Codecs - Video Compression Formats
Compressing video is a trade-off between quality and file size. Uncompressed video takes up massive volumes of storage space on computers. To save space, storing video requires compression and playing the video back requires decompression.
Video Compression Algorithms (known as Codecs) – Codecs stands for Compressors/decompressors and they were devised to handle the compression of video for storage and decompression for playback.
Codecs compress video and audio by looking at consecutive frames and removing redundant data. Static shots (talking heads) have greater redundant data than an action scene. The compression process can take some time and heaps of computer processing power. However, decompression takes place in real time as the video is being played back.
Many codecs use what is called lossy compression, which means that it removes redundant data from the original movie. Therefore, you should never compress a movie multiple times because each pass will remove more data and the quality will be lower.
Encoding
A process that converts video/audio media into a file that is viewable on a number of different mediums, i.e., the Internet and DVD. Encoding compresses the video.
The highest quality of compressed video requires the highest quality source material. It’s best to encode from a master or the highest quality edit you have.
Web-Delivered Video
Web video is viewed in a smaller window, the frame rates are slower, and often the resolution is lower. The lower quality is the result of a smaller file size.
Choosing a Codec
This depends on the source material. Video that changes little frame by frame (greater redundancy) will compress better than video with action (lesser redundancy). For example, a talking head video has little change (greater redundancy). The less detail there is in the image the better the codec is able to compress it.
Bit Rates
Determined by the frame redundancy. A talking head video (greater redundancy) requires a lower bit rate, but a high-speed action scene (lesser redundancy) requires a faster bit rate because there are fewer redundant bits to discard. Another way to look at it: a low bit-rate will cause more compression artefacts (e.g., blockiness) in the action scene than in a static scene.
Popular Codecs
MPEG – this is a format and a codec at the same time. There are different “flavours” of MPEG that can be converted into QuickTime, which essentially makes MPEG’s playable using QuickTime players.
MPEG-2 – provides broadcast quality video and audio and is ideal for backpack journalists who need to send video back to TV stations. MPEG-2 is the primary video standard for DVD’s. The playback generally requires special hardware that is built into DVD players and most DVD-ROMs in computers. However, MPEG-2 is not appropriate for use as Web video. MPEG-2 can store redundant data more efficiently, making it virtually indistinguishable from the uncompressed video source.
MPEG-3 – also known as MP3 is a codec used for compressing audio.
MPEG-4 – a relatively newer form of MPEG standard that is designed for Internet connections. The codec includes audio and video. The video is similar to H.263 and H.264, but is more optimised for delivery at Internet data rates. Both QuickTime and Windows Media can create and playback MPEG-4 video.
H.263 – a standard video-conferencing codec, optimised for low data rates and relatively low motion. Great for talking heads! This codec was designed to deliver better quality below 64 kbit/sec.
H.264 – is being used more than H.263, delivering better video quality at somewhat low data rates. The quality is good along several bandwidths – from 3G mobile phones to DVD’s and even HD.
Flash Video – used often by YouTube and My-Space, although sometimes given a bad name for its low video quality on YouTube. Flash can convert video that is often used on computers. There are two common extensions: FLV (flash video) is a streamed file and the format used by YouTube, which can easily be loaded onto the web. SWF doesn’t require an embedded player and cannot be edited.
Photo-JPEG – produces movies with excellent image quality, though it is a lossy codec. However, this codec requires extensive amounts of computer power for playback. It’s well-suited for slideshows that use low frame rates and no special video transitions like dissolves.
Video and Audio Compression Applications
Autodesk’s Cleaner (formerly known as Media Cleaner) is the industry standard for compression applications for media professionals. Not for beginners! Cleaner is available for both Mac and PC.
Final Cut Pro’s Compressor can give a set of parameters that fit your distribution needs.
QuickTime Pro can also compress video.
Sorenson Squeeze is good for beginners that gives advanced compression for the web.
VLC, or VideoLan, is an open-source cross-platform multimedia player that can play most multimedia files as well as DVD, Audio CD, and various streaming protocols.
MPEG Streamclip – another free converter, player and editor for Mac and Windows, it can convert MPEG files, encode movies to many formats, including iPod, it can cut, trim and join movies and can also download movies from YouTube and Google by entering the URL page.
Click here to learn how MPEG Streamclip works