1MP4(3)                      MP4 File Format Library                     MP4(3)
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NAME

6       MP4GetSampleRenderingOffset  - Get the rendering offset of a track sam‐
7       ple
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SYNTAX

10       #include <mp4.h>
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12       MP4Duration MP4GetSampleRenderingOffset(
13            MP4FileHandle hFile,
14            MP4TrackId trackId,
15            MP4SampleId sampleId
16       );
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ARGUMENTS

19       hFile  Specifies the mp4 file to which the operation applies.
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21       trackId
22              Specifies the track to which the operation applies.
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24       sampleId
25              Specifies the sample to which the operation applies. Caveat: the
26              first sample has id 1 not 0.
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RETURN VALUES

30       Upon  success,  the rendering offset in track time scale units. Upon an
31       error, MP4_INVALID_DURATION.
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DESCRIPTION

34       MP4GetSampleRenderingOffset returns the rendering offset of the  speci‐
35       fied sample from the specified track in the track time scale units. See
36       MP4ConvertFromTrackDuration() for how to map this value to another time
37       scale.
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39       The sample rendering offset is typically zero for all media types other
40       than video. For video, encodings such as those  defined  by  MPEG  have
41       three  types  of  frames:  I, P, and B. To increase coding efficiency B
42       frames can depend on I or P frames that should be rendered after the  B
43       frame. However to decode the B frame the I or P frame must already have
44       been decoded. This situation is addressed  by  placing  the  frames  in
45       decoding  order in the video track, and then setting the rendering off‐
46       set property to indicate when the video frame should actually  be  ren‐
47       dered to the screen. Hence the start time of a sample indicates when it
48       should be decoded, the start time plus the rendering  offset  indicates
49       when it should be rendered.
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SEE ALSO

52       MP4(3) MP4ConvertFromTrackDuration(3)
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56Cisco Systems Inc.                Version 0.9                           MP4(3)
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