H.262[2] or MPEG-2 Part 2 (formally known as ITU-T Recommendation H.262 and ISO/IEC 13818-2,[3] also known as MPEG-2 Video) is a video coding format standardised and jointly maintained by ITU-T Study Group 16 Video Coding Experts Group (VCEG) and ISO/IEC Moving Picture Experts Group (MPEG), and developed with the involvement of many companies.
Video compression is practical because the data in pictures is often redundant in space and time.
Also, because of the way the eye works, it is possible to delete or approximate some data from video pictures with little or no noticeable degradation in image quality.
Another common practice to reduce the amount of data to be processed is to subsample the two chroma planes (after low-pass filtering to avoid aliasing).
While the discussion below in this section generally describes MPEG-2 video compression, there are many details that are not discussed, including details involving fields, chrominance formats, responses to scene changes, special codes that label the parts of the bitstream, and other pieces of information.
The coding of an I-frame takes advantage of spatial redundancy and of the inability of the eye to detect certain changes in the image.
The conversion from 8-bit integers to real-valued transform coefficients actually expands the amount of data used at this stage of the processing, but the advantage of the transformation is that the image data can then be approximated by quantizing the coefficients.
Many of the transform coefficients, usually the higher frequency components, will be zero after the quantization, which is basically a rounding operation.
P-frames and B-frames might follow an I-frame like this, IBBPBBPBBPBB(I), to form a Group of Pictures (GOP); however, the standard is flexible about this.
The encoder selects which pictures are coded as I-, P-, and B-frames.
To generate a P-frame, the previous reference frame is reconstructed, just as it would be in a TV receiver or DVD player.
This "residual" is appended to the motion vector and the result sent to the receiver or stored on the DVD for each macroblock being compressed.
MPEG-2 video supports a wide range of applications from mobile to high quality HD editing.
A profile defines sets of features such as B-pictures, 3D video, chroma format, etc.
It means the player can play back any MPEG stream encoded as MP@ML or less.
A few common MPEG-2 Profile/Level combinations are presented below, with particular maximum limits noted: Some applications are listed below.
The following organizations have held patents for MPEG-2 video technology, as listed at MPEG LA.