Conversion of Time Values between SMPTE ST 12-1 Time Code, MPEG-2 PCR Time Base and Absolute Time

Published by	Publication Date	Number of Pages
SMPTE	07/29/2016		20

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Category: SMPTE

Description

SMPTE EG 40 – Conversion of Time Values between SMPTE ST 12-1 Time Code, MPEG-2 PCR Time Base and Absolute Time

This guideline specifies a set of formulas for converting between “SMPTE 12M time code” (correctly SMPTE ST 12-1 time code), MPEG-2 systems layer program clock reference (PCR) time base, and local wall clock time. Included are formulas for converting SMPTE ST 12-1 time address values and MPEG-2 PCR time base values to local wall clock time, and formulas for converting SMPTE ST 12-1 time address values directly to/from MPEG-2 PCR time base values. Local wall clock time conversion formulas are useful for converting between different frame rates of SMPTE ST 12-1 time code; e.g., a 24-fps SMPTE time code running at 23.976 fps could be converted to true time and then to a 29.97 drop frame SMPTE time code value. Finally, a discussion of how ST 12-1 time code may be carried within the coded video structures of both MPEG-2 and MPEG-4 AVC is provided.