Understanding Bitrate
Bitrate is a metric that indicates the speed at which digital data is transmitted. It’s expressed in bps (bits per second), representing how many bits are transferred in one second.
Bit and Byte are units of digital data, with bits denoted as ‘b’ and bytes as ‘B’. One byte consists of 8 bits. For instance, if a file size is 8MB (Megabytes), it is equivalent to 64Mb (Megabits).
Bitrate of Audio
The bitrate of an audio file indicates how much audio data is transmitted over a specific duration. For instance, a 16-bit 44.1KHz audio file means that there are 16 bits of data 44,100 times in one second. The transmission rate differs between Mono and Stereo, with Stereo having twice the rate of Mono.
Bitrate Examples
Mono 16-bit 44.1KHz: 16 x 44,100 = 705,600 bits per second.
Stereo 16-bit 44.1KHz: 16 x 44,100 x 2 = 1,411,200 bits per second.
Bitrate is one of the primary indicators of data transfer rates. It’s usually expressed in bps (bits per second) and represents the transmission rate.
A 192Kbps MP3 file means a data transfer rate of 192,000 bits per second, which has about 1/10 of the compression loss rate compared to a PCM wave file (1411Kbps).
It’s crucial to note that there’s often confusion between bitrate (Kbps) and sampling rate (KHz) when used in many contexts.
Calculating Audio File Size
Let’s take an example where the audio is recorded at a bitrate of 320Kbps.
Calculating the size of audio for 1 second
320Kbps translates to 320,000 bits per second. To convert this value to bytes, divide by 8 (since 1 byte = 8 bits). 320,000 bits ÷ 8 = 40,000 bytes = 40KB
Thus, audio recorded at a bitrate of 320Kbps has a size of approximately 40KB for 1 second.
Calculating the size of audio for 1 minute
Given that 1 minute contains 60 seconds, 40KB/s × 60 seconds = 2,400KB = 2.4MB
Therefore, the audio for 1 minute is approximately 2.4MB in size.
Calculating the size of audio for 1 hour
As 1 hour comprises 60 minutes, 2.4MB/m × 60 minutes = 144MB
By this calculation, the audio for 1 hour has a size of approximately 144MB.
Bitrate of Video
Similarly, the bitrate of a video is also a crucial determinant of its quality and size.
For videos, due to the need to handle more complex visual data, such bitrates can be measured in larger units like Mbps (megabits per second). The bitrate of a video is dictated by various factors such as its resolution, frame rate, and color depth.
Let’s delve deeper into the bitrate of video.
Resolution and Pixels
The bitrate of a video is determined by its resolution and frame rate. A 1080p resolution comprises 1920×1080 pixels, and each pixel holds RGB color information. Given that RGB is made up of 8 bits of data for each color, a single pixel requires 24 bits of data.
Consequently, the entire capacity for one frame is 1920 x 1080 x 24 bits.
Bitrate Calculation for Frames
For a 1080p video, one frame requires roughly 50Mbit of data. So, for a video at 24 frames per second, the data required for one second would be around 1200Mbps.
Video Compression
A pure 8bit color format 1080p video at 24fps, when uncompressed, has a bitrate of 1,200Mbps. However, most modern video devices or mirrorless cameras compress videos to optimize storage space and transmission speed. For instance, if a 1080p 24fps video is stored at 50Mbps or 25Mbps, this indicates a substantial compression rate compared to the original data.
Compression rate is a pivotal factor determining the quality and file size of a video. A high compression rate reduces the file size but may also degrade the video quality. XAVC is one of the video codecs developed by Sony, offering both efficient compression rates and high quality simultaneously.
Calculating Video File Size
The size of a video file can be estimated based on the bitrate of its codec.
For instance, let’s assume a video is shot at a bitrate of 100Mbps.
Calculating the size of video for 1 second
A bitrate of 100Mbps translates to 100,000,000 bits of data per second. To convert this value to bytes, we divide by 8 (since 1 byte = 8 bits). Thus, 100,000,000 bits ÷ 8 = 12,500,000 bytes or 12.5MB.
Therefore, a video shot at 100Mbps will have an approximate size of 12.5MB for every second.
Calculating the size of video for 1 minute
Given that there are 60 seconds in a minute, 12.5MB/s × 60 seconds = 750MB.
This means, a one-minute video will be roughly 750MB in size.
Calculating the size of video for 1 hour
As there are 60 minutes in an hour, 750MB/min × 60 minutes = 45,000MB or 45GB.
By this calculation, a one-hour video will have an approximate size of 45GB.
It’s worth noting that this calculation represents the size of uncompressed video data. In reality, videos are compressed through codecs, so they might have a much smaller bitrate than the theoretical calculation suggests.