[Bug 692397] New: New plugin for MPEG TS time shifting

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=692397
  GStreamer | gst-plugins-bad | git

           Summary: New plugin for MPEG TS time shifting
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: krzysztof.konopko at youview.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


Created an attachment (id=234220)
 View: https://bugzilla.gnome.org/attachment.cgi?id=234220
 Review: https://bugzilla.gnome.org/review?bug=692397&attachment=234220

Proposed implementation

tstimeshift: New plugin for MPEG TS time shifting

This is an initial proposal.  I'd like to ask for any help, views, suggestions
and directions.

The plugin is base on Fluendo timeshift element [1] although quite
substantially changed.  The proposed code is maintained on GitHub [2].  The
gsttstimeshift comprises several elements that can be used for MPEG TS time
shifting:

  tsshifter    : Time Shift for MPEG TS streams
  tsshifterbin : Time Shift + TS parser for MPEG TS streams
  tsseeker     : Time Shift seeker
  tsindexer    : Indexer for MPEG-TS streams

A typical pipeline that makes use of them would look like:
  <some MPEG TS src> ! tsshifterbin ! <some MPEG TS sink>

The tsshifterbin element will instantiate elements as follows:

  tsparse ! tsindexer ! tsshifter ! tsseeker

and prepare tsindexer ("tune" it to look for the right PID containing PCRs).

Potentially tsshifter can be replaced with queue2 (see the problems below) and
this is actually one of the goals.

Problems still to be considered/solved/improved:
---------------------------------------
- naming
  Both tsindexer and tsseeker are supposed to be MPEG TS agnostic but ATM they
are TS specific, hence their names.
  Also the tsshifter is actually a ring buffer.

- tsindexer
  * uses overengineered for this use case and abandoned GstIndex API (local
copy)
    * can't remove index entries
    * can't write the index to the disk
  * duplicates parsing TS packets logic from tsparse
    tsparse would have to be improved to send some additional timestamp
information (e. g. as tags or as buffer timestamps) so that the indexer could
pick them up. The indexer itself could be a generic component (no knowledge
about TS packets), hard to come up with the right format though.

- tsindexer and tsseeker share an index object while it should be shared
through some index database

- tsshifter
  * it's actually a ring buffer, not a shifter (see naming notes above)
  * ideally it should be replaced with queue2
    * as a first attempt, replacement could be optional (both tsshifter and
queue2 co-exist)
      There are still some issues when using queue2 instead of tsshifter that
have to be solved.
    * as a goal tsshifter could be completely replaced with queue2 which might
require some changes/improvements of the latter:
      * custom allocator can be used (see FileMemAllocator:
https://bugzilla.gnome.org/show_bug.cgi?id=691299)

- tests still to be written
- documentation

[1] https://github.com/kkonopko/gst-fluendo-timeshift
[2] https://github.com/kkonopko/gst-plugins-bad/tree/ts-timeshifter-element

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