lavc: add support for filtering packets before decoding

libavcodec/avcodec.h

@@ -3243,6 +3243,12 @@ typedef struct AVCodec {
      * See FF_CODEC_CAP_* in internal.h
      */
     int caps_internal;
+
+    /**
+     * Decoding only, a comma-separated list of bitstream filters to apply to
+     * packets before decoding.
+     */
+    const char *bsfs;
 } AVCodec;
 
 /**