Content format for digital video content
A
video coding format
[a]
(or sometimes
video compression format
) is a
content representation format
of
digital video
content, such as in a data file or
bitstream
. It typically uses a standardized
video compression
algorithm, most commonly based on
discrete cosine transform
(DCT) coding and
motion compensation
. A specific software,
firmware
, or hardware implementation capable of compression or decompression in a specific video coding format is called a
video codec
.
Some video coding formats are documented by a detailed
technical specification
document known as a
video coding specification
. Some such specifications are written and approved by
standardization organizations
as
technical standards
, and are thus known as a
video coding standard
. There are
de facto
standards
and formal standards.
Video content encoded using a particular video coding format is normally bundled with an audio stream (encoded using an
audio coding format
) inside a
multimedia container format
such as
AVI
,
MP4
,
FLV
,
RealMedia
, or
Matroska
. As such, the user normally does not have a
H.264
file, but instead has a
video file
which is an MP4 container of H.264-encoded video, normally alongside
AAC
-encoded audio. Multimedia container formats can contain one of several different video coding formats; for example the MP4 container format can contain video coding formats such as
MPEG-2 Part 2
or H.264. Another example is the initial specification for the file type
WebM
, which specifies the container format (Matroska), but also exactly which video (
VP8
) and audio (
Vorbis
) compression format is inside the Matroska container, even though Matroska is capable of containing
VP9
video, and
Opus
audio support was later added to the
WebM
specification.
Distinction between
format
and
codec
[
edit
]
A
format
is the layout plan for data produced or consumed by a
codec
.
Although video coding formats such as H.264 are sometimes referred to as
codecs
, there is a clear conceptual difference between a specification and its implementations. Video coding formats are described in specifications, and software,
firmware
, or hardware to encode/decode data in a given video coding format from/to uncompressed video are implementations of those specifications. As an analogy, the video coding format
H.264
(specification) is to the
codec
OpenH264
(specific implementation) what the
C Programming Language
(specification) is to the compiler
GCC
(specific implementation). Note that for each specification (e.g.
H.264
), there can be many codecs implementing that specification (e.g.
x264
, OpenH264,
H.264/MPEG-4 AVC products and implementations
).
This distinction is not consistently reflected terminologically in the literature. The H.264 specification calls
H.261
,
H.262
,
H.263
, and
H.264
video coding standards
and does not contain the word
codec
.
[2]
The
Alliance for Open Media
clearly distinguishes between the
AV1
video coding format and the accompanying codec they are developing, but calls the video coding format itself a
video codec
specification
.
[3]
The
VP9
specification calls the video coding format VP9 itself a
codec
.
[4]
As an example of conflation, Chromium's
[5]
and Mozilla's
[6]
pages listing their video format support both call video coding formats such as H.264
codecs
. As another example, in Cisco's announcement of a free-as-in-beer video codec, the press release refers to the H.264 video coding format as a
codec
("choice of a common video codec"), but calls Cisco's implementation of a H.264 encoder/decoder a
codec
shortly thereafter ("open-source our H.264 codec").
[7]
A video coding format does not dictate all
algorithms
used by a
codec
implementing the format. For example, a large part of how video compression typically works is by finding
similarities between video frames
(block-matching), and then achieving compression by copying previously-coded similar subimages (such as
macroblocks
) and adding small differences when necessary. Finding optimal combinations of such predictors and differences is an
NP-hard
problem,
[8]
meaning that it is practically impossible to find an optimal solution. Though the video coding format must support such compression across frames in the bitstream format, by not needlessly mandating specific algorithms for finding such block-matches and other encoding steps, the codecs implementing the video coding specification have some freedom to optimize and innovate in their choice of algorithms. For example, section 0.5 of the H.264 specification says that encoding algorithms are not part of the specification.
[2]
Free choice of algorithm also allows different
space?time complexity
trade-offs for the same video coding format, so a live feed can use a fast but space-inefficient algorithm, and a one-time
DVD
encoding for later mass production can trade long encoding-time for space-efficient encoding.
