Video Transcoding deals with converting a previously compressed video signal into another one with different format. Converting files to a different bit rate, frame rate, frame size, or even compression can be considered going through the process of Transcoding. Converting a compressed video stream from one format to another for transmission over Internet networks to an end device such as a cell phone or a computer is a common method. As in most streaming media companies the Transcoding procedure and technology is usually a free service.
In many applications efficient transcoding is crucial. For example, in order to support video-on-demand streaming, often video will be stored in one master format to save space but many different viewing devices and decoders will have to be supported. This can be done by transcoding the data just before it is delivered, at real-time or faster-than-real-time rates. In production, to edit video it is necessary to decode it, modify it, and re-encode it. In the home, to use video on a home video server, the video may have to be transcoded in order to support the formats supported by the server.
There are a number of reasons for transcoding your media. You may want to convert a high-quality original edit to a digital distribution format easily sent to customers over the Internet, like H.264/AAC in an MP4 container. Or you may want to convert your high-quality music library, stored in AAC or Vorbis, for your music player that only supports MP3 files. Often, you may want to target a specific platform or device, like Adobe Flash, that supports a limited set of formats and thus need to convert your media library to a suitable format for proper delivery. You may even have old MPEG2 HDV tapes that you want to transcode to H.264 High Profile to save 40% of the storage space while losing no noticeable quality.
Some things to keep in mind about transcoding:
- Transcoding always lowers quality
- Transcoding can take a long time, depending on formats and settings
- The newest formats and codecs are not always best
- Remember your intended audience and their decoding ability (e.g. phones)
How to Transcode
There are literally dozens of commonly used formats and many, many software packages that can handle converting between different formats for you, though the speed, quality, and supported input and output formats differ between much of the software. There are even online services setup specifically to transcode media for a fee. If you are willing to get your hands dirty it is quite easy to get free and open source tools that will handle most any format you throw at them.