avformat: use const char* instead of uint8_t* for AVProbeData.mime_type

This makes the field consistent with AVInputFormat.mime_type and the
argument type of av_match_name.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavformat/avformat.h

@@ -396,7 +396,7 @@ typedef struct AVProbeData {
     const char *filename;
     unsigned char *buf; /**< Buffer must have AVPROBE_PADDING_SIZE of extra allocated bytes filled with zero. */
     int buf_size;       /**< Size of buf except extra allocated bytes */
-    uint8_t *mime_type; /**< mime_type, when known. */
+    const char *mime_type; /**< mime_type, when known. */
 } AVProbeData;
 
 #define AVPROBE_SCORE_EXTENSION  50 ///< score for file extension

libavformat/format.c

@@ -242,6 +242,7 @@ int av_probe_input_buffer(AVIOContext *pb, AVInputFormat **fmt,
     AVProbeData pd = { filename ? filename : "" };
     uint8_t *buf = NULL;
     int ret = 0, probe_size;
+    uint8_t *mime_type_opt = NULL;
 
     if (!max_probe_size)
         max_probe_size = PROBE_BUF_MAX;
@@ -254,8 +255,11 @@ int av_probe_input_buffer(AVIOContext *pb, AVInputFormat **fmt,
         return AVERROR(EINVAL);
     avio_skip(pb, offset);
     max_probe_size -= offset;
-    if (pb->av_class)
-        av_opt_get(pb, "mime_type", AV_OPT_SEARCH_CHILDREN, &pd.mime_type);
+    if (pb->av_class) {
+        av_opt_get(pb, "mime_type", AV_OPT_SEARCH_CHILDREN, &mime_type_opt);
+        pd.mime_type = (const char *)mime_type_opt;
+        mime_type_opt = NULL;
+    }
     for (probe_size = PROBE_BUF_MIN; probe_size <= max_probe_size && !*fmt;
          probe_size = FFMIN(probe_size << 1,
                             FFMAX(max_probe_size, probe_size + 1))) {
@@ -301,6 +305,6 @@ fail:
         (ret = ffio_rewind_with_probe_data(pb, buf, pd.buf_size)) < 0) {
         av_free(buf);
     }
-    av_free(pd.mime_type);
+    av_freep(&pd.mime_type);
     return ret;
 }