mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-18 07:47:17 +00:00
133 lines
3.4 KiB
Text
133 lines
3.4 KiB
Text
1) intro
|
|
--------
|
|
|
|
For efficient and accurate seeking, a plugin typically needs
|
|
an index of possible seek positions (in time, bytes, samples, ...).
|
|
|
|
The purpose of GstTimecache is to provide an infrastructure for
|
|
plugins to maintain such an index.
|
|
|
|
By creating a generic interface to this functionality, it is also
|
|
possible for the application to make use of the generated index.
|
|
possible use cases are: saving/loading of indexes, obtain an
|
|
overview of the indexed stream (where is sample N, where is
|
|
the keyframe...)
|
|
|
|
|
|
This document describes a proposed API for this functionality.
|
|
|
|
|
|
2) Requirements
|
|
---------------
|
|
|
|
Bare minimum:
|
|
|
|
- store mappings between format1 and format2 (bytes<->time,
|
|
samples<->tracks, ...)
|
|
- update the mappings (add/remove/change entries)
|
|
- query the index, locate entries.
|
|
- store arbitrary extra metadata in the timecache (media file,
|
|
time, author, ...)
|
|
- set/get cache on elements.
|
|
|
|
Nice to have:
|
|
|
|
- cache groups with varying certainty that are merged.
|
|
- API to control the indexing process, what gets indexed, how much,
|
|
...)
|
|
- Get notification when a new entry is added, together with an
|
|
option to turn off in-memory caching, this could be used to
|
|
do direct-to-disk indexing (for large files) insteda of to-memory.
|
|
|
|
3) use cases
|
|
------------
|
|
|
|
a) indexing an mpeg systems stream
|
|
|
|
- create an empty timecache object
|
|
- create filesrc ! mpegparse
|
|
- set timecache on mpegparse
|
|
- run the pipeline to EOS
|
|
- mpegparse will create a mapping from SCR to byte offset
|
|
and add it to the cache.
|
|
- read/save timecache
|
|
|
|
b) running an mpeg with a previously created cache
|
|
|
|
- create timecache object from saved index
|
|
- create filesrc ! mpegparse
|
|
- set the timecache on mpegparse
|
|
- run the pipeline, seek, ...
|
|
- mpegparse uses the timecache to do accurate seek to
|
|
SCR timestamps.
|
|
|
|
c) indexing an mpeg systems stream, SCR, video and audio elementary
|
|
streams.
|
|
|
|
- create an empty timecache object
|
|
- create filesrc ! mpegdemux
|
|
- set timecache on mpegdemux
|
|
- run the pipeline to EOS
|
|
- mpegparse will create a mappings for:
|
|
* SCR to byte offset
|
|
* PTS + streamid to byte offset
|
|
and add it to the cache.
|
|
- read/save timecache
|
|
|
|
d) complete indexing of mpeg systems streams and audio/video
|
|
streams.
|
|
|
|
- create 3 empty timecaches
|
|
- create filesrc ! mpegdemux video_%02d! mpeg2dec
|
|
mpegdemux0 audio_%02d! mad
|
|
- set timecaches on mpegdemux, mpeg2dec, mad
|
|
- run pipeline to EOS
|
|
- mpegdemux creates timecache for SCR, PTS + streamid
|
|
- mpeg2dec creates timecache for frames + I/P/B id
|
|
- mad creates timecache for mpeg audio headers
|
|
- read/save timecaches
|
|
|
|
seeking in a fully indexed stream:
|
|
- seek on timestamp in mpeg2dec
|
|
- mpeg2dec locates previous I frame in cache, does
|
|
a timeseek on sinkpad
|
|
- mpegparse uses the cache to convert the timestamp
|
|
to an offset, then does a seek on offset
|
|
- filesrc seeks to offset
|
|
|
|
4) Entry types
|
|
--------------
|
|
|
|
- mapping between formats:
|
|
|
|
<padid> <flags> <format> <position>, <format> <position>, ...
|
|
|
|
- metadata, streaminfo, other objects:
|
|
|
|
<padid> <format> <position>, <keyword> gpointer
|
|
|
|
|
|
5) implementation
|
|
-----------------
|
|
|
|
We define an abstract base class GstTimeCache with following
|
|
abstract methods:
|
|
|
|
|
|
6) cache format example
|
|
-----------------------
|
|
|
|
We define a binary format for the cache for space/speed reasons.
|
|
It is entirely possible to create alternative implementations.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|