macroblock. Video profiles and levels MPEG-2 video supports a wide range of applications from mobile to high quality HD editing. For many applications, it is unrealistic and too expensive to support the entire standard. To allow such applications to support only subsets of it, the standard defines profiles and levels. A profile defines sets of features such as B-pictures, 3D video, chroma format, etc. The level limits the memory and processing power needed, defining maximum bit rates, frame sizes, and frame rates. A MPEG application then specifies the capabilities in terms of profile and level. For example, a DVD player may say it supports up to main profile and main level (often written as MP@ML). It means the player can play back any MPEG stream encoded as MP@ML or less. The tables below summarizes the limitations of each profile and level, though there are constraints not listed here. Note that not all profile and level combinations are permissible, and scalable modes modify the level restrictions. A few common MPEG-2 Profile/Level combinations are presented below, with particular maximum limits noted: Applications Some applications are listed below. DVD-Video - a standard definition consumer video format. Uses 4:2:0 color subsampling and variable video data rate up to 9.8 Mbit/s. MPEG IMX - a standard definition professional video recording format. Uses intraframe compression, 4:2:2 color subsampling and user-selectable constant video data rate of 30, 40 or 50 Mbit/s. HDV - a tape-based high definition video recording format. Uses 4:2:0 color subsampling and 19.4 or 25 Mbit/s total data rate. XDCAM - a family of tapeless video recording formats, which, in particular, includes formats based on MPEG-2 Part 2. These are: standard definition MPEG IMX (see above), high definition MPEG HD, high definition MPEG HD422. MPEG IMX and MPEG HD422 employ 4:2:2 color subsampling, MPEG HD employs 4:2:0 color subsampling. Most subformats use selectable constant video data rate from 25 to 50 Mbit/s, although there is also a variable bitrate mode with maximum 18 Mbit/s data rate. XF Codec - a professional tapeless video recording format, similar to MPEG HD and MPEG HD422 but stored in a different container file. HD DVD - defunct high definition consumer video format. Blu-ray Disc - high definition consumer video format. Broadcast TV - in some countries MPEG-2 Part 2 is used for digital broadcast in high definition. For example, ATSC specifies both several scanning formats (480i, 480p, 720p,