Basic Concepts
SMPTE timecodes ( /ˈsɪmtiː/) contain binary coded decimal hour:minute:second:frame identification and 32 bits for use by users. There are also drop-frame and color framing flags and three extra 'binary group flag' bits used for defining the use of the user bits. The formats of other varieties of SMPTE time codes are derived from that of the longitudinal timecode.
Time codes may use a number of frame rates. Common ones are:
- 24 frame/sec (film, ATSC, 2k, 4k, 6k)
- 25 frame/sec (PAL (Europe, Uruguay, Argentina, Australia), SECAM, DVB, ATSC)
- 29.97 (30 ÷ 1.001) frame/sec (NTSC American System (US, Canada, Mexico, Colombia, etc.), ATSC, PAL-M (Brazil))
- 30 frame/sec (ATSC)
In general, SMPTE timecode frame rate information is implicit, known from the rate of arrival of the timecode from the medium, or other metadata encoded in the medium. The interpretation of several bits, including the "colour framing" and "drop frame" bits, depends on the underlying data rate. In particular, the drop frame bit is only valid for a nominal frame rate of 30 frame/s: see below for details.
More complex timecodes such as vertical interval timecode can also include extra information in a variety of encodings.
Read more about this topic: SMPTE Timecode
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