Quicktime File Format (2012-08-14).pdf

Some Useful Examples and ScenariosCreating a Timecode Track for 29.97 FPS VideoCreating a Timecode Track for 29.97 FPS VideoA timecode track specifies timecode information for other tracks. The timecode keeps track of the time codesof the original source of the video and audio. After a movie has been edited, the timecode can be extractedto determine the source tape and the time codes of the frames.It is important that the timecode track have the same time scale as the video track. Otherwise, the timecodewill not tick at the exact same time as the video track.For each contiguous source tape segment, there is a single timecode sample that specifies the timecode valuecorresponding to the start of the segment. From this sample, the timecode value can be determined for anypoint in the segment.The sample description for a timecode track specifies the timecode system being used (for example, a 30-fpsdrop frame) and the source information. Each sample is a timecode value.Since the timecode media handler is a derived from the base media handler, the media information atom startswith a generic media header atom. The timecode atoms would contain the following data values:Atom sizeAtom type77'gmhd'Atom sizeAtom typeVersion/FlagsGraphics modeOpcolor (red)Opcolor (green)Opcolor (blue)BalanceReservedAtom sizeAtom type69'gmin'00x00400x80000x80000x80000045'tmcd'Atom size372012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.352