A few months ago, a customer wrote in saying that he had a new camera that only took movies in AVI format, which he couldn’t watch on his Mac. He was getting audio but no video, along with the message that “Quicktime parts are missing.”
Quicktime can play .AVI (Audio Video Interleave) files. According to Apple, the .AVI format is known as a “container format.” It specifies a way in which a file may contain audio and video data, but does not specify how that data is encoded.
The encoding of audio and video data is specified in what are known as codecs. A codec (short for COmpressor/DECompressor) tells the computer how to decode the audio and video tracks that have been encoded within the .AVI file.
When QuickTime opens an .AVI file, it checks to see which codecs were used to encode the audio and video tracks within it. For example, an .AVI file may contain a video track encoded in the Cinepak codec and an audio track encoded with the ALaw 2:1 codec. If both the audio and the video were compressed using a codec that QuickTime can use, the file will play normally. If the audio or video or both were created using codecs that QuickTime cannot use, you may see the “Quicktime parts are missing” message mentioned above.
You can see a list of audio and video codecs included with and supported by QuickTime by clicking here
QuickTime Player can use dozens of codecs by default. Note that you can also easily add additional codecs to extend QuickTime’s features using plug-ins or third-party installations. For example, DIVX is a popular video format that can be played by via Quicktime, once a plug-in is installed.