History
[
edit
]
The concept of
analog video
compression dates back to 1929, when R.D. Kell in
Britain
proposed the concept of transmitting only the portions of the scene that changed from frame-to-frame. The concept of
digital video
compression dates back to 1952, when
Bell Labs
researchers B.M. Oliver and
C.W. Harrison
proposed the use of
differential pulse-code modulation
(DPCM) in video coding. In 1959, the concept of
inter-frame
motion compensation
was proposed by
NHK
researchers Y. Taki, M. Hatori and S. Tanaka, who proposed predictive inter-frame video coding in the
temporal dimension
.
[9]
In 1967,
University of London
researchers A.H. Robinson and C. Cherry proposed
run-length encoding
(RLE), a
lossless compression
scheme, to reduce the transmission bandwidth of
analog television
signals.
[10]
The earliest digital video coding algorithms were either for
uncompressed video
or used
lossless compression
, both methods inefficient and impractical for digital video coding.
[11]
[12]
Digital video was introduced in the 1970s,
[11]
initially using uncompressed
pulse-code modulation
(PCM) requiring high
bitrates
around 45?200
Mbit/s
for
standard-definition
(SD) video,
[11]
[12]
which was up to 2,000 times greater than the
telecommunication
bandwidth
(up to 100
kbit/s
) available until the 1990s.
[12]
Similarly, uncompressed
high-definition
(HD)
1080p
video requires bitrates exceeding 1
Gbit/s
, significantly greater than the bandwidth available in the 2000s.
[13]
Motion-compensated DCT
[
edit
]
Practical
video compression
emerged with the development of
motion-compensated
DCT
(MC DCT) coding,
[12]
[11]
also called block motion compensation (BMC)
[9]
or DCT motion compensation. This is a hybrid coding algorithm,
[9]
which combines two key
data compression
techniques:
discrete cosine transform
(DCT) coding
[12]
[11]
in the
spatial dimension
, and predictive
motion compensation
in the
temporal dimension
.
[9]
DCT coding is a
lossy
block compression
transform coding
technique that was first proposed by
Nasir Ahmed
, who initially intended it for
image compression
, while he was working at
Kansas State University
in 1972. It was then developed into a practical image compression algorithm by Ahmed with T. Natarajan and
K. R. Rao
at the
University of Texas
in 1973, and was published in 1974.
[14]
[15]
[16]
The other key development was motion-compensated hybrid coding.
[9]
In 1974, Ali Habibi at the
University of Southern California
introduced hybrid coding,
[17]
[18]
[19]
which combines predictive coding with transform coding.
[9]
[20]
He examined several transform coding techniques, including the DCT,
Hadamard transform
,
Fourier transform
, slant transform, and
Karhunen-Loeve transform
.
[17]
However, his algorithm was initially limited to
intra-frame
coding in the spatial dimension. In 1975, John A. Roese and Guner S. Robinson extended Habibi's hybrid coding algorithm to the temporal dimension, using transform coding in the spatial dimension and predictive coding in the temporal dimension, developing
inter-frame
motion-compensated hybrid coding.
[9]
[21]
For the spatial transform coding, they experimented with different transforms, including the DCT and the
fast Fourier transform
(FFT), developing inter-frame hybrid coders for them, and found that the DCT is the most efficient due to its reduced complexity, capable of compressing image data down to 0.25-
bit
per
pixel
for a
videotelephone
scene with image quality comparable to a typical intra-frame coder requiring 2-bit per pixel.
[22]
[21]
The DCT was applied to video encoding by Wen-Hsiung Chen,
[23]
who developed a fast DCT algorithm with C.H. Smith and S.C. Fralick in 1977,
[24]
[25]
and founded
Compression Labs
to commercialize DCT technology.
[23]
In 1979,
Anil K. Jain
and Jaswant R. Jain further developed motion-compensated DCT video compression.
