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design: add some ideas for SKIP mode trickmodes

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This commit is contained in:
Wim Taymans 2009-10-27 15:47:39 +01:00
parent 03baa04059
commit ac1e923617
1 changed files with 13 additions and 6 deletions
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19
docs/design/part-trickmodes.txt
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@ -136,18 +136,22 @@ client side forward trickmodes
The seek happens as stated above. a NEW_SEGMENT event is sent downstream with a rate The seek happens as stated above. a NEW_SEGMENT event is sent downstream with a rate
different from 1.0. Plugins receiving the NEW_SEGMENT can decide to perform the different from 1.0. Plugins receiving the NEW_SEGMENT can decide to perform the
rate conversion of the media data (retimestamp video frames, resample audio, ...). rate conversion of the media data (retimestamp video frames, resample audio, ...).
A plugin should not drop frames unless the SKIP flag is set. When the SKIP flag is
set, a plugin can decide to drop frames in the case of fast playback or use a more If a plugin decides to resample or retimestamp, it should modify the NEW_SEGMENT with
efficient decoding algorithm (skip B frames, ...). If a plugin decides to resample a rate of 1.0 and update the applied rate so that downstream elements don't resample
or retimestamp, it should modify the NEW_SEGMENT with a rate of 1.0 and update the again but are aware that the media has been modified.
applied rate so that downstream elements don't resample again but are aware that the
media has been modified.
The GStreamer base audio and video sinks will resample automatically if they receive The GStreamer base audio and video sinks will resample automatically if they receive
a NEW_SEGMENT event with a rate different from 1.0. The position reporting in the a NEW_SEGMENT event with a rate different from 1.0. The position reporting in the
base audio and video sinks will also depend on the applied rate of the segment base audio and video sinks will also depend on the applied rate of the segment
information. information.
When the SKIP flag is set, frames can be dropped in the elements. If S is the
speedup factor, a good algorithm for implementing frame skipping is to send audio in
chunks of Nms (usualy 300ms is good) and then skip ((S-1) * Nns) of audio data.
For the video we send only the keyframes in the (S * Nns) interval. In this
case, the demuxer would scale the timestamps and would set an applied rate of S.
client side backwards trickmode client side backwards trickmode
------------------------------- -------------------------------
@ -195,6 +199,9 @@ For plugins the following rules apply:
be added to the applied_rate and subtracted from the rate members in the be added to the applied_rate and subtracted from the rate members in the
NEWSEGMENT event. NEWSEGMENT event.
In SKIP mode, the same algorithm as for forward SKIP mode can be used.
Notes: Notes:
- The clock/running_time keeps running forward. - The clock/running_time keeps running forward.