Video Encoding

CompressionEncoding is just another term for data compression. Data (or file) compression is a cornerstone of our Internet-based world. Computer files take up hard drive space. Transferring computer files over the Internet takes time. The way that you save hard drive space or speed up the transfer of files is with file compression. Examples of file compression are JPEG images, DVDs (encoded as MPEG-2 video), MP3 audio files, and “Zip” archives. We’ll talk here about Video Encoding (video compression).

When you have finished editing your video, the editing programs allow you to save the video in a variety of formats, or share to a variety of video hosting sites such as YouTube or Vimeo. If you have a DVD recorder, you could create a DVD disc that can then be played in a home DVD player. If a video is not too long, you can even send it as an attachment in an email.

When you encode, or compress, a video in a particular format, you generally are taking something away, to make the file smaller. In general the quality will be lower. If you are encoding your video into a smaller physical dimension, called scaling, you will also generally make the file smaller. If you record video with a typical HD camcorder, the video will be 1920 x 1080 pixels. If we encode the video with smaller dimensions, say 640 by 360 pixels, that will result in a smaller size file on the hard drive. We can further reduce the “quality” settings and get an even smaller file. So what is this “Quality” setting anyway?

As we’ve said before, most video editing programs have the ability to save in multiple formats. When you save the file in a given format, it will ask you to specify a level of quality. If you want to distribute the file with virtually no quality loss, or save it for archiving purposes, you will likely use the highest quality setting. You may have some viewers using a high speed broadband connection, and a high-quality version would be appropriate for them too. However, if they have a lower speed connection, or a mobile device, you might offer a medium quality setting for them. If you want to email the file, then a lower quality setting would be appropriate.

If you upload your video to YouTube, it will be automatically encoded at several different sizes, or resolutions. This will allow people to see your video on many different types of devices – from computers, to media devices (Roku or Apple TV), to tablets, to mobile phones. YouTube supports up to 4K resolution (3840×2160) video, but will also will encode in 1080p (1920×1080), 720p (1280×720), 480p, 360p, 240p, and 144p. While these are not “quality” settings per se, the 1080p version will appear “sharper” than the lower resolution versions when you watch them on your computer screen (especially at full screen size). The differences will be less noticeable on a smaller-screened device like a tablet, or a mobile phone.

Just keep in mind that video at a given resolution is not always equal. Something called bit rate will govern the quality at a particular resolution. For example, the bit rate of a 1080p movie on a Blu-ray disc will be much higher than the bit rate of a video you would watch on Netflix or YouTube. The movie file would also be significantly larger on the Blu-ray disc. The following images will give you an idea of how high quality (high bit rates) will differ from medium and low quality (lower bit rates). The fuzziness around the text is known as artifacting, and it gets more pronounced as you choose lower and lower quality settings. You’ll notice that colors also start to become less vibrant.

High Quality (high bit rate)

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Medium Quality

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Low Quality (low bit rate)

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There are a few standalone compression programs that are worth mentioning that will convert a video to another format. Two of our favorites are Handbrake (Mac and Windows) which specializes in converting DVDs to MPEG4 video, and Miro Video Converter, a more all-purpose converter, including audio conversion. Handbrake uses the x.264 codec which is a fully compatible version of the h.264 codec. It allows you to save videos for devices like the iPhone, the iPod Touch, and the Apple TV. Miro Video Converter uses a different compression “library” called FFmpeg. Again, it allows a greater variety of input and output formats.

cc licensed flickr photo shared by CoreyHarris

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