This post addresses the term bitrate, explaining how it relates to upload and download speeds and why it's important in live streaming. It's part of our series on HD live streaming.
Capturing live video with a high resolution and high frame rate does not guarantee your viewer will see that video in peak form.
To deliver high-quality live video to your viewers, you need to offer pipelines that can transfer your video data quickly and completely. Top-notch video requires a higher bitrate to look good.
What Is Video Bitrate?
Unsurprisingly, a video consumes a significant amount of data. The data stored in one minute of video is dozens of times bigger than a high-quality photo and hundreds of times bigger than an average email.
To deliver all of the information necessary to create a great video— live or otherwise— you need that data to transfer quickly.
Video bitrate is the amount of video data transferred in a certain period. Without a high bitrate, your high resolution and high frame rate video won't look as good as it could.
How is Video Bitrate Measured?
All digital information— including video— is made of bits.
We measure bitrates in bits-per-second (bps). Since the numbers are very large we usually talk about them in megabits-per-second (Mbps)— sets of millions of bits-per-second.
Note, the mark Mbps is different than MBps. Mbps stands for megabits-per-second. MBps stands for megabytes-per-second. We use Mbps for download and upload speeds and MBps to understand other things.
When does Bitrate Matter in Live Streaming?
In a live stream, there are two types of data transfers— uploads and downloads.
Uploading is the transfer of data from your local device to the internet. As a broadcaster, you take a video feed, send it to an encoder to compress the data as much as possible, and then transfer the video to the internet.
The other transfer type is downloading. Downloading occurs when your viewers receive the live video from the internet to their devices.
Bitrate is the way we measure the speed of the upload and download transfers. The faster the data transfers, the more overall data gets through. Higher quality video content requires more data, so a high bitrate allows you to stream at that level.
What Limits Video Bitrate?
For live streaming, video bitrate is limited by the amount of bandwidth you have for uploading and the capacity your viewers have for downloading.
Bandwidth is the maximum capacity of your network for uploading or downloading data— it's the pipeline for information transfers between the internet and your local network. Larger information requests require higher bandwidth to squeeze through. Smaller pipelines cause stoppages, slowing the transfer process.
We measure bandwidth— like speed— in Mbps. Your internet service provider (ISP) often advertises the bandwidth their network provides. Your ISP may offer 100 Mbps download and 5 Mbps upload, for example. The numbers are the cap on bitrates your network can handle.
In the 100-down, 5-up scenario, your capacity for downloading video content is relatively high, but if you're trying to broadcast, the 5 Mbps upload speed is limiting. While the minimum upload speed required for streaming 1080p30 video is 2.75 Mbps, we recommend a 13 Mbps bitrate to ensure a consistent top-quality broadcast.
How to Combat Limited Bandwidth
There are several ways to combat limited bitrate pipeline issues on both the broadcaster and viewer sides.
For upload bandwidth limits, high-efficiency video coding (HEVC or H.265) is a next-generation video codec that compresses up to twice as much video as its predecessor, advanced video coding (AVC or H.264). Without compromising quality, HEVC provides higher-quality streaming with the same bandwidth requirements of AVC.
For limits to downloading on the viewer side, broadcasters can stream over platforms that offer adaptive bitrate streaming (ABS). ABS offers buffer-less playback with automatic resolution optimization for the various viewer watching conditions.
Viewers with fast download speeds will receive the video in its full quality. Those with constrained bandwidth will receive lower resolution and lower frame rates to fit within their network limits.
Final Thoughts + Further Reading
The bitrate required for top-quality video is the main roadblock for streaming high resolution and high frame rate video. Network capacity is the main culprit.
It's always worth testing speed on your own to see if the bandwidth you're receiving matches what your ISP advertises.
At BoxCast, our BoxCast Platform and our BoxCaster and BoxCaster Pro encoders deliver adaptive bitrate streaming and efficient encoding to overcome some of the most significant issues.
Happy Streaming 😃!
