H.263 Video Coding

H.263 is a provisional ITU-T standard, it is due to be published sometime in 1995/1996. It was designed for low bitrate communication, early drafts specified datarates less than 64 Kbits/s, however this limitation has now been removed. It is expected that the standard will be used for a wide range of bitrates, not just low bitrate applications. It is expected that H.263 will replace H.261 in many applications.

The coding algorithm of H.263 is similar to that used by H.261, however with some improvements and changes to improve performance and error recovery. The differences between the H.261 and H.263 coding algorithms are listed below. Half pixel precision is used for motion compensation whereas H.261 used full pixel precision and a loop filter. Some parts of the hierarchical structure of the datastream are now optional, so the codec can be configured for a lower datarate or better error recovery. There are now four optional negotiable options included to improve performance: Unrestricted Motion Vectors, Syntax-based arithmetic coding, Advance prediction, and forward and backward frame prediction similar to MPEG called P-B frames.

H.263 supports five resolutions. In addition to QCIF and CIF that were supported by H.261 there is SQCIF, 4CIF, and 16CIF. SQCIF is approximately half the resolution of QCIF. 4CIF and 16CIF are 4 and 16 times the resolution of CIF respectively. The support of 4CIF and 16CIF means the codec could then compete with other higher bitrate video coding standards such as the MPEG standards.

Picture Formats Supported
bitrate (Mbit/s)
10 frames/s 30 frames/s
Grey Colour Grey Colour
SQCIF 128 96 Yes 1.0 1.5 3.0 4.4
QCIF 176 144 Yes Yes 2.0 3.0 6.1 9.1
CIF 352 288 Optional Optional 8.1 12.2 24.3 36.5
4CIF 704 576 Optional 32.4 48.7 97.3 146.0
16CIF 1408 1152 Optional 129.8 194.6 389.3 583.9

I have coded some example video sequences with the H.263 codec they are shown below. Also some graphs of Image quality versus bitrate and compression ratio as shown below. The Image quality measure used is the peak signal to noise ratio (PSNR). A comparison of H.263 with the H.261 video codec is also shown below.

Some Example H.263 coded Video sequences

Here are some H.263 video sequences. They can be downloaded by clicking in the table below. Two formats are available, MPEG and H.263. The MPEG sequences were generated by recoding the decoded H.263, and the quality is therefore not as good as the pure H.263. The H.263 sequences were produced using a software codec from Telenor Research. This source code is no longer available from Telenor, however an improved version in available from Univ. British Columbia: Image Processing GroupMaintainers of current version of telenor H.263 software, with H.263+ extensions.

The Telenor H.263 decoder version 1.5 is required to view the H.263 sequences, the source code can no longer be downloaded from Telenor Research. A Microsoft Windoze version is also available check their Web Site for details. Note however the windoze version probably won't work since it may use a latest version of the decoder. A compiled LINUX binary is available, see below. A MPEG player is available from Berkeley university however this also only compiles for UNIX, but DOS/Windoze versions are available.

The H.263 files are smaller than the MPEG ones, and so are faster to download. The mime-type our server uses for them is video/x-h263. To get your H.263 viewer to work within netscape compile the QCIF version and put the following line in your ~/.mailcap file.

video/x-h263; /usr/local/bin/tmndecode-QCIF -o4 -f10 -q %s
Modifying the filename of the binary as appropriate. A Statically linked version of the decoder for LINUX can be downloaded by clicking here.

Miss America (QCIF)

Description MPEG H.263 Average
Original, 30fps n/a 9124 1:1
10fps, 20Kbps 38.51 22.81 133:1
10fps, 50Kbps 41.75 56.70 54:1
10fps, 100Kbps 43.98 112.09 27:1
10fps, 500Kbps 48.38 505.61 6:1

Carphone (QCIF)

Description MPEG H.263 Average
Original, 30fps n/a 9124 1:1
10fps, 20Kbps 29.79 21.83 139:1
10fps, 50Kbps 32.82 52.76 58:1
10fps, 100Kbps 36.0 105.47 29:1
10fps, 200Kbps 44.5 522.4 6:1

Comparison of Quality Versus Bitrate/Compression-ratio

The graph below show the image quality versus bitrate for several QCIF video sequences, at 10 and 30 frames/s. Click on the graph for the full size version.

The graph below shows the same results but the image quality is plotted against the compression ratio. Again click the graph for the full size version.

A comparison of H.263 and H.261 video codecs

The graphs below show image quality versus bitrate and compression ratio, for both H.261 and H.263, using the same grey scale QCIF video sequences.

The graph below shows the image quality versus bitrate. The standard H.263 coding mode is used for the H.263 simulations at 10 and 30 frames/s. The H.261 simulations were done without motion compensation and with motion compensation and loop filtering (+MV + LF) at 10 and 30 frames/s. Click on the graph for the full size version.

The graph below is the same results plotted against compression ratio. Click on the graph for the full size version.

Other pages:
H.261 video coding
Robust video coding for mobile channels
Jürgen Streit's page on Wireless video telephony
Video Coding Links page
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1999/07/22 13:44:55