What is video compression?
Video compression is the process of reducing video file size while still retaining the necessary video data. You do this using codec software, which decides what information is required for the video to retain its quality and what information can be discarded. There are a few different video codecs, all of which are responsible for compressing (and decompressing) the video in unique ways.
What makes video files so big?
The algorithms behind video compression may be complex but it’s not hard to understand what makes a video file larger or smaller. There are three primary factors that dictate video file sizes: the resolution, the bitrate, and the encoding. Knowing these will help you to slim those file sizes down without turning your video blocky, or muddy, or petulant and self-absorbed.
Resolution is the actual size, in pixels, of your video image. When people refer to a video in terms of “1920 by 1080” or “4K,” they are referring to the video’s resolution. 1080p high-definition video, for example, has an image size that is 1,920 pixels wide and 1,080 pixels tall. That’s over 2 million pixels per frame of video, with each pixel holding unique data identifying the color and brightness. Multiply that by the number of frames per second, commonly between 24 and 60 frames per second, and you can start to see why uncompressed video files are so large.
Bitrate relates to the amount of data being transferred at a given time. This is typically measured in bits per second (bps), kilobits per second (Kbps), or megabits per second (Mbps). In terms of video bitrate, a higher bitrate means a larger amount of video data can be transferred per second. Higher bitrates produce higher video quality but also make for larger file sizes. Lower bitrate means less data is transferred and, thus, smaller file sizes.
It’s also possible to encode a video using Constant Bitrate or Variable Bitrate. Constant Bitrate maintains a consistent rate for the duration of the video. Variable Bitrate, however, will adjust the rate depending on the complexity of the video from moment to moment. Variable Bitrate is, essentially, a form of video compression itself that results in smaller file sizes than Constant Bitrate.
Video encoding is the process of applying compression and rendering out or converting a video file from one file format to another. There are two key elements of a video file during the encoding process: the container and the video codec.
- Container. The container is often what people are referring to when they say the “file format”. Common examples of a container would be MP4 and MOV files types.
- Video codec. The codec is held within the container and is responsible for applying the compression. Different codecs handle compression in different ways. Think of it as using different mathematical methods to solve the same problem.
7 easy ways to reduce a video’s file size
Create a ZIP file
If you need to reduce the file size of a video to email or upload it to someone, creating a ZIP archive may be the best choice. Best of all, you don’t lose video quality when creating a ZIP file.
Think of a zip archive like a folder. The archive can hold many files and even other folders full of files. When you zip an archive, all the files and folders within are compressed to a smaller size without any loss of data. However, the zip archive itself appears as a single file so in order to access the file the archive needs to be unzipped, restoring all the files contained to their original size. This is why this is great for transferring files but won’t work for uploading to video sites.
The ability to zip and unzip archive files is built into both Windows and iOS.
- On Windows right-click on the file or folder you wish to zip. Select Send To and then select Compressed (zipped) folder.
- On iOS Control-click on the file or folder. Choose Compress from the shortcut menu.
Keep in mind that you can’t upload zip files to YouTube or social media sites, so this method will not work when you need to post a video online.
Reduce the length of the video.
Another option to reduce the file size on your video might be to shorten the video itself. Is there extra time at the beginning or end of the video? Perhaps sections in the middle that are unnecessary? Shortening the overall runtime of the video by trimming out these unneeded parts will result in a smaller video file.
This can be accomplished with any video editing software. The workflow will be similar for most applications such as iMovie, Adobe Premiere, or using Descript’s video editor.
Here’s how to reduce the length of your video using most video editing software:
- Import the video file to your video editing software.
- Add the video to the timeline.
- Use the slice, cut, or trim tool to shorten the beginning and end or remove any portions you wish.
- Select Export, share, or render depending on the software you are using. This would be a good time to incorporate the next few suggestions as you set the encoder options to further reduce file size.
Reduce the resolution of the video.
Consider where the video will be viewed. If you intend to upload the video to YouTube and the original file’s resolution is larger than 1080p, you could reduce file size greatly by lowering the resolution to 1920 pixels by 1080 pixels.
However, if you are uploading a video to social media or a platform where it will be primarily viewed on mobile devices you can lower the resolution even further. While most mobile devices are capable of displaying very high-resolution images and video, the screens are obviously quite small so the reduced quality of a low-resolution video will not be as noticeable. For social media, a resolution of 720p, which is 1280 pixels by 720 pixels, might be a good choice.
For some social media platforms, such as Instagram, square videos work just as well. You can easily reduce the file size by cropping a 1920 x 1080 video file to a square 1080 pixels by 1080 pixels.
How to reduce the resolution of a video
The easiest way to reduce the resolution of a video in an editing program is during the export or encoding stage. When exporting, look for an option like “video dimensions” or “adjust width and height” to adjust the resolution. Keep in mind, if you change the dimension of the video it may crop or stretch the image to fit the new shape.
Reduce the bitrate of the video.
Reducing the bitrate is an easy way to reduce file size without shortening your video or changing the size of the image. However, it may not be the most intuitive unless you know what the ideal bitrate for your particular video resolution is.
For videos that will be streamed online, such as videos uploaded to YouTube, a good starting point is 8 Mbps (megabits per second) for 1080p videos and 5 Mbps for 720p videos (at standard frame rates). Social media platforms usually have restrictions on how large video uploads can be so 5 Mbps even for 1080p videos works well. You can play around with bitrate if the video is still too large—these numbers are just a jumping-off point.
Here’s how to reduce the bitrate of a video using most video editing software:
- Import and prepare your video in video editing software.
- During the Export/Render/Share step, look for a Bitrate setting. In some applications, such as Descript, this may appear as a more user-friendly Video Quality setting where you can select Low, Medium, or High. In other applications, you may have to type in the exact bitrate you desire.
- Select Variable Bitrate, or VBR, if that option is available.
- You may be given the choice between 1 pass encoding or 2 pass encoding when choosing VBR. 2-Pass Encoding may improve the video quality of the final render but will result in a longer encoding time (the time it takes the software to actually export the video file for you).
Convert the video to another format.
Some video formats and codecs compress data more efficiently. Converting your video to another format may be able to shave some of that extra size down. For example, a popular video format for online use is MP4 (or MPEG-4) using the H.265 (HEVC) codec. This particular format is well-regarded due to its high compression, good video quality, and compatibility. This may change as more codecs and formats are developed.
To convert a video to another format in a video editing program, simply select your desired format and codec during the export process. Common codecs besides MP4 include MKV, MOV, and WEBM.
Keep in mind that not every video may be suited to each format. Different codecs handle the compression process differently and you may find one format and codec struggles with your particular video while another retains more detail.
Compress your video online
There are also online video converter services that allow you to compress video without the need for video editing software. Some require you to sign up for an account or pay for a subscription to compress longer videos while others are free.
A few online video compression services:
The process is usually simple but varies between the specific options may vary. For example, Online Converter only has options to change the resolution of a video but the output will be limited to MP4.
Make a GIF
If the video you wish to share is short and the audio is not important, you could create a GIF. This is particularly viable if you wish to share the video on social media where GIFs run rampant.
There are many websites that allow you to convert a video to GIF including some of those mentioned in the last suggestion, such as Cloud Convert. There are also websites dedicated solely to the GIF format, like Giphy, that feature easy video-to-GIF conversion options.