[26]
[9]
This led to Chen developing a practical video compression algorithm, called motion-compensated DCT or adaptive scene coding, in 1981.
[9]
Motion-compensated DCT later became the standard coding technique for video compression from the late 1980s onwards.
[11]
[27]
Video coding standards
[
edit
]
The first digital video coding standard was
H.120
, developed by the
CCITT
(now ITU-T) in 1984.
[28]
H.120 was not usable in practice, as its performance was too poor.
[28]
H.120 used motion-compensated DPCM coding,
[9]
a lossless compression algorithm that was inefficient for video coding.
[11]
During the late 1980s, a number of companies began experimenting with
discrete cosine transform
(DCT) coding, a much more efficient form of compression for video coding. The CCITT received 14 proposals for DCT-based video compression formats, in contrast to a single proposal based on
vector quantization
(VQ) compression. The
H.261
standard was developed based on motion-compensated DCT compression.
[11]
[27]
H.261 was the first practical video coding standard,
[28]
and uses
patents
licensed from a number of companies, including
Hitachi
,
PictureTel
,
NTT
,
BT
, and
Toshiba
, among others.
[29]
Since H.261, motion-compensated DCT compression has been adopted by all the major video coding standards (including the
H.26x
and
MPEG
formats) that followed.
[11]
[27]
MPEG-1
, developed by the
Moving Picture Experts Group
(MPEG), followed in 1991, and it was designed to compress
VHS
-quality video.
[28]
It was succeeded in 1994 by
MPEG-2
/
H.262
,
[28]
which was developed with patents licensed from a number of companies, primarily
Sony
,
Thomson
and
Mitsubishi Electric
.
[30]
MPEG-2 became the standard video format for
DVD
and
SD digital television
.
[28]
Its motion-compensated DCT algorithm was able to achieve a
compression ratio
of up to 100:1, enabling the development of
digital media
technologies such as
video on demand
(VOD)
[12]
and
high-definition television
(HDTV).
[31]
In 1999, it was followed by
MPEG-4
/
H.263
, which was a major leap forward for video compression technology.
[28]
It uses patents licensed from a number of companies, primarily Mitsubishi,
Hitachi
and
Panasonic
.
[32]
The most widely used video coding format as of 2019
[update]
is
H.264/MPEG-4 AVC
.
[33]
It was developed in 2003, and uses patents licensed from a number of organizations, primarily Panasonic,
Godo Kaisha IP Bridge
and
LG Electronics
.
[34]
In contrast to the standard DCT used by its predecessors, AVC uses the
integer DCT
.
[23]
[35]
H.264 is one of the video encoding standards for
Blu-ray Discs
; all Blu-ray Disc players must be able to decode H.264. It is also widely used by streaming internet sources, such as videos from
YouTube
,
Netflix
,
Vimeo
, and the
iTunes Store
, web software such as the
Adobe Flash Player
and
Microsoft Silverlight
, and also various
HDTV
broadcasts over terrestrial (
ATSC standards
,
ISDB-T
,
DVB-T
or
DVB-T2
), cable (
DVB-C
), and satellite (
DVB-S2
).
[36]
A main problem for many video coding formats has been
patents
, making it expensive to use or potentially risking a patent lawsuit due to
submarine patents
. The motivation behind many recently designed video coding formats such as
Theora
,
VP8
, and
VP9
have been to create a (
libre
) video coding standard covered only by royalty-free patents.
[37]
Patent status has also been a major point of contention for the choice of which video formats the mainstream
web browsers
will support inside the
HTML video
tag.
The current-generation video coding format is
HEVC
(H.265), introduced in 2013. AVC uses the integer DCT with 4x4 and 8x8 block sizes, and HEVC uses integer DCT and
DST
transforms with varied block sizes between 4x4 and 32x32.
[38]
HEVC is heavily patented, mostly by
Samsung Electronics
,
GE
,
NTT
, and
JVCKenwood
.
