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A video is two or more separate tracks—moving picture and audio—that each go through a compression algorithm. Otherwise, the resulting files would be huge, even for short videos. The compressed tracks then get wrapped up into a container file, what’s often called a wrapper. When you receive a file saved in a standard wrapper, such as .MOV for a QuickTime Movie file, you have no way to know for certain which codecs were used to compress the video or audio tracks inside that container file (Figure 20-28).

Figure 20-28 A standard container file holds multiple tracks, each encoded separately.

Codecs

Video files use standard audio codecs for the audio tracks, such as WAV or MP3, but vary wildly in the type of video codecs used. Just as with audio codecs, video codecs take a video stream and compress it by using various algorithms. Here are some of the standard video codecs.

MPEG-2 Part 2, used for DVDs

MPEG-4 Part 2, a codec often used for Internet broadcasts; you’ll find implementations of it with other names, such as DivX

H.264, used for high-definition movies for Blu-ray Discs, among others

Windows Media Video (WMV), the family of Microsoft-developed codecs

Theora, an open-source codec developed to go with the Vorbis audio codec as part of the Ogg project

TrueMotion VP6, used in Adobe Flash; and VP7, used for Skype video conferencing, among others

VC-1 is a Microsoft-designed codec that competes with H.264 and other higher-end codecs for the hearts and minds of Blu-ray Disc developers. You’ll usually find it wrapped in a WMV container file (see the following section).

Wrappers

When both the video and audio streams of your video file are compressed, the file is placed into some sort of container file or wrapper. The key thing to note here is that the wrapper file doesn’t necessarily specify how the video or audio tracks were encoded. You can look at two seemingly identical movie files, for example, both saved with the .MOV file extension, and find that one will play audio and video just fine in Windows Media Player, but the other one might play only the audio and not the video because Media Player lacks the specific codec needed to decode the video stream. (More on this in the “Troubleshooting” section.) Here are some of the standard video wrappers.

ASF, a container used mainly for WMA and WMV streams; note that you can also have a WMV wrapper for a WMV-format file.

AVI, the standard container file for Windows

Flash Video (.FLV) contains streams encoded with various codecs, such as H.263 or VP6; can also handle H.264 codec. Flash Video has become the dominant standard for displaying video content on the Web through places such as YouTube and Hulu.

MOV, the standard container file for Apple QuickTime for both Macintosh OS X and Windows

MPEG-2 Transport Stream (MPEG-TS), a container for broadcasting that can handle many streams

Ogg, a container file made for the open source Vorbis and Theora codecs

Troubleshooting

Video capture and playback suffer from several quirks. On the capture side, you’ll find dropped frames, problems synchronizing video and audio when capturing content from an analog device, and generally poor quality captures. On the playback side, the only real issue is missing codecs.

Dropped Frames

Many things cause an initial capture to drop frames, the end result of which is loss of video information and choppy playback. This happens with both analog and digital sources, so it’s not necessarily a conversion issue, and it’s maddeningly common.

The most common fix for dropped frames is to turn stuff off. Some of this is obvious. If you’re surfing the Web or doing instant messaging while trying to capture video, you’ll drop frames with wild abandon. Don’t do it. In fact, disconnect the computer completely from the Internet so no traffic happens in the background. Only do video capture on that machine and use another computer if you need to multitask.

Often the viewing of content you’re capturing