lavf: simplify handling of offset in av_probe_input_buuffer()

libavformat/utils.c

@@ -242,7 +242,7 @@ int av_probe_input_buffer(AVIOContext *pb, AVInputFormat **fmt,
                           const char *filename, void *logctx,
                           unsigned int offset, unsigned int max_probe_size)
 {
-    AVProbeData pd = { filename ? filename : "", NULL, -offset };
+    AVProbeData pd = { filename ? filename : "" };
     unsigned char *buf = NULL;
     int ret = 0, probe_size;
 
@@ -257,16 +257,14 @@ int av_probe_input_buffer(AVIOContext *pb, AVInputFormat **fmt,
     if (offset >= max_probe_size) {
         return AVERROR(EINVAL);
     }
+    avio_skip(pb, offset);
+    max_probe_size -= offset;
 
     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))) {
         int score = probe_size < max_probe_size ? AVPROBE_SCORE_MAX/4 : 0;
         int buf_offset = (probe_size == PROBE_BUF_MIN) ? 0 : probe_size>>1;
 
-        if (probe_size < offset) {
-            continue;
-        }
-
         /* read probe data */
         if ((ret = av_reallocp(&buf, probe_size + AVPROBE_PADDING_SIZE)) < 0)
             return ret;
@@ -280,7 +278,7 @@ int av_probe_input_buffer(AVIOContext *pb, AVInputFormat **fmt,
             ret = 0;            /* error was end of file, nothing read */
         }
         pd.buf_size += ret;
-        pd.buf = &buf[offset];
+        pd.buf       = buf;
 
         memset(pd.buf + pd.buf_size, 0, AVPROBE_PADDING_SIZE);