Set the fields of the given AVCodecContext to default values corresponding
to the given codec (defaults may be codec-dependent).
Do not call this function if a non-NULL codec has been passed
to avcodec_alloc_context3() that allocated this AVCodecContext.
If codec is non-NULL, it is illegal to call avcodec_open2() with a
different codec on this AVCodecContext.
Set the fields of the given AVCodecContext to default values corresponding to the given codec (defaults may be codec-dependent).
Do not call this function if a non-NULL codec has been passed to avcodec_alloc_context3() that allocated this AVCodecContext. If codec is non-NULL, it is illegal to call avcodec_open2() with a different codec on this AVCodecContext.