Original commit message from CVS:
* gst/matroska/matroska-demux.c:
(gst_matroska_demux_parse_blockgroup_or_simpleblock):
If a gap of more than 1/2 second is found in one stream send a
NEWSEGMENT event to not stall the pipeline if the gap is too large.
This also fixes Matroska files where the first buffer doesn't start
at timestamp 0. Fixes bug #429322.
The duration of a block is the default duration multiplied with the
number of laces. Every lace is one frame and the default duration
is the duration of one frame. This fixes playback of files that use
lacing for some tracks.