This patch address the issue observed with KF timestamps
and delta flag. When a section is appended before the keyframe,
it is not marked as non-delta. It's preferable to mark the
first buffer non-delta.
This patch also simplify the initial patch written by thomas,
since it does not clutter tsmux/ with a delta flag passed
around only for GStreamer convenience.
https://bugzilla.gnome.org/show_bug.cgi?id=604908
Some H264 packets can be as small as 5 bytes for repeated frames.
In such a situation the output buffer size was not big enough (5*2) to fit the
SPS/PPS header and the start codes. This corrupts the ES stream.
We now generate the SPS/PPS only once which is much more optimal and we now
know the size of the header to calculate the output buffer size more safely.
