Live Streaming Data Rate and Usage

Streaming throughput for Live components

Calculating overall Live streaming usage

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:

Streaming throughput for Live components

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.

Technical Details: Target vs. Maximum - The Target rate shown below 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).

Capture component (quality)

Target rate (kbps)

Maximum rate (kbps)

Frames per second

Audio (medium)

32

32

--

Audio (high)

128

128

--

SD Video (480p)

Composite or DVI, all ratios

600

800

12.5 (PAL)

15 (NTSC)

HD Video (720p)

Composite (NTSC or PAL)

1062

1593

30 (NTSC)

25 (PAL)

HD Video (720p)

DVI 4:3

1770

2655

25

HD Video (720p)

DVI 16:9

2360

3540

25

HD Video (1080p)

DVI 4:3

3540

5310

15 (SCHD)

30 (PRO)

HD Video (1080p)

DVI 16:9

4720

7080

15 (SCHD)

30 (PRO)

 

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:

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:

 

Input Combinations

A/D

A/V

A/D/V

A/D/D

A/V/V

All SD

(DVI or composite)

728

728

1328

1328

1328

HD composite

(NTSC or PAL)

--

1190

--

--

2252

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.

Calculating overall Live streaming usage

There are two aspects of moving media from the classroom to students in real time:

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.

To calculate:

  1. The stream from the capture device to the Wowza server: 3550 kbps
  2. The stream from Wowza to 15 students: 15 x 3550 = 53,250 kbps or 53.25 Mbps
  3. 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.