Background of H.264 standardization
H.264 development was started in 1998 as a long term project of ITU-T, and its target was to achieve half the bit-rate of the H.263 and MPEG-4 standards, for the same perceived video quality. Unlike past video compression standards (MPEG-1/-2/-4, H.261/262/263), the H.264 effort was to improve compression efficiency and not restrict the implementation complexity. This resulted in the current H.264 implementation that requires substantial amount of computational power. The resulting H.264 encoder offers improved features in which the encoder structure and compression profiles are quite different from MPEG-2.
H.264 Encoder Structure
This diagram indicates a generalized hybrid (motion-compensation and transform) H.264 encoder structure which is common to MPEG-2 and H.264 encoders; however the details in each box in the block diagram are different between Codecs. Table-2 shows the differences from MPEG-2 for those items which improve video quality significantly.
Table-2 H.264 Encoder Improvements Versus MPEG-2 Encoder
Table-3 lists the various profiles offered in the H.264 standard, along with a brief description, as well as target applications.
Table-3 H.264 Application Oriented Profiles
The first four profiles (Baseline, Main, Extended, High) are intended for consumer applications, while the following three profiles (High 10, High 4:2:2, High 4:4:4) are intended for non-consumer (professional) applications. There are also "Level" definitions that are similar to MPEG-2. Level-3 is for SD (standard definition: 720x480x30 or 720x576x25), and Level-4 is for HD (high definition: 1920x1080x30 or x25).
