What does bitrate mean, and how do I choose one?

Part 1. – Introduction to Bitrates

The term ‘bitrate’ refers to the amount of data that can be transferred per second (generally measured in kilobits). This has traditionally been the main way to control the quality of your stream, although there are other ways to increase the quality (for example: changing your framerate, source quality, etc.)

We have included below several commonly used bitrates, and what they are generally used to broadcast. However, there are other factors to consider when choosing your bitrate.

1.         For best performance the upload speed from your Encoder* should be at least 2.5x the bitrate you broadcast at.

Note: This is only a guideline, it is possible to broadcast at a bitrate closer to your maximum upload speed; however, doing so will greatly increase your buffering times and in-stream buffering.

2.         Consider the projected download speed of your target audience. A viewer should have 1.5x the download capacity of the bitrate they are watching at*. If your audience primarily has dial-up, broadcasting at a higher bitrate will be counter-productive.

Note: Again, this is only a guideline.

3.         Broadcasting at a higher bitrate leads to greater bandwidth consumption per user. This can lead to increased streaming cost. This may or may not be a concern for you.

*Below is a link to a popular speed test site which has test points located all over the globe.  All you will need to run this test is a java applet (which they will have you download if you don’t already have it installed).  It’s as easy as installing the applet then clicking the start test button.

Here is the link to the test site…

http://www.broadbandreports.com/speedtest?more=1

Simply select a test location nearest to you and then follow the directions.  The number that you will be interested in is the Kbps number, this will give you a basic idea of what your connection can handle.  The typical DSL connection has around 2044 kbps down and 768 up

Part 2. – Commonly used Bitrates (with examples)

Below is a list of common uses for internet broadcasts, with the appropriate bitrate to use for each. Simply find the description that best matches your needs to see examples of bitrates that may work well for you.

Note: Windows Media Encoder has many bitrate choices, the following bitrates are meant to act as guidelines only.

Audio

Voice only / AM radio

20kbps            - This is an excellent bitrate for broadcasts that are primarily talking. It can also be used for situations where bandwidth issues require a lower bitrate.

Music / FM radio

32kbps            - This is the current industry standard for FM radio broadcasts. IT will work well for any music broadcast, or as a higher quality option for voice broadcasts.

Music (higher quality)

64kbps            - Using this bitrate will provide a higher quality broadcast that works well for delivering near-CD quality music.

CD quality / MP3 quality

128kbps          - This is generally the highest audio bitrate you should use. It will deliver excellent quality. Note: You should compare a 64k broadcast to a 128k broadcast, as many people do not feel the slight increase in quality is worth doubling their bandwidth usage. This is a personal preference decision.

Below is a list of common uses for internet broadcasts, with the appropriate bitrate to use for each. Simply find the description that best matches your needs to see examples of bitrates that may work well for you.

Note: Windows Media Encoder has many bitrate choices, the following bitrates are meant to act as guidelines only.

Video

Static image (speaker at a podium)

128kbps          - This should generally be the lowest bitrate that is used for video. It can be used in situations where there will not be significant movement, or in situations where bandwidth or budgetary issues require a low bitrate stream.

Multi-use Video broadcast (conferences, special events, sporting events, concerts, etc)

282kbps          - This bitrate is the current internet standard for video broadcasting. Most viewers on a DSL, cable, or other high-speed connection can effectively view these broadcasts. It is generally effective for all video broadcasts (except in cases where a higher level of detail is required), although you may still wish to use a higher bitrate.

High quality Video broadcast (weddings, sporting events, racing, etc)

548kbps          - This bitrate will provide a higher quality broadcast that is often preferred by people whose broadcasts contain a lot of movement or action. It is also an alternative to 282k broadcasting if you want a higher quality. Note: Some viewers may have difficulty watching your stream.

Fast action video, High detail video, Very high quality broadcasting

1128kbps        - This is used for delivery of very high quality video broadcasts. Your viewers should be on a cable connection or better. This level of broadcast is necessary for quality broadcasting of fast moving events (sailing, car racing), and can also be very effective for situations that require a high level of detail. Often broadcasters will offer this in addition to a lower quality broadcast. The picture and sound quality is very good.

DVD Quality video

2137kbps        - A very high level stream that would be most effective for a specific audience, as many viewers may not be able to view it.

Part 3. – Framerate

The framerate of your video broadcast determines how many ‘frames’, or new images, are shown per second. A video stream with a high bitrate and a low framerate will have a very clear image, but you may see an increase in the choppiness of the broadcast. A video with a high framerate and a low bitrate will have a ‘fuzzy’ image but show movement smoothly.

Standard framerates:

15fps - Internet broadcast

24fps - Film

29.97fps - Internet broadcast

30fps - TV / DVD

59.94fps - DVD

Using Windows Media Encoder you can select any framerate you wish. However it is important to know when to change the default settings. This is generally determined by the type of content you are going to broadcast.

Scenarios

Fast action video
-Sporting events, Racing, etc.

When broadcasting a video stream that has a lot of movement, especially fast movement, it is important to have a higher framerate. This will keep your broadcast looking smooth, and avoid having blurs or ‘trailing’ effects. Deciding whether or not to go with a higher or lower bitrate (which affects the clearness and detail), however, depends on what you are broadcasting.

Low movement video
-Church services, Instructional videos, etc.

When broadcasting a video stream that has limited or slower movement you can lower the framerate without sacrificing the quality of the broadcast. A 10fps or 15fps framerate will still allow you to broadcast a clear stream. Again, deciding whether or not to go wit ha higher or lower bitrate depends on what you are broadcasting.