 30	> 350	< 3%
Acceptable	640x480 @ 30	> 250	< 3%
Acceptable	352x288 @ 30	> 150	< 3%
Acceptable	320x240 @ 30	> 150	< 3%

Note that the default publish settings for video are 640x480 pixels @ 30 fps in OpenTok.js and the OpenTok iOS SDK. The default is 352x288 @ 30 fps in the OpenTok Android SDK.

Audio-only Streams

For the given qualities, the following conditions must met.

Quality	Audio kbps	Packet Loss
Excellent	> 30	< 0.5%
Acceptable	> 25	< 5%