When graphic designers start with motion graphics and video encoding, there is one huge misconception regarding file size and quality. Most graphic designers think video compression is like JPG compression. If you save your video in half of the size, the file size should be a quarter of the full size video. But that is wrong! If you want to understand video encoding the easy way, read on.
Another dimension to regard for video encoding
Most important fact to understand is that there is a new dimension in video: the time. As the unit for the quality of a video implies, time and data is the key to proper understanding of video encoding. The data rate of a video is measured in mbps, which stands for “mega bits per secondâ€. So a 4k video with 40mbps encoded is exactly the same size as the same video rendered with 40mbps and 2k frame size.
These two videos just differ in the visual quality as there is the same amount of data per second applied (data rate). As you might guess a 2k video fits 4 times in a 4k frame. So to achieve the same visual quality you should choose 4 times the bit rate for the 4k video. Or vice versa: One fourth of the data rate of a 4k video results in the same visual quality for a 2k video as its 4k equivalent.
The difference in TV and cinema frame sizes
There is a slight difference in the width of 16:9 cinema and TV format. So a 2k video (cinema) is slightly wider than a Full HD (TV) video. The 16:9 format frame size in TV is a multiple of 960px, the 16:9 format frame size in cinema is a multiple of 1024px. So a Full HD video frame size is 1920x1080px, a cinema 2k video frame size is 2048x1080px.
The following graphic depicts the most important frame sizes for TV and cinema frame sizes:
Most common video dimensions for cinema and TV
Keep this in mind when you encode your (self-hosted) video for a website
- Which data rate has the most common internet user for downloading available
- How many visitors do I expect to watch my video at the same time
- Is this video for mobile users preferably (who have lower bandwidth available)
A reference for video encoding
A video on YouTube is encoded with 5mbps for the video track and 128kbps for the audio track. Full HD and 2k videos are encoded with the H.264 codec, 4k videos with the Google/On2 VP9 codec, that produces a much better quality with the same data rate applied, but is way more computationally intensive than encoding with the H.264 codec. If you want to host the video on your website on your own webspace 5mbps is by far too much. For a self-hosted video on your website stick to Full HD or 2k video frame size and keep the video data rate between 1mbps and 2mbps with 128kbps audio. If you have fast moving subjects and lots of contrast choose higher data rates, if you do interviews with a static camera and solid background you can choose lower data rates. In the end it is a matter of trial and error to exactly know which data rate to choose. If in doubt do different renderings and choose the file that suits your needs regarding file size and quality.
Did this information help you to better understand how to apply data rate to you video output? If you have any more questions about video encoding write it in the comments below.
Add comment