Bitrate is the number of bits per second a particular video file contains. Video bitrates are usually measured in megabytes per second (MBps), while megabits per second (Mbps) refers to transfer speeds. In general, the more bits or data a video contains, the higher its quality and the larger the file size will be. Bitrate is crucial for understanding whether broadcasters have enough upload bandwidth for video delivery and whether their audience has the bandwidth to download the stream.
There are multiple factors that impact video quality, however, such as its frame rate resolution and codec. For example, sports and other highly dynamic videos may require 60 frames per second (fps) for adequate quality rather than the standard 30 fps, which requires much more bandwidth. Many modern codecs can compress video more efficiently than in the past, which results in a higher quality video with a lower bitrate.
During the encoding process, most video encoders have different options for controlling the bitrate. Constant bitrate encoding (CBR) maintains a single target bitrate for the entire video file, which is useful to keep bandwidth requirements consistent during livestreaming. Variable bitrate encoding (VBR) adjusts the bitrate based on the complexity of each scene within the video. That means VBR can target a certain average bitrate, but use each bit more effectively to achieve slightly higher quality.
Considering which bitrates to stream video at is critical because viewers will have bandwidth limitations. For example, if the bitrate exceeds the user’s bandwidth, buffering or lagging can occur. Most video players attempt to keep a video buffer occupancy or amount of pre-downloaded video content to ensure smooth playback without interruptions, but higher bitrates could still overwhelm poor connections.
Since different bitrates require varying amounts of bandwidth during streaming, many broadcasters choose to offer multiple bitrates for their audiences. Many create an encoding ladder, which is a set of bitrates that’s optimized for a particular set of devices and networks. For example, Apple proposed a standardized fixed bitrate encoding ladder to help broadcasters improve video streaming. It’s also a good idea to offer one bitrate below 1000Kbps to ensure nearly anyone can view a particular video stream.
Modern streaming protocols like HTTP Livestreaming (HLS) and Dynamic Adaptive Streaming over HTTP (MPEG-DASH) also support Adaptive Bitrate Streaming (ABS). ABS can adjust streaming bitrates in real-time to handle fluctuations in bandwidth without leading to buffering. This ensures viewers are watching the best possible video quality that their current network and device can support.
Resi offers both hardware and software encoders for efficiently and reliably encoding and delivering video content to end-users. In general, Resi recommends users have an upload bandwidth at their broadcasting site that is 2.5x their target bitrate. This ensures there’s additional bandwidth available to handle packet loss and prevent buffering.
The Resi Livestream Platform also supports modern streaming protocols like HLS and MPEG-DASH that were designed for ABS. Combined with its cloud transcoding capabilities, Resi’s platform has everything broadcasters need to ensure efficient and resilient streaming with a wide range of bitrates.
