AVCodecContext release_buffer() shall be NULL for audio codecs using
get_buffer. The backward compatibility code hence have to check before
calling it.

Fixes memleaks when frame mt is used and the decoder is not flushed at
the end.

CC:libav-stable@libav.org

CC:libav-stable@libav.org

The svq3 decoder does not call ff_h264_frame_start() anymore.

The h264 decoder does not use mpegvideo anymore. The svq3 decoder only
uses ff_draw_horiz_band().

The mingw win32 atomics appear to be faulty, so they should not be used
if the gcc ones are available.
Signed-off-by: Martin Storsjö <martin@martin.st>

Fixes video playback in applications still using reordered_opaque.

Return an error on incomplete frames.

Fixes a memleak due to avcodec_free_frame not freeing the frame data.

planes - FF_ARRAY_ELEMS would be evaluated as unsigned and underflow
instead of being negative as was intended.

Avoid buffer overflow in buffer_needs_copy()
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

SDL 2 is API incompatible.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>