Some muxes, in particular mkv/webm, behave very differently depending on
whether we say that the stream is seekable or not (by providing the IOSeek
function). It does not help that the seek function itself returns an error.

Thus, add a new access_out control called ACCESS_OUT_CAN_SEEK, set to true
for seekable files in the file output only, and propagate the status of that
into avformat at initialization time.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>

no functional changes

Reserved stream types allocated in TREC H222.0

Sunplus chipset based cameras creates those zero sized proprietary
sections.

Signed-off-by: Tzu-Jung Lee <tjlee@ambarella.com>
Modified-and-...
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

This mostly reverts commit 8e3dd711.

If we need to axe something more...

This reverts commit 0970461e.