DIGITAL VIDEO FORMATS
Page 1: Introduction (this page)
Page 2: AVI files and associated compression algorithms
Page 3: MPEG-1
Page 4: MPEG-2
Page 5: MPEG-4
Page 6: DV-AVI
Page 7: Microsoft WMV, WMA, and ASF
Page 8: Real Media
Page 9: Transmission and Recording Standards: DV (tape and FireWire), Cable, and Satellite
Page 10: Notes on various Video and Audio Coding Standards
Appendix: My letter to Widescreen Review about MPEG-4
Digitally encoded video
material (including associated audio tracks) may be stored on tape, disc, memory
card (such as a SmartMedia card), or on a PC’s hard-drive.
It may also be transmitted over a communications link, such as a
satellite TV downlink, a cable TV system, or a FireWire link between two
devices. When stored on
random-access media (disc, card, or hard-drive), digital video material is
generally organized into files. On
a tape, or on a continuous feed over a communications link, there is no file
structure but the material is generally organized into frames to allow the
receiving end to find a starting point for interpreting the bits.
(This continuous-stream situation should not be confused with the use of
a communications link to copy a file of digital video material between one PC
and another, where a file-transfer protocol copies the file as a complete unit
across the link, using a file-transfer protocol.)
digitalized video and audio signals are created from the analog signals
generated by the camera and microphones in a TV studio or camcorder, or
generated by a film-to-video convertor. Before
these signals are stored or transmitted they are often processed through a
compression algorithm to reduce the total number of bits to be
stored/transmitted. But in a few
special cases the “raw” uncompressed digital streams are maintained.
Uncompressed video is used in the creation of high-quality digital
“masters” for digitally-shot movies or TV shows, and in the creation of
digital masters from traditionally-shot films.
algorithms are in widespread use, including DV, MPEG-1, MPEG-2, and MPEG-4.
These vary in terms of the efficiency with which they compress the video
information. MPEG-2 (used on DVDs
and most satellite and cable TV systems) is more efficient than the older MPEG-1
(used on VCDs), and MPEG-4 is more efficient than MPEG-2.
DV is, by design, the least efficient algorithm.
It was designed so that it reduced the bit-rate just enough to make
storage on tape and transmission over FireWire easier, while maintaining
high-quality discrete images for each video frame.
The resulting material is typically edited before a more aggressive
compression algorithm is applied.
When stored as a file,
digital video material (including associated audio material) generally has the
The video and audio components are
interleaved in some way, so that any section of the file can be easily played
without making the job of accurately aligning the timing of the extracted video
and audio components needlessly difficult.
The file has a name using the
standard computer format “name.extension”.
§ The file contains header information that identifies the compression algorithm (if any) that has been used in preparing the information for the file. (Note that, in some cases, a file extension such as “.mpg” or “.vob” may also indicate which algorithm has been used for compression. However, extensions like “.avi” are not unique to one algorithm. Where the extension and the information in the file header are in conflict, most video players will ignore the extension and follow the header information.)
AVI files and associated compression algorithms
Or go direct to...
MPEG-4 [Also: See My letter to Widescreen Review about MPEG-4]
Microsoft WMV, WMA, and ASF
Transmission and Recording Standards: DV (tape and FireWire), Cable, and Satellite
Notes on various Video and Audio Coding Standards