Original commit message from CVS:
* gst/qtdemux/qtdemux.c: (gst_qtdemux_prepare_current_sample),
(gst_qtdemux_chain), (gst_qtdemux_add_stream), (qtdemux_dump_stsz),
(qtdemux_dump_stco), (qtdemux_parse_trak):
Don't make rounding errors in timestamp/duration calculations.
Fix timestamps for AMR and IMA4.  Fixes (#337436).
Create a dummy segment even when there is no edit list.