[Bug 708532] tsdemux: skips too much when scanning for last PCR

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=708532
  GStreamer | gst-plugins-bad | git

--- Comment #4 from Edward Hervey <bilboed at bilboed.com> 2014-07-09 08:17:52 UTC ---
Created an attachment (id=280211)
 View: https://bugzilla.gnome.org/attachment.cgi?id=280211
 Review: https://bugzilla.gnome.org/review?bug=708532&attachment=280211

mpegtbase: Improve last PCR detection

When dealing with random-access content (such as files), we initially
search for the last PCR in order to figure out duration and to handle
other position estimation such as those used in seeking.

Previously, the code looking for that last PCR would search in the last
640kB of the file going forward, and stop at the first PCR encountered.
The problem with that was two-fold:
* It wouldn't really be the last PCR (it would be the first one within
  those last 640kB. In case of VBR files, this would put off duration
  and seek code slightly.
* It would fail on files with bitrates higher than 52Mbit/s (not common)

Instead this patch modifies that code by:
* Scanning over the last 2048kB (allows to cope with streams up to 160Mbit/s)
* Starts by the end of the file, going over chunks of 300 MPEG-TS packets
* Doesn't stop at the first PCR detected in a chunk, but instead records all
  of them, and only stop searching if there was "at least" one PCR within
  that chunk

This should improve duration reporting and seeking operations on VBR files

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