[Bug 791495] New: h265parse: Messes up timestamps for byte-stream

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=791495

            Bug ID: 791495
           Summary: h265parse: Messes up timestamps for byte-stream
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: All
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: matej.knopp at gmail.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

It happens when previous frame has trailing zero. Parser split frame too early,
leaving trailing zeros as prefix for new frame, which results in messed up
timestamps.

Caused by following code in gst_h265_parser_identify_nalu

  /* Mini performance improvement:
   * We could have a way to store how many 0s were skipped to avoid
   * parsing them again on the next NAL */
  while (off2 > 0 && data[nalu->offset + off2 - 1] == 00)
    off2--;

Annex B does says that there should be zero byte before AU startcode, however
it also says that during parsing the zero byte should be discarded. So maybe
determining the timestamp from zero byte is not a very good idea.

The stream already parsed by FFMPEG HEVC parser, which seems to leave zero byte
trailing, but that doesn't mean such files can't be encountered in the wild.

Btw. Why's there loop? Why skipping more than 1 zero byte? Doesn't that just
increases chance of messed up timestamps?

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