When the mux is capable of marking blocks as containing keyframes
(currently only the avformat mux), start new clients only on such
frames. This makes sure they do not get anything they might not
decode at the beginning of the stream.

This patch completes WebM streaming support.
Signed-off-by: Rafaël Carré <funman@videolan.org>

Sample:
http://www.photoflashgraphics.com/designers_portfolio/premiere_movies/multimedia_movies/bellair_digital_movie.asfSigned-off-by: Jean-Baptiste Kempf <jb@videolan.org>

This was often confusing external plugin authors.

This works around an automake limitation with multiple directory
prefixes.

Upstream is gone. Maintainer has left. Build system support is missing.

It is a bit odd that both inline and external flags are mixed together.
This might be an old silent bug.

This relies contrib version of x262 that gives x262.h and all. Otherwise
it seems to be pretty hard to have x264/x26410b/x262 in the same time.

Use Write-function and refactored functions to check that in flushing
we don't write too long last segment but split it in multiple segments
if needed. Fixes #9383