New codec probing system try #1.

Originally committed as revision 14184 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -313,6 +313,8 @@ enum CodecID {
     /* other specific kind of codecs (generally used for attachments) */
     CODEC_ID_TTF= 0x18000,
 
+    CODEC_ID_PROBE= 0x19000, ///< codec_id is not known (like CODEC_ID_NONE) but lavf should attempt to identify it
+
     CODEC_ID_MPEG2TS= 0x20000, /**< _FAKE_ codec to indicate a raw MPEG-2 TS
                                 * stream (only used by libavformat) */
 };