Implement av_get_codec_tag_string() and use it in ffprobe.

Originally committed as revision 23421 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/utils.c

@@ -802,6 +802,21 @@ static int get_bit_rate(AVCodecContext *ctx)
     return bit_rate;
 }
 
+size_t av_get_codec_tag_string(char *buf, size_t buf_size, unsigned int codec_tag)
+{
+    int i, len, ret = 0;
+
+    for (i = 0; i < 4; i++) {
+        len = snprintf(buf, buf_size,
+                       isprint(codec_tag&0xFF) ? "%c" : "[%d]", codec_tag&0xFF);
+        buf      += len;
+        buf_size  = buf_size > len ? buf_size - len : 0;
+        ret      += len;
+        codec_tag>>=8;
+    }
+    return ret;
+}
+
 void avcodec_string(char *buf, int buf_size, AVCodecContext *enc, int encode)
 {
     const char *codec_name;