avcodec: Make sure codec_type is set by avcodec_get_context_defaults2

This function used to set codec_type. With the current fallback
implementation based on avcodec_get_context_defaults3, codec_type
won't be set to the value passed in, but will be set to
AVMEDIA_TYPE_UNKNOWN. Legacy callers of this function might expect
this field to be set to the value passed in.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/options.c

@@ -539,6 +539,7 @@ static const AVClass av_codec_context_class = {
 #if FF_API_ALLOC_CONTEXT
 void avcodec_get_context_defaults2(AVCodecContext *s, enum AVMediaType codec_type){
     avcodec_get_context_defaults3(s, NULL);
+    s->codec_type = codec_type;
 }
 #endif