The data transfer rate, or the amount of the digital stream, or bitrate is a parameter that determines the amount of visual and audio information transmitted per unit of time. With the same type of compression, a higher bit rate will provide a higher signal quality. When using different compression schemes, the quality will be determined by both the bit rate and the compression efficiency. For example, the same bitrate in a MPEG-4 AVC signal provides better quality than an MPEG2 signal because AVC is more efficient.
There are two main approaches to the distribution of bits in a stream.
CBR (constant bitrate)
CBR shows a stable bitrate regardless of the scene and does not create sudden changes in load. Constant Bitrate is not optimal in terms of quality, because the stream does not change depending on the dynamics and complexity of the video.
- Ideal for data that is transmitted through limited media channels, as it allows you to use all the features of such channels.
- Affects the quality when encoding complex (highly dynamic) fragments that usually require more space.
- When encoding static video fragments, the consumption of allocated bits remains the same and the channel bandwidth is wasted.
- Sometimes with strict broadcasting to a narrow channel (CBR), bitrate walks up to 10% are allowed. Use programs to analyze encoded streams to check if the encoder is maintaining the correct bitrate.
Pros of CBR
- Can be used to transmit streaming media over a limited communication channel;
- The final document size can be predicted with high accuracy.
Cons of CBR
- Not suitable for works in which audio and video streams change dynamically, as it does not provide the optimal ratio of quality and size.
VBR (variable bitrate)
Allows you to increase the bitrate and reduce the compression ratio in difficult places to get a better image. Variable bitrate is adjusted depending on the rate of change of the picture. For example, the bitrate of a static video clip (sunset) will be significantly lower than the bitrate of motion (car chase).
- VBR reacts exclusively to the activity in the frame and allows you to significantly save space on your hard drive (when working with files).
- Allows for smaller encoded file size to provide much better image quality than CBR.
- Great for Internet Broadcasting (OTT).
- As the activity in the frame increases, the bitrate will also increase, so the system throughput can very quickly approach the limit value. As a result, there are a lot of artifacts and distortions in the final picture, up to its complete absence.
- Difficulty in foreseeing upcoming changes. The increase in bitrate during recording occurs with a delay.
Pros of VBR
- Files of different saturation can be encoded with a certain quality (much higher than when set to the average value);
- The size of the document is greatly reduced by fragments where a high stream width is not needed.
Cons of VBR
- It is impossible to predict the final size of the file – it can be much larger or smaller.
Average Bitrate (ABR)
ABR is a combination of the first two types! It is used when creating large projects. With a small file size, you can achieve the highest encoding quality, while the accuracy of the size calculation is much higher. The value in kbps is set by the user (as with CBR), and the program already varies it within certain limits (as with VBR).
Examining the existing types allows you to understand what the video and audio bitrate affects. The higher this indicator, the higher the quality of the finished multimedia product! This is the degree of compression – the more the signal is compressed, the worse the quality and the smaller the size. And vice versa!
- 32 kbps – For recording voice notes and for speech.
- 6 kbps – Suitable for low-quality speech or audio streaming.
- 128 or 160 kbps – Used in streaming.
- 192 kbps and 256 kbps – This is how audio files distributed on the Internet are encoded.
- 320 kbps – Maximum sound quality using the MP3 format.
- 400-1411 kbps – Used when creating HD audio in FLAC format (and analogs).
- 1411.2 kbps – Mainly used when recording uncompressed audio in LPCM format on audio CDs.
- 5644.8 kbps – Used when recording high-quality studio sound.
- 6,144 Mbps – Needed to burn DD+ audio to discs for Blu-ray players.
- 9.6 Mbps – Bitrate of multi-channel audio recorded on DVD-Audio discs.
- 18 Mbps is the value of stereo multi-channel audio using lossless compression.
- 400 kbps – Low-quality files taken on the camera of old phones.
- 750 kbps – Value used in YouTube 360p videos.
- 1 Mbps – Used for YouTube 480p video files.
- 2.5 Mbps – This YouTube bitrate is ideal for 720p videos.
- 3.8 Mbps – Can be used for YouTube videos at 720p at 60 fps.
- 4.5 Mbps is ideal for 1080p YouTube videos.
- 6.8 Mbps – YouTube video bitrate with 1080p and 60 fps.
- 9.8 Mbps – Used in DVD videos.
- 19 Mbps – Suitable for HDV standard with 720p and 1080p resolution.
- 24 Mbps – Video bitrate for video format recorded on AVCHD and Blu-ray discs.
- 25 Mbps – Used to record high-quality 1080i video.
- 29.4 Mbps – HD DVD video content.
- 40 Mbps – Used when recording Blu-Ray 1080p videos.
There is an average value that can be set almost always.
- For videos – 2.5 – 5 Mbps
- For audio files – 192 kbps
19 Mbps is suitable 19 Mbps.
2.5 – 5 Mbps is the best bitrate for streaming. You can broadcast with an image of 2560×1440 if you set a pass of 9000 kilobytes per second. In 4K mode, you need to set the bitrate for YouTube streaming to 20000 (20 megabytes per second).
The speed at which video is played during the stream. At the same time, the quality of the stream display depends on many parameters, including the characteristics of hardware and software. Knowing the bitrate allows you to determine the efficiency of data transfer and understand what the Internet speed should be for normal playback of the broadcast.