Back to table of contents
The MPEG 2 specification (ISO 13818) was designed for broadcast TV and others using interlaced images. It gives higher picture quality than MPEG 1 but using a higher data rate. At lower bit rates, there is no point in using MPEG 2 over MPEG 1. At bit rates above 4 Mbits/s MPEG 2 should be used instead of MPEG 1. Unlike MPEG 1, MPEG 2 supports interlaced TV systems and Vertical Blanking Interval signals.
MPEG 2 also includes higher audio quality and can use surround sound with 5.1 channels. You can also use a variable video bit rate (VBR) for the audio. Broadcast applications, currently using MPEG-2, generally use around 7 Mb/s fixed data rate.
MPEG 2 uses the same frame types as MPEG 1 except that each frame comprises two interlaced fields. Also each group of pictures (GOP) is 15 (PAL) or 18 (NTSC) frames in length.
I B P B P B P ie there is only one B-frame between P-frames instead of two for MPEG 1.
As Stored on Disk
Each macroblock of a B-frame is coded as a change from the previous or next P-frame or I-frame. The I-frames are repeated at approximately 0.5 second intervals, otherwise the PBPBP.. pattern is repeated indefinitely.