https://bugzilla.gnome.org/show_bug.cgi?id=639121

This was causing keyframe_granule to be set to 0 for all streams
when seeking to the beginning of the stream, i.e., at the
beginning of playback.  Fixes #619778.

Don't try to stream data on pads that are not added yet. This happens while we
discover the different streams.

This will allow switching from one stream to another without having to send
the headers for the new stream again.

https://bugzilla.gnome.org/show_bug.cgi?id=637927

allocate buffers using gst_buffer_new_and_alloc() instead of
gst_pad_alloc_buffer_and_set_caps(), as the first one will
cause the pad to block, and we don't want that since that will
prevent subsequent pads from being fed if a block occurs at
start, when all pads must be fed for playback to start.

This fixes autoplugging of the tiger element and other things.

https://bugzilla.gnome.org/show_bug.cgi?id=637822

https://bugzilla.gnome.org/show_bug.cgi?id=637519

In particular, move comment header parsing to gstoggstrem.c.
Thanks to Felipe Contreras.

Fixes #629349 (partially).

Oggdemux will currently try to pad alloc a buffer from the peer when it is
reading the header files. This is a relic from the time where we had an internal
parser and needs to be removed at some point in time.

The problem is that when there is no peer pad yet (which is normal when
collecting headers) we should still continue to parse all the packets of a
page instead of erroring out on NOT_LINKED.

Fixes #632167

Only keep the last valid granulepos we see when scanning the last
pages. It is possible that the last page that we inspect has a -1 granulepos, in
which case we want to keep the previous valid time instead.

Fixes #631703

Files with a skeleton, or other files with a stream that ends before the end of
the chain would start playing from the end of the chain when trying to seek with
a negative rate at a position between the end of any stream and the end of the
chain.

This is due to the loop in _do_seek() assuming that pages will be encountered
for all streams shortly after the place where we want to seek, as found by
do_binary_search().

In the first iteration of the loop, stream ends are now checked against the
time of the current page.

The pad might be linked later and after resetting it it will
only work after resetting all of oggdemux.

And while we're at it, handle WRONG_STATE as error too
in oggdemux and WRONG_STATE and NOT_LINKED in oggaviparse.

If the source element failed here, oggdemux would crash.

Fixes #623218.

It will crash later and shouldn't really happen anyway unless
something is really wrong.

Fixes bug #620939, see bug #607945.

Avoid a crash when we try to seek when there is no current chain.

Ignore the skeleton start time as it is usually wrong for live streams
and we have the needed logic to calculate it anyway.

Wait until we have all the stream headers before we start exposing the streams
of a chain.

When we have an index, use it to much more accurately estimate the total stream
bitrate.

When seeking in push mode, try to use the index first before we use the bitrate
estimation.