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>14.3. Flow of data between elements and time</A
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> Now we will see how time information travels the pipeline in different states.
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> The pipeline starts playing.
The source element typically knows the time of each sample.
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>
First, the source element sends a newsegment event. This event carries information
about the current relative time of the next sample. This relative time is
arbitrary, but it must be consistent with the timestamp that will be
placed in buffers. It is expected to be the relative time to the start
of the media stream, or whatever makes sense in the case of each media.
When receiving it, the other elements adjust their offset of the element time so that this
time matches the time written in the event.
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> Then the source element sends media samples in buffers. This element places a
timestamp in each buffer saying when the sample should be played. When the
buffer reaches the sink pad of the last element, this element compares the
current element time with the timestamp of the buffer. If the timestamp is
higher or equal it plays the buffer, otherwise it waits until the time to
place the buffer arrives with <CODE
CLASS="function"
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> If the stream is seeked, the next samples sent will have a timestamp that
is not adjusted with the element time. Therefore, the source element must
send a newsegment event.
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> Sometimes it
is a parser element the one that knows the time, for instance if a pipeline
contains a filesrc element connected to a MPEG decoder element, the former
is the one that knows the time of each sample, because the knowledge of
when to play each sample is embedded in the MPEG format. In this case this
element will be regarded as the source element for this discussion.
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