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Digital Video Formats
Tape Brands
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| VCD |
Mpeg-1- |
CBR 1150, 352x240 |
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| SVCD |
Mpeg-2 |
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Mpeg-4 |
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WMV |
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FLV |
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SWF |
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MOV |
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Introduction and Disclaimer...Akkana Peck
Link
I am not an expert in video formats. I wrote this page because I was having
trouble getting the information, and couldn't find any good explanations of
video formats on the web. The information here is gleaned from reading pages I
found via google searches (references to some of the useful sites I found are
given at the bottom).
This is a work in progress. If you find errors, please
let me know.
What's a Video Format?
Video formats are confusing because most video files have at least two different
types: the container, and the codec(s) used inside that container.
The container describes the structure of the file: where the various
pieces are stored, how they are interleaved, and which codecs are used by which
pieces. It may specify an audio codec as well as video.
A codec ("coder/decoder") is a way of encoding audio or video into a
stream of bytes.
To make life even more confusing, some names, such as "mpeg-4", describe both a
codec and a container, so it's not always clear from context which is being
used. You could have a movie encoded with an mpeg-4 codec inside an avi
container, for example, or a movie encoded with the Sorenson codec inside an
mpeg-4 container.
The Linux file program is a fast way to find out the container format of
a video file.
You can use the mencoder program (part of mplayer) to tell you the
container and video codec of a file (you'll have to wade through a lot of other
output).
For mpeg files, you can find out the audio codec with mpginfo, part of
the mpgtx package. For other formats, try
mplayer -identify -frames 0 filename | grep ID_
Common Container Formats:
AVI (.avi): Most commonly contains M-JPEG (especially from digital cameras?) or
DivX (for whole movies), but can contain nearly any format (not Sorenson).
Sometimes you'll see a reference to the "fourcc": this is a four-character code
(such as "divx" or "mjpg") inside the AVI container which specifies which video
codec is being used.
Quicktime: Most often used for the locked Apple Sorenson codec, or for Cinepak
(free), but can also hold other codecs such as mjpeg, etc.
WMV (.wmv): More or less MPEG4; can contain nearly any codec, including several
Microsoft spinoffs of MPEG-4 which vary in their freedom and licensing
requirements.
ASF ("Advanced Streaming Format", .asf): a subset of wmv, intended primarily for
streaming: an early Microsoft implementation of an MPEG4 codec.
Common Codecs:
MPEG ("Moving Pictures Expert Group"): three video formats, MPEG 1, 2, and 4.
MPEG-1: Old, supported by everything (at least up to 352x240), reasonably
efficient. A good format for the web.
MPEG-2: A souped-up version of MPEG-1, with better compression. 720x480. Used
in HDTV, DVD, and SVCD.
MPEG-4: A family of codecs, some of which are open, others Microsoft
proprietary.
MPEG spinoffs: mp3 (for music) and VideoCD.
MJPEG ("Motion JPEG"): A codec consisting of a stream of JPEG images. Common in
video from digital cameras, and a reasonable format for editing videos, but it
doesn't compress well, so it's not good for web distribution.
DV ("Digital Video"): Usually used for video grabbed via firewire off a video
camera. Fixed at 720x480 @ 29.97FPS, or 720x576 @ 25 FPS. Not very highly
compressed.
WMV ("Windows Media Video"): A collection of Microsoft proprietary video
codecs. Since version 7, it has used a special version of MPEG4.
RM ("Real Media"): a closed codec developed by Real Networks for streaming video
and audio. Maybe also a container?
DivX: in early versions, essentially an ASF (incomplete early MPEG-4) codec
inside an AVI container; DivX 4 and later are a more full MPEG-4 codec.. No
resolution limit. Requires more horsepower to play than mpeg1, but less than
mpeg2. Hard to find mac and windows players.
Sorenson 3: Apple's proprietary codec, commonly used for distributing movie
trailers (inside a quicktime container).
Quicktime 6: Apple's implementation of an MPEG4 codec.
RP9: a very efficient streaming proprietary codec from Real (not MPEG4).
WMV9: a proprietary, non-MPEG4 codec from Microsoft.
Ogg Theora: A relatively new open format from
Xiph.org.
Dirac: A very new open format under development by the
BBC.
There are many others; this document does not attempt to list them all.
References
Advanced
Video Compression - Part 1 and
Part 2.
A most excellent overview.
Codec/Container
Table -- The page is partly in French, but the table is in English.
Linux A/V (Co)Decs --
says it's out of date, but a useful table nontheless, showing containers,
codecs, and players which support them.
FAQ of AVI MPEG Video Converter
FourCC list of video codecs
Still Image Formats for
the Web
Linux Information
Shallow Sky Home
Contact Akkana
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