An Intermediate Codec is a video encoding format which is specifically designed to be used for editing and post-production.
Every professional editing workflow involves choosing an intermediate codec. For professional packages like Final Cut Pro, Avid, or Media 100, this is an explicit choice that is made by the editor using features of the editing package. For consumer packages like Windows Movie Maker, Sony Vegas, and others, intermediate codecs are used internally and the package attempts to hide the details of how such intermediate work is done. However, consumer packages do not deliver consistent quality throughout the editing workflow because the editor using the consumer package is often not aware (and cannot control) the source and destination materials using compatible codecs.
Intermediate codecs have the following characteristics:
- While they still use some video compression, they are designed specifically to preserve video content integrity as their highest priority. Therefore, video encoded with a good intermediate codec can suffer many "generations" (re-encodings) without significant quality loss. Distribution formats such as DV and H.264, by contrast, rapidly show degradation as re-encodes are performed.
- Intermediate codecs are designed for high-speed and low CPU usage. This makes them ideal for direct use within editing programs and for video capture. Codecs like H.264, for example, are the opposite extreme and consume enormous amounts of CPU during encoding. This means that using H.264 directly within editing sessions, or worse, for output, can cause dropped frames or other artifacts introduced by having a saturated CPU during editing.
- Intermediate codecs are designed to allow accurate interframe cuts. With other codecs, such as H.264, frames are "grouped" around keyframes. So, cuts done within editing programs are often "rounded" up or down to the nearest keyframe boundary. This can cause edits to gradually "drift" away from the intended position as projects are saved and reused.
- Intermediate codecs have well-defined chroma characteristics so that they preserve color information exactly.
Until 2007, obtaining a good intermediate codec was expensive. They were either bundled with high-end editing systems like Avid, or available separately from companies like Cineform. In 2007, Apple introduced ProRes 422, an excellent intermediate codec suitable for both television and HD cinema work which has gained a great deal of industry support and acceptance.
Here are some of the available intermediate codecs:
- Apple ProRes 422 - Works on Mac systems, free drivers available to read ProRes files on PC systems for use in PC-based work flow.
- CineForm - One of the first intermediate codecs designed as a Digital Intermediate. Available only under license. Works with packages like Premier and Final Cut.
- DNxHD - An excellent intermediate codec available from Avid. Works with Premier and Final Cut as well as all Avid systems of course.