Digital Video Quick Reference

Terminology

container format: a method for combining multiple data streams into a single file
codec: a method for representing digital information (typically video, audio, or a still image) as a digital data stream
fps: frames per second
frame: a single image in a video stream
resolution: the dimensions of a frame in a video stream (typically the same for all frames in a stream)
aspect ratio: the ratio of an image's width to its height
interlacing: frames are displayed by putting pixels on the screen alternately in all even rows and all odd rows (mostly obsolete)
progressive scan: frames are displayed by putting pixels on the screen left-to-right and top-to-bottom, like reading English text
1080p: 1080-row frames, progressive scan; 16:9 aspect ratio is implied, giving a horizontal dimension of 1920. frame rate is often 60 fps, but not always
DVD: A disc that is read by a red laser and can contain any data. A DVD containing specific types of video and audio data in a specific layout can be played in a standard DVD player.
Blu-Ray: A disc that is read by a blue laser and can contain much more data than a DVD. A Blu-Ray containing specific types of video and audio data in a specific layout can be played in a standard Blu-Ray player.

See Wikipedia for a more complete list.

MP4: Defined in the MPEG4 specification, this format is common on the Internet. It is best used with MPEG-4 or H.264 video
Matroska (MKV): Very flexible but not as widely supported as MP4 or AVI, this container can hold almost anything.
WebM: WebM isn't actually a container format itself, but a particular combination of container and codecs: Matroska (with certain features deemed off-limits), VP8, and Vorbis. It is designed to be easy to support without paying patent royalties to anyone, but support for it is still a bit spotty. The WebM specification was created by Google.
AVI: Supported nearly everywhere but not very flexible, AVI is the container format of choice for video that absolutely must run on everything under the sun, although it is rapidly being eclipsed by MP4.
VOB: Based on MPEG-2 Program Stream (MPEG PS), this format is used on DVDs and pretty much nowhere else.
3GP: 3GP is most commonly seen on mobile phones.
MPEG Transport Stream: This format is seen on Blu-Ray discs and newer digital video cameras (typically holding H.264 video) and broadcast HDTV (typically holding MPEG-2 video). Most modern video editing software supports it.
Ogg: This format is typically seen holding just Vorbis audio (sometimes Theora video, too). It is royalty-free, which made it popular in the free software community.

See Wikipedia for a more complete list.

MPEG-4: Very commonly used on the Internet, MPEG-4 provides good compression with relatively low complexity.
H.264: An evolution of MPEG-4, H.264 is widely used where small file size is more important than complexity (or where specialized hardware is available to shoulder the burden of decoding it).
VP8: VP8 is rising in popularity due to its inclusion in the WebM standard and the lack of any patent royalties for its use, but support is still a bit spotty.
MPEG-2: Primarily used in DVDs and broadcast HDTV, MPEG2 offers decent compression with fairly low complexity. Its patent licensing terms are somewhat burdensome, so many computers do not have any software that can play it.
Theora: Theora is based on VP3, a predecessor of VP8. It is most popular in the free software community due to its lack of patent royalties. It has begun to fall out of favor due to the availability of the technically superior VP8.

See Wikipedia for a more complete list.

MP3: This is the codec that started the digital music revolution. It provides decent compression with low complexity.
AAC: Part of the MPEG-4 standard, this codec is often found in MP4 files and songs purchased from iTunes. It provides better compression than MP3.
Vorbis: Typically found inside an Ogg container (although increasing also found in WebM files), this codec provides better compression than MP3. Like Ogg, it is royalty-free.
FLAC: FLAC is a lossless compression scheme. That means that the data that comes out is exactly the same as what went in. The downside is that it doesn't compress nearly as well as MP3. It is typically only used by digital music enthusiasts, although many cheap portable music players can play it.
ALAC: ALAC is Apple's lossless audio codec. It is rarely seen outside the music collections of digital music enthusiasts who are also Apple enthusiasts.
AC-3: Also known as Dolby Digital or A/52, AC-3 is typically found on commercial DVDs and Blu-Ray discs. It allows for multiple audio channels, which enables surround-sound support.
DTS: DTS is typically found on commercial DVDs and Blu-Ray discs. It allows for multiple audio channels, which enables surround-sound support.

If you have trouble playing a video file, try VLC. Its user interface isn't the friendliest in the world, but it can play nearly anything.