[39]
It is challenged by the
AV1
format, intended for free license. As of 2019
[update]
, AVC is by far the most commonly used format for the recording, compression, and distribution of video content, used by 91% of video developers, followed by HEVC which is used by 43% of developers.
[33]
List of video coding standards
[
edit
]
Timeline of international video compression standards
Basic algorithm
|
Video coding standard
|
Year
|
Publishers
|
Committees
|
Licensors
|
Market presence
(2019)
[33]
|
Popular implementations
|
DPCM
|
H.120
|
1984
|
CCITT
|
VCEG
|
?
|
?
|
Unknown
|
DCT
|
H.261
|
1988
|
CCITT
|
VCEG
|
Hitachi
,
PictureTel
,
NTT
,
BT
,
Toshiba
,
etc.
[29]
|
?
|
Videoconferencing
,
videotelephony
|
Motion JPEG
(MJPEG)
|
1992
|
JPEG
|
JPEG
|
ISO
/
Open Source does NOT mean free!
[40]
|
?
|
QuickTime
|
MPEG-1 Part 2
|
1993
|
ISO
,
IEC
|
MPEG
|
Fujitsu
,
IBM
,
Matsushita
,
etc.
[41]
|
?
|
Video CD
,
Internet video
|
H.262 / MPEG-2 Part 2
(MPEG-2 Video)
|
1995
|
ISO, IEC,
ITU-T
|
MPEG, VCEG
|
Sony
,
Thomson
,
Mitsubishi
,
etc.
[30]
|
29%
|
DVD Video
,
Blu-ray
,
DVB
,
ATSC
,
SVCD
,
SDTV
|
DV
|
1995
|
IEC
|
IEC
|
Sony,
Panasonic
|
Unknown
|
Camcorders
,
digital cassettes
|
H.263
|
1996
|
ITU-T
|
VCEG
|
Mitsubishi,
Hitachi
, Panasonic,
etc.
[32]
|
Unknown
|
Videoconferencing, videotelephony,
H.320
,
ISDN
,
[42]
[43]
mobile video
(
3GP
),
MPEG-4 Visual
|
MPEG-4 Part 2
(MPEG-4 Visual)
|
1999
|
ISO, IEC
|
MPEG
|
Mitsubishi, Hitachi, Panasonic,
etc.
[32]
|
Unknown
|
Internet video,
DivX
,
Xvid
|
DWT
|
Motion JPEG 2000
(MJ2)
|
2001
|
JPEG
[44]
|
JPEG
[45]
|
?
|
Unknown
|
Digital cinema
[46]
|
DCT
|
Advanced Video Coding
(H.264 /
MPEG-4
AVC)
|
2003
|
ISO, IEC, ITU-T
|
MPEG, VCEG
|
Panasonic,
Godo Kaisha IP Bridge
,
LG
,
etc.
[34]
|
91%
|
Blu-ray
,
HD DVD
,
HDTV
(
DVB
,
ATSC
),
video streaming
(
YouTube
,
Netflix
,
Vimeo
),
iTunes Store
,
iPod Video
,
Apple TV
, videoconferencing,
Flash Player
,
Silverlight
,
VOD
|
Theora
|
2004
|
Xiph
|
Xiph
|
?
|
Unknown
|
Internet video,
web browsers
|
VC-1
|
2006
|
SMPTE
|
SMPTE
|
Microsoft
, Panasonic, LG,
Samsung
,
etc.
[47]
|
Unknown
|
Blu-ray, Internet video
|
Apple ProRes
|
2007
|
Apple
|
Apple
|
Apple
|
Unknown
|
Video production
,
post-production
|
High Efficiency Video Coding
(H.265 /
MPEG-H
HEVC)
|
2013
|
ISO, IEC, ITU-T
|
MPEG, VCEG
|
Samsung,
GE
,
NTT
,
JVCKenwood
,
etc.
