- Are Your Video Files Too Big?
- Friday, September 12, 2008
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In this educational segment we are going to change pace a bit and concentrate on the area of video compression. We have received quite a few messages on our forum relating to this issue, so hopefully this weblog will help clear up some of the confusion regarding video compression.
Understanding video compression is important because uncompressed digital video can take up a staggering amount of room in its original form. By compressing the video, you make it easier to store. Without video compression, Internet video would simply not be possible. It’s that important. Video files are HUGE. Download times for raw, uncompressed video would be so high that no one would bother, even at broadband speeds.
An Introduction to Video Compression
A video (file types like AVI and MPEG) is a collection of several images being shown. Each image is called frames and the amount of images shown per second is called frames per second or simply FPS. The more frames per second your video has, the better, since more realistic the image will be. Videos are usually saved using at least TV quality settings, i.e. 30 frames per second. Have you ever exported a finished edit, only to find that the file was so big you couldn’t upload it to a website, send it to a friend, or even burn it on a dvd? Or maybe you’ve created a masterpiece, exported, and upon playback your video looks like a bunch of ugly blocks and spots. Understanding video compression and learning how to use it will help you overcome these problems.
What Is Video Compression?
Video compression is a process that reduces the amount of data contained in a video file, thus making the file smaller. It is possible to compress digital video because it contains redundant information. Imagine a tripod shot of a plane flying across a blue sky. The majority of the background remains the same from frame to frame. Instead of storing the sky data for every frame, a compressed video can re-use the sky data from a previous frame until there is a change. So if the background is unchanged for 12 frames, the information can be stored in 1 frame instead of 12. The process takes place with each individual pixel, not just frames. This allows for the most efficient reduction of data redundancy.
Does Video Compression Affect Video Quality?
Yes. By reducing the amount of video data, it’s only natural that details of the video are lost. Before you decide to give up on video compression though, take note that even DVDs contain compressed video. Generally, high quality video is less compressed and takes up more disk space. Compressing video for the internet can be a challenge because you want to make the file small while keeping quality as high as possible. We’ve all seen blocky videos on the internet, especially on sites like YouTube, where they automatically compress the clips you upload. With some testing and tweaking though, it is possible to create web videos that still look good.
Video Codecs and Compression
Video is compressed by software or devices called Codecs (Compressor-Decompressor). Each codec uses a unique algorithm to eliminate data redundancy and make the file smaller. If you have ever tried to play a downloaded video and had it fail, it may have been because your computer wasn’t equipped with the proper codec to interpret the video. Some popular codecs include DVIX, MPEG-1, MPEG-2, H.264, and WMV).
You can learn more about video terms and compressions from the following links: http://en.wikipedia.org/wiki/Video_compression, http://www.homemovieediting.co.uk/compression.html and http://www.wave-report.com/tutorials/VC.htm