EXFO EXpert IPTV Test Tools (FTB-1 / 2 Pro) - Manual (Page 53)

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In Figure 2-6, the sequence was encoded at a bitrate of 1127Kbps (138KB/s). The use of
coarser quantization conserves bandwidth, but creates distortion that impairs overall image
quality throughout the entire video sequence.
A.1.2.2 Performance of Video Coders
There are many standardized video coding algorithms, such as ITU-T H.261, H.263, H.264,
ISO/IEC MPEG-1, MPEG-2 and MPEG-4, AVS, VC-1, etc. These standards do not explicitly define
codecs; they only define the syntax of an encoded video bitstream together with the methods
of decoding the bitstream. The consequence is that there might be significant quality
differences between codecs conforming to the same standard [16]. The Windows Media 9
(VC-1) of Microsoft and RealVideo of RealNetworks are widely used proprietary video coding
algorithms for video streaming applications.
As a rule of thumb, ITU-T H.263 reduces the coding bitrate by about 50% against H.261 for
comparable video quality. ITU-T H.264/AVC significantly outperforms all other listed
standards. Average bit-savings of more than 60% relative to MPEG-2 are reported. H.264/AVC
Main Profile provides more than 1/3 bitrate saving relative to its competitors, MPEG-4
Advanced Simple Profile (ASP) and H.263 Conversational High Compression (CHC) Profiles [25].
Reports show that WMV 9 (VC-1) achieved similar quality to MPEG-2 and MPEG-4 with
only1/3
and 1/2 of the bitrate, respectively [21]. A paper by Bennet and Bock [13] concludes that
comparing H.264/AVC and VC-1, there is very little performance difference between them.
A.1.2.3 Effective Coding Bitrate
The bitrate used in estimating the mean squared error as referenced in the beginning of
section 2.2.1 can be adjusted to an effective bitrate based on performance of a video codec
described above . The effective bitrate also needs to be adjusted based on the frame
resolution and frame rate of the video signal. Videoconferencing applications generally
support low to medium bitrates and frame resolution. The most commonly used resolutions
are QCIF (176x144) and CIF (352x288) at 10 to 30 frames per second. Entertainment-quality