Change various code to use the latest Libav API. The libavcodec
error_recognition setting has been removed and replaced with different
semantics. I removed the "--lavdopts=er=<value>" option accordingly,
as I don't think it's widely enough used to be worth attempting to
emulate the old option semantics using the new API. A new option with
the new semantics can be added later if needed.
Libav dropped APIs that were necessary with all Libav versions
until quite recently (like setting avctx->age), and it would thus not
be possible to keep compatibility with previous Libav versions without
adding workarounds. The new APIs also had some bugs/limitations in the
recent Libav release 0.8, and it would not work fully (at least some
avcodec options would not be set correctly). Because of those issues,
this commit makes no attempt to maintain compatibility with anything
but the latest Libav git head. Hopefully the required fixes and
improvements will be included in a following Libav point release.
Update various code to use newer alternatives instead of deprecated
functions/fields that are being dropped at libav API bump. An
exception is avcodec_thread_init() which is being dropped even though
it's still _necessary_ with fairly recent libav versions, so there's
no good alternative which would work with both those recent versions
and latest libavcodec. I think there are grounds to consider the drop
premature and revert it for now; if that doesn't happen I'll add a
version-test #if check around it later.