[39]
[48]
|
43%
|
UHD Blu-ray
, DVB,
ATSC 3.0
,
UHD
streaming,
HEIF
,
macOS High Sierra
,
iOS 11
|
AV1
|
2018
|
AOMedia
|
AOMedia
|
?
|
7%
|
HTML video
|
Versatile Video Coding
(VVC / H.266)
|
2020
|
JVET
|
JVET
|
Unknown
|
?
|
?
|
Lossless, lossy, and uncompressed
[
edit
]
Consumer video is generally compressed using
lossy
video codecs
, since that results in significantly smaller files than
lossless
compression. Some video coding formats designed explicitly for either lossy or lossless compression, and some video coding formats such as
Dirac
and
H.264
support both.
[49]
Uncompressed video
formats, such as
Clean HDMI
, is a form of lossless video used in some circumstances such as when sending video to a display over a
HDMI
connection. Some high-end cameras can also capture video directly in this format.
Intra-frame
[
edit
]
Interframe compression complicates editing of an encoded video sequence.
[50]
One subclass of relatively simple video coding formats are the
intra-frame
video formats, such as
DV
, in which each frame of the video stream is compressed independently without referring to other frames in the stream, and no attempt is made to take advantage of correlations between successive pictures over time for better compression. One example is
Motion JPEG
, which is simply a sequence of individually
JPEG
-compressed images. This approach is quick and simple, at the expense of the encoded video being much larger than a video coding format supporting
Inter frame
coding.
Because interframe compression copies data from one frame to another, if the original frame is simply cut out (or lost in transmission), the following frames cannot be reconstructed properly. Making 'cuts' in intraframe-compressed video while
video editing
is almost as easy as editing uncompressed video: one finds the beginning and ending of each frame, and simply copies bit-for-bit each frame that one wants to keep, and discards the frames one does not want. Another difference between intraframe and interframe compression is that, with intraframe systems, each frame uses a similar amount of data. In most interframe systems, certain frames (such as "
I frames
" in
MPEG-2
) are not allowed to copy data from other frames, so they require much more data than other frames nearby.
[51]
It is possible to build a computer-based video editor that spots problems caused when I frames are edited out while other frames need them. This has allowed newer formats like
HDV
to be used for editing. However, this process demands a lot more computing power than editing intraframe compressed video with the same picture quality. But, this compression is not very effective to use for any audio format.
[52]
Profiles and levels
[
edit
]
A video coding format can define optional restrictions to encoded video, called
profiles
and levels. It is possible to have a decoder which only supports decoding a subset of profiles and levels of a given video format, for example to make the decoder program/hardware smaller, simpler, or faster.
[53]
A
profile
restricts which encoding techniques are allowed. For example, the H.264 format includes the profiles
baseline
,
main
and
high
(and others). While
P-slices
(which can be predicted based on preceding slices) are supported in all profiles,
B-slices
(which can be predicted based on both preceding and following slices) are supported in the
main
and
high
profiles but not in
baseline
.
[54]
A
level
is a restriction on parameters such as maximum resolution and data rates.
[54]
See also
[
edit
]
Notes
[
edit
]
References
[
edit
]
- ^
Thomas Wiegand
; Gary J. Sullivan; Gisle Bjontegaard & Ajay Luthra (July 2003).
"Overview of the H.264 / AVC Video Coding Standard"
(PDF)
. IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY.
- ^
a
b
"SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS : Infrastructure of audiovisual services ? Coding of moving video : Advanced video coding for generic audiovisual services"
. Itu.int
. Retrieved
January 6,
2015
.
- ^
"Front Page"
. Alliance for Open Media
. Retrieved
May 23,
2016
.
- ^
Adrian Grange; Peter de Rivaz & Jonathan Hunt.
"VP9 Bitstream & Decoding Process Specification"
(PDF)
.
- ^
"Audio/Video"
. The Chromium Projects
. Retrieved
May 23,
2016
.
- ^
"Media formats supported by the HTML audio and video elements"
. Mozilla
. Retrieved
May 23,
2016
.
- ^
Rowan Trollope (October 30, 2013).
