When comparing the performance of MPEG standards such as MPEG-4 and H.264, it is important to note that results may vary between encoders that use the same standard. This is because the designer of an encoder can choose to implement different sets of tools defined by a standard. As long as the output of an encoder conforms to a standard’s format and decoder, it is possible to make different implementations. An MPEG standard, therefore, cannot guarantee a given bit rate or quality, and comparisons cannot be properly made without first defining how the standards are implemented in an encoder. A decoder, unlike an encoder, must implement all the required parts of a standard in order to decode a compliant bit stream. A standard specifies exactly how a decompression algorithm should restore every bit of a compressed video.
The graph on the following page provides a bit rate comparison, given the same level of image quality, among the following video standards: Motion JPEG, MPEG-4 Part 2 (no motion compensation), MPEG-4 Part 2 (with motion compensation) and H.264 (baseline profile).
|Axis’ H.264 encoder generated up to 50% fewer bits per second for a sample video sequence than an MPEG-4 encoder with motion compensation. The H.264 encoder was at least three times more efficient than an MPEG-4 encoder with no motion compensation and at least six times more efficient than with Motion JPEG.|
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