MP4ReadSampleFromEditTime(3)

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

6       MP4ReadSampleFromEditTime  -  Read  a track sample based on a specified
7       edit list time
8

SYNTAX

10       #include <mp4.h>
11
12       bool MP4ReadSampleFromEditTime(
13            MP4FileHandle hFile,
14            MP4TrackId trackId,
15            MP4Timestamp editWhen,
16            u_int8_t** ppBytes,
17            u_int32_t* pNumBytes,
18            MP4Timestamp* pStartTime = NULL,
19            MP4Duration* pDuration = NULL,
20            MP4Duration* pRenderingOffset = NULL,
21            bool pIsSyncSample = NULL
22       );
23

ARGUMENTS

25       hFile  Specifies the mp4 file to which the operation applies.
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27       trackId
28              Specifies the track to which the operation applies.
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30       editWhen
31              Specifies which sample is to be read based on a time in the edit
32              list timeline. See MP4GetSampleIdFromEditTime() for details.
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34       ppBytes
35              Pointer  to  the pointer to the sample data. See DESCRIPTION for
36              details on this argument.
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38       pNumBytes
39              Pointer to variable that will be hold the size in bytes  of  the
40              sample.
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42       pStartTime
43              If  non-NULL, pointer to variable that will receive the starting
44              timestamp for this sample. Caveat: The timestamp is in the track
45              timescale.
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47       pDuration
48              If  non-NULL, pointer to variable that will receive the duration
49              for this sample. Caveat: The duration is in the track  timescale
50              units.
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52       pRenderingOffset
53              If non-NULL, pointer to variable that will receive the rendering
54              offset for this sample. Currently the only media type that needs
55              this  feature  is MPEG video. Caveat: The offset is in the track
56              timescale units.
57
58       pIsSyncSample
59              If non-NULL, pointer to variable that will receive the state  of
60              the sync/random access flag for this sample.
61

RETURN VALUES

63       Upon success, true (1). Upon an error, false (0).
64

DESCRIPTION

66       MP4ReadSampleFromEditTime reads the sample corresponding to the time on
67       the track edit list timeline from the specified track.  Typically  this
68       sample  is then decoded in a codec dependent fashion and rendered in an
69       appropriate fashion.
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71       The argument, ppBytes, allows for two possible approaches  for  buffer‐
72       ing:
73
74       If  the  calling  application wishes to handle its own buffering it can
75       set *ppBytes to the buffer it wishes to use. The calling application is
76       responsible  for  ensuring  that the buffer is large enough to hold the
77       sample. This can be done by using either MP4GetSampleSize() or  MP4Get‐
78       TrackMaxSampleSize()  to  determine before-hand how large the receiving
79       buffer must be.
80
81       If the value of *ppBytes is NULL, then an appropriately sized buffer is
82       automatically  malloc'ed  for  the sample data and *ppBytes set to this
83       pointer. The calling application is responsible for free'ing this  mem‐
84       ory.
85
86       The  last  four  arguments  are  pointers to variables that can receive
87       optional sample information.
88
89       Typically for audio none of these are needed. MPEG audio such as MP3 or
90       AAC  has  a  fixed  sample duration and every sample can be accessed at
91       random.
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93       For video, all of these optional values could be needed. MPEG video can
94       be encoded at a variable frame rate, with only occasional random access
95       points, and with "B frames" which cause the rendering  (display)  order
96       of the video frames to differ from the storage/decoding order.
97
98       Other media types fall between these two extremes.
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NAME

SYNTAX

ARGUMENTS

RETURN VALUES

DESCRIPTION

SEE ALSO