"Open-Sourced H.264 Removes Barriers to WebRTC"
. Cisco. Archived from
the original
on May 14, 2019
. Retrieved
May 23,
2016
.
- ^
"Chapter 3 : Modified A* Prune Algorithm for finding K-MCSP in video compression"
(PDF)
. Shodhganga.inflibnet.ac.in
. Retrieved
January 6,
2015
.
- ^
a
b
c
d
e
f
g
h
i
j
"History of Video Compression"
.
ITU-T
. Joint Video Team (JVT) of ISO/IEC MPEG & ITU-T VCEG (ISO/IEC JTC1/SC29/WG11 and ITU-T SG16 Q.6). July 2002. pp. 11, 24?9, 33, 40?1, 53?6
. Retrieved
November 3,
2019
.
- ^
Robinson, A. H.; Cherry, C. (1967). "Results of a prototype television bandwidth compression scheme".
Proceedings of the IEEE
.
55
(3).
IEEE
: 356?364.
doi
:
10.1109/PROC.1967.5493
.
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a
b
c
d
e
f
g
h
i
Ghanbari, Mohammed (2003).
Standard Codecs: Image Compression to Advanced Video Coding
.
Institution of Engineering and Technology
. pp. 1?2.
ISBN
9780852967102
.
- ^
a
b
c
d
e
f
Lea, William (1994).
Video on demand: Research Paper 94/68
.
House of Commons Library
. Retrieved
September 20,
2019
.
- ^
Lee, Jack (2005).
Scalable Continuous Media Streaming Systems: Architecture, Design, Analysis and Implementation
.
John Wiley & Sons
. p. 25.
ISBN
9780470857649
.
- ^
Ahmed, Nasir
(January 1991).
"How I Came Up With the Discrete Cosine Transform"
.
Digital Signal Processing
.
1
(1): 4?5.
doi
:
10.1016/1051-2004(91)90086-Z
.
- ^
Ahmed, Nasir
; Natarajan, T.; Rao, K. R. (January 1974), "Discrete Cosine Transform",
IEEE Transactions on Computers
,
C-23
(1): 90?93,
doi
:
10.1109/T-C.1974.223784
,
S2CID
149806273
- ^
Rao, K. R.
; Yip, P. (1990),
Discrete Cosine Transform: Algorithms, Advantages, Applications
, Boston: Academic Press,
ISBN
978-0-12-580203-1
- ^
a
b
Habibi, Ali (1974). "Hybrid Coding of Pictorial Data".
IEEE Transactions on Communications
.
22
(5): 614?624.
doi
:
10.1109/TCOM.1974.1092258
.
- ^
Chen, Z.; He, T.; Jin, X.; Wu, F. (2019). "Learning for Video Compression".
IEEE Transactions on Circuits and Systems for Video Technology
.
30
(2): 566?576.
arXiv
:
1804.09869
.
doi
:
10.1109/TCSVT.2019.2892608
.
S2CID
13743007
.
- ^
Pratt, William K. (1984).
Advances in Electronics and Electron Physics: Supplement
.
Academic Press
. p. 158.
ISBN
9780120145720
.
A significant advance in image coding methodology occurred with the introduction of the concept of hybrid transform/DPCM coding (Habibi, 1974).
- ^
Ohm, Jens-Rainer (2015).
Multimedia Signal Coding and Transmission
. Springer. p. 364.
ISBN
9783662466919
.
- ^
a
b
Roese, John A.; Robinson, Guner S. (October 30, 1975). Tescher, Andrew G. (ed.). "Combined Spatial And Temporal Coding Of Digital Image Sequences".
Efficient Transmission of Pictorial Information
.
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.
doi
:
10.1117/12.965361
.
S2CID
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.
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Huang, T. S. (1981).
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.
Springer Science & Business Media
. p. 29.
ISBN
9783642870378
.
- ^
a
b
c
Stankovi?, Radomir S.; Astola, Jaakko T. (2012).
"Reminiscences of the Early Work in DCT: Interview with K.R. Rao"
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