Up until now, matroska_parse_tracks() has two main ways
to set AVCodecParameters.extradata: A generic way via CodecPrivate
(possibly with an offset) and by allocating a buffer manually;
the pointer to this buffer is stored in a stack pointer.
In particular, the latter method is problematic, as the buffer
needs to be freed manually in case of error (currently there
are no error conditions between the place where it is set
to AVCodecParameters.extradata).
Most of these buffers are very small (<= 22B), so replace
the pointer to an allocated buffer with a stack buffer
and set the extradata directly for the one place where
the buffer may not be small.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
7c95dbd94e