What is ABR Streaming:
Adaptive Bitrate Streaming is designed to deliver video in the most efficient way possible. It is able to switch between different qualities of the video to reduce buffering based on the users’ connection.
Example: When opening a video, it will start playing at the lowest quality. If your connection is fast enough, the video will switch to a better quality. It can also switch to lower quality in case your connection drops and then return to high quality once your connection is back to normal.
Apart from the resolution, the video also needs to have a bitrate setting. The bitrate is the number of bits that are transferred over a period of time, usually seconds. Whilst there isn’t one best bitrate for each resolution, here are the recommended settings:
- 1080p: 3500kbps to 4500kbps
- 720p: 2000kbps to 3500kbps
- 480p: 1000kbps to 2000kbps
- 360p: 400kbps to 1500kbps
- 240p: 300kbps to 700kbps
ABR vs. MBR
In defining ABR streaming, we should also explore what it’s not. Multi-bitrate streaming (MBR) sounds a lot like ABR in that it involves multiple available bitrates for playback devices to choose from. However, a playback device is locked in when it chooses one of these. In other words, it chooses what it thinks is best but can’t respond to sudden drops or increases in bandwidth. It turns out MBR lacks the “adaptive” part of ABR.
Also known as chunked encoding, or chunking, this is the process by which streaming data is separated into a series of non-overlapping segments before being sent to the playback device. Each chunk typically ranges in length from 2 to 10 seconds. By breaking up the data this way, it’s possible to adjust the size of data sent to a playback device mid-stream.
Now that the data is fully prepared, the viewer’s playback device takes the wheel. Before streaming begins, the playback device downloads a manifest that describes all the available chunks and bitrates. This is a menu from which the playback device can begin streaming. Typically, a playback device will take it slow, selecting a bitrate it knows it can handle before adjusting.
After each segment, the playback device recalibrates and requests the next segment based on the new information. For example, the first segment was likely a much lower bitrate than necessary. The device will then request a higher bitrate for the next segment. If the bandwidth lessens or the device otherwise struggles to play a segment, then it will adjust downward when requesting the next one.
Tips for choosing the right bitrate:
The used bitrate depends on the content of the video. For instance, if you are streaming a sports event like car races with a lot of movement, it is better to choose a higher bitrate, whereas a talk show with relatively static shots can use the lower end of the bitrates shown above.
Another factor is your internet connection. It is recommended that your bitrate doesn’t exceed 50% of your overall bandwidth. It would help if you also close other programs/applications that use up your bandwidth, especially when streaming from your own computer at home.