Live streaming is the real time streaming of media from a classroom device to a media server, then providing that streamed media to students and instructors. Unlike on-demand playback where the video can be buffered over time and can cope with large fluctuations in available bandwidth, live streaming is much more sensitive to network quality and available bandwidth. As such the requirements for a good student experience are higher than for on-demand material.
The key components that will determine the demands placed on your network for live-streaming are:
- How many students will be viewing the live-stream from ON-CAMPUS?
This number may be very small, limiting YOUR bandwidth requirement to provide the stream. Institutions may only provide live-streamed classes for distance-education sections. Remote users who are off campus are not using the institution's network and do not need to be figured into the bandwidth requirements.
- What types of connections are being used for the visual inputs?
Live stream bandwidth figures are specified as a maximum bandwidth requirement. Unlike on-demand where the player can significantly buffer the recording, the opportunity for buffering a live stream is limited. As such, all calculations need to be done on a worst-case basis. While the actual average bandwidth usage may be significantly lower, there will be periods during the stream where complex images or fast movement or low lighting will cause the data-rate to burst higher. If there is not sufficient bandwidth for these events the playback experience will suffer.
DVI connections allow for higher resolution inputs, but require higher volumes of data than Composite (analog) connections do. Composite connections can only be video, but DVI connections can return either a display or a video camera feed. Meaning, if your live-stream includes two high-definition digital video cameras, connected to the capture device via DVI, the amount of data being streamed back to the users is going to be significantly higher than 2 composite inputs. This is covered in more detail below.
The following table lists the target and maximum data rates for each possible component of live streamed media. This is the base information used to determine the combined data rates for each type of Live stream possible.
|Capture component (quality)||Target rate (kbps)||Maximum rate (kbps)||Frames per second|
|SD Video (480p)
Composite or DVI, all ratios
|HD Video (720p)
Composite (NTSC or PAL)
|HD Video (720p)
|HD Video (720p)
|HD Video (1080p)
|HD Video (1080p)
Technical Details: Target vs. Maximum - The Target rate shown above is representative of the average bitrate used for each component. In a situation where the feed is more challenging (high-motion, low-light) the bitrate will be closer to the Maximum value.
Static display content (e.g., a presentation where pages are changed infrequently) requires a lower bitrate than dynamic content (e.g., a monitor showing a full motion video throughout).
These are the base numbers we use to provide the combined component calculations shown below. Now…just so you understand how we got to the combined figures, be sure you understand the following:
- A composite connection can only be to a video camera. The bitrate is determined by the quality setting (HD or SD) but because it’s analog, no other values apply.
- A DVI connection can capture from a display device OR from a video camera. And because it’s a digital connection both the quality setting (HD or SD) and the ratio configured (4:3 or 16:9) affect the bitrate of the data stream.
- All sources will be captured at the same quality. All visual aspects are streamed/captured in SD or HD as selected in the capture configuration. It is not possible to capture one input at HD and the other at SD.
As is indicated earlier, what this means is that determining the needed streaming rates has less to do with what combination you are streaming (AV, ADV, AVV) and MORE to do with the type of connection you are using, along with the quality and ratio you have set for the inputs being captured.
The below table provides combined calculated data stream rates for all of the possible combinations (except audio only). We do this for you, so you don’t have to. You’re welcome.
Please note the following about the below calculations:
- The figures shown are in kbps (kilobits per second).
- The calculations use the high-quality Audio bit rate and the Target bitrate for the other input types from the table above.
- The DVI calculations apply to both 4:3 and 16:9 ratios - the higher (16:9) bitrate figure is shown below.
(DVI or composite)
(NTSC or PAL)
|All HD DVI||2488||2488||4848||4848||4848|
|HD composite + HD DVI||--||--||3550||--||3550|
Notice in the above table that the bit rates for each input combination are the same across all of the multiple-visual-input streams, regardless of whether it’s dual video, dual display, or video/display. That’s because the connection and ratio determine the bitrate, not necessarily the thing being streamed. But as also stated above, static content uses less bandwidth than non-static or high-motion content.
There are two aspects of moving media from the classroom to students in real time:
- The throughput of the media from the capture device to the live-streaming media server (in this case a Wowza server).
- The subsequent throughput of the streamed media from the server to each student tuned into the Live class.
To calculate the total data streaming rate for a single live class, take the data rate for the media combination you are streaming (from the above table) and multiply it by the number of students watching the live class ON CAMPUS. You don’t have to worry about students watching from somewhere else. They're not bogging down your network.
Be sure to add one extra streaming instance to account for the data being streamed from the device to the streaming media server.
For this calculation, we are using the following assumptions. Substitute your own situational data to generate your own calculations.
- The Live class will be streaming Audio, Display (DVI), and Video (Composite).
- The section has 100 students in it, but you expect only 15 students to view the class from on-campus.
- The quality selected for the capture is High Definition (applies to both video and display).
- These selections result in a target data rate for this A/D/V stream of 3550 kbps (from the above table).
- The stream from the capture device to the Wowza server: 3550 kbps
- The stream from Wowza to 15 students: 15 x 3550 = 53,250 kbps or 53.25 Mbps
- Add them together to get the bandwidth needed for all: 53,250 + 3550 = 56,800 or 56.8 Mbps
So to be clear, that's a total on-campus data streaming rate of 56.8 Mbps for this Live class, provided 15 students watch the class live, individually, from ON-campus. Your calculations may end up being lower if, for example, you only stream Live classes for sections with students who are NOT on campus.
Alternately, you may only use live streaming for popular speakers where you believe a large percentage of on-campus users will be viewing the stream and not using up your bandwidth with something else. For these situations, you can reduce the number of individual streams by providing the live-stream in a location where a large number of users can watch it together.
You will want to check the maximum bandwidth capability for your network, or check with your network vendor, to determine the maximum bandwidth of your wireless and wired connections. Use this information to determine the optimal configuration for live streams (what inputs to use), and which sections need to be streamed live (only those where most/all students will view from off-campus). You may also recommend that students watch the stream via a wired connection instead of a wireless connection.