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Update some docs regarding reverse playback.

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Original commit message from CVS:
* docs/design/part-trickmodes.txt:
* gst/gstevent.c:
Update some docs regarding reverse playback.
This commit is contained in:
Wim Taymans 2006-10-16 11:46:04 +00:00
parent 12edfe0b9c
commit 42d34f86ba
3 changed files with 39 additions and 15 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2006-10-16 Wim Taymans <wim@fluendo.com>
* docs/design/part-trickmodes.txt:
* gst/gstevent.c:
Update some docs regarding reverse playback.
2006-10-15 Tim-Philipp Müller <tim at centricular dot net>
Patch by: Marcus Granado <mrc dot gran at gmail com>

41
docs/design/part-trickmodes.txt
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@ -160,27 +160,42 @@ For backwards playback the following rules apply:
For plugins the following rules apply:
- A source plugin sends data in chunks starting from the last chunk of the file.
The actual bytes are not reversed.
- A source plugin sends data in chunks starting from the last chunk of the
file. The actual bytes are not reversed. Each chunk that is not forward
continuous with the previous chunk is marked with a DISCONT flag.
- A demuxer accumulates the chunks. As soon as a keyframe is found, everything
starting from the keyframe up to the accumulated data is sent downstream.
Timestamps on the buffers are set starting from the stop position to start,
effectively going backwards.
effectively going backwards. Chunks are marked with DISCONT when they are not
forward continuous with the previous buffer.
- A decoder decodes and accumulates all frames. If a new keyframe or EOS is received,
all accumulated frames are sent downsteam in reverse.
- A video decoder decodes and accumulates all decoded frames. If a buffer with
a DISCONT, accumulate NEWSEGMENT or EOS is received, all accumulated frames
are sent downsteam in reverse.
- A sink reverses (for audio) and retimestamps (audio, video) the buffers before
playing them back. Retimestamping occurs relative to the stop position, making
the timestamps increase again and suitable for synchronizing against the clock.
- An audio decoder decodes and accumulates all decoded audio. If a buffer with
a DISCONT, accumulate NEWSEGMENT or EOS is received, all accumulated audio
is sent downstream in reverse order. Some audio codecs need the previous
data buffer to decode the current one, in that case, the previous DISCONT
buffer needs to be combined with the last non-DISCONT buffer to generate the
last bit of output.
- for transcoding, audio and video resamplers can be used to reverse, resample and
retimestamp the buffers.
- A sink reverses (for audio) and retimestamps (audio, video) the buffers
before playing them back. Retimestamping occurs relative to the stop
position, making the timestamps increase again and suitable for synchronizing
against the clock.
Audio sinks also have to perform simple resampling before playing the
samples.
- for transcoding, audio and video resamplers can be used to reverse, resample
and retimestamp the buffers. Any rate adjustments performed on the media must
be added to the applied_rate and subtracted from the rate members in the
NEWSEGMENT event.
Notes:
- The clock keeps running forward.
- backwards playback potentially uses a lot of memory as frames and undecoded data
gets buffered.
- The clock/stream_time keeps running forward.
- backwards playback potentially uses a lot of memory as frames and undecoded
data gets buffered.

7
gst/gstevent.c
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@ -811,8 +811,11 @@ gst_event_parse_qos (GstEvent * event, gdouble * proportion,
* that the position should not be updated.
*
* When the rate is positive and @start has been updated, playback will start
* from the newly configured start position. For negative rates, playback will
* start from the newly configured stop position.
* from the newly configured start position.
*
* For negative rates, playback will start from the newly configured stop
* position (if any). If the stop position if updated, it must be different from
* -1 for negative rates.
*
* It is not possible to seek relative to the current playback position, to do
* this, PAUSE the pipeline, query the current playback position with