itstream can be in one of two formats: the NAL unit stream format or the byte stream format. The NAL unit stream format is conceptually the more "basic" type. It consists of a sequence of syntax structures called NAL units. This sequence is ordered in decoding order. There are constraints imposed on the decoding order (and contents) of the NAL units in the NAL unit stream. The byte stream format can be constructed from the NAL unit stream format by ordering the NAL units in decoding order and prefixing each NAL unit with a start code prefix and zero or more zero-valued bytes to form a stream of bytes. The NAL unit stream format can be extracted from the byte stream format by searching for the location of the unique start code prefix pattern within this stream of bytes. Methods of framing the NAL units in a manner other than use of the byte stream format are outside the scope of this Recommendation | International Standard. The byte stream format is specified in Annex B. Source, decoded, and output picture formats This clause specifies the relationship between source and decoded frames and fields that is given via the bitstream. The video source that is represented by the bitstream is a sequence of either or both frames or fields (called collectively pictures) in decoding order. The source and decoded pictures (frames or fields) are each comprised of one or more sample arrays: Luma (Y) only (monochrome), with or without an auxiliary array. Luma and two Chroma (YCbCr or YCgCo), with or without an auxiliary array. Green, Blue and Red (GBR, also known as RGB), with or without an auxiliary array. Arrays representing other unspecified monochrome or tri-stimulus colour samplings (for example, YZX, also known as XYZ), with or without an auxiliary array. Rec. ITU-T H.264 (01/2012) For convenience of notation and terminology in this Specification, the variables and terms associated with these arrays are referred to as luma (or L or Y) and chroma, where the two chroma arrays are referred to as Cb and Cr; regardless of the a