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117 lines
4.2 KiB
Text
117 lines
4.2 KiB
Text
mpegtsparse rebasing
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Rationale :
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-----------
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mpegtsparse code is more sane to handle and work with.
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We need a modular demuxer
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We need to avoid duplicating code regarding mpeg-ts in a gazillion
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elements and allow easy creatiof new elements.
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Battleplan :
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------------
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* Figure out code from mpegtsparse which would be also needed for a
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mpeg-ts demuxer (ex: packet/psi/pcr parsing).
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* Extract common code into a base mpegtsbase class.
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* Refactor mpegtsparse to subclass that base class.
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* Create a minimalistic demuxer that creates pads (based on PSI info)
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and outputs ES packets (let's say mpeg audio and video to start with)
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Potential subclasses :
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----------------------
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* MpegTSParse : Program splitter. Given an incoming multi-program
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mpeg-ts stream, it can provide request pads for each program. Each
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of those pads will contain the ts packets specific to that program.
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* TSDemux : Program demuxer. Given an incoming single or multi-program
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mpeg-ts stream, it will reconstruct the original Program Streams of
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the selected program and output them on dynamically created pads.
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* HDVSplitter : Given an incoming HDV mpeg-ts stream, it will locate
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the beginning of new scenes and output a mpeg-ts stream with the
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PAT/PMT/AUX packets properly ordered and marked with DISCONT, so
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that the following pipeline will automatically cut up a tape dump
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into individual scenes:
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filesrc ! hdvsplit ! multifilesink next-file=discont
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Code/Design common to a program-spliter and a demuxer :
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-------------------------------------------------------
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* Parsing TS packets
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* Establishing PAT/PMT mapping
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* Handling the notions of Programs/Streams
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* Seeking ?
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One proposal... would be to have the base class automatically create
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all the structures (and relationships) for the following objects:
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* Programs (from PAT/PMT, dunno if it could come from something
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else)
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* Program id
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* Streams contained in that program (with links to them)
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* Which stream contains the PCR
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* Metadata ?
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* Streams (ideally... in a table for fast access)
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* We want to be able to have stream-type specific information
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easily accessible also (like mpeg video specific data)
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* Maybe some other info ???
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The subclasses would then be able to make their own decision based
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on those objects.
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Maybe we could have some virtual methods that will be called when a
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new program is detected, a new stream is added, etc...
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It is the subclass who decides what's to do with a given packet once
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it's been parsed.
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tsparse : forward it as-is to the pad corresponding to the program
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tsdemux : forward it to the proper PS parser
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hdvsplit : ?
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Ideas to be taken into account for a proper demuxer :
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-----------------------------------------------------
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* Push-based (with inacurrate seeking)
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* Pull-based (with fast *AND* accurate seeking)
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* Modular system to add stream-type specific helper parsing
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* Doesn't have to be fully fledged, just enough to help any kind of
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seeking and scanning code.
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* ...
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Problems to figure out :
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------------------------
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* clock
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Needed for proper dvb playback. mpegtsdemux currently does internal
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clock estimation... to provide a clock with PCR estimations.
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A proper way to solve that would be to timestamp the buffers at the
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source element using the system clock, and then adjusting the PCR
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against those values. (i.e. doing the opposite of what's done in
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mpegtsdemux, but it will be more accurate since the timestamping is
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done at the source).
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Bugs that need fixing :
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-----------------------
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* Perfomance : Creation/Destruction of buffers is slow
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* => This is due to g_type_instance_create using a dogslow rwlock
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which take up to 50% of gst_adapter_take_buffer()
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=> Bugzilla #585375 (performance and contention problems)
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Code structure:
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MpegTSBase
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+--- MpegTSParse
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+--- TSDemux
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Known limitations and problems :
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--------------------------------
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* mpegtspacketizer
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* Assumes 188 bytes packets. It should support all modes.
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* offset/timestamp of incoming buffers need to be carried on to the
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sub-buffers in order for several demuxer features to work correctly.
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* mpegtsparser
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* SERIOUS room for improvement performance-wise (see callgrind)
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