diff --git a/libavformat/internal.h b/libavformat/internal.h
index 685b550673..1f19001343 100644
--- a/libavformat/internal.h
+++ b/libavformat/internal.h
@@ -37,4 +37,24 @@ void ff_interleave_add_packet(AVFormatContext *s, AVPacket *pkt,
 
 void av_read_frame_flush(AVFormatContext *s);
 
+/**
+ * Probes a bytestream to determine the input format. Each time a
+ * probe returns with a score that is too low, the probe buffer size
+ * is increased and another attempt is made. When the maximum probe
+ * size is reached, the input format with the highest score is
+ * returned.
+ *
+ * @param pb the bytestream to probe, it may be closed and opened again
+ * @param fmt the input format is put here
+ * @param filename the filename of the stream
+ * @param logctx the log context
+ * @param offset the offset within the bytestream to probe from
+ * @param max_probe_size the maximum probe buffer size (zero for default)
+ * @return 0 if OK, a negative value corresponding to an AVERROR(xxx)
+ * code otherwise
+ */
+int ff_probe_input_buffer(ByteIOContext **pb, AVInputFormat **fmt,
+                          const char *filename, void *logctx,
+                          unsigned int offset, unsigned int max_probe_size);
+
 #endif /* AVFORMAT_INTERNAL_H */
diff --git a/libavformat/utils.c b/libavformat/utils.c
index 080f4bdded..f9d497c97f 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -465,12 +465,71 @@ int av_open_input_stream(AVFormatContext **ic_ptr,
 #define PROBE_BUF_MIN 2048
 #define PROBE_BUF_MAX (1<<20)
 
+int ff_probe_input_buffer(ByteIOContext **pb, AVInputFormat **fmt,
+                          const char *filename, void *logctx,
+                          unsigned int offset, unsigned int max_probe_size)
+{
+    AVProbeData pd = { filename ? filename : "", NULL, -offset };
+    unsigned char *buf = NULL;
+    int probe_size;
+
+    if (!max_probe_size) {
+        max_probe_size = PROBE_BUF_MAX;
+    } else if (max_probe_size > PROBE_BUF_MAX) {
+        max_probe_size = PROBE_BUF_MAX;
+    } else if (max_probe_size < PROBE_BUF_MIN) {
+        return AVERROR(EINVAL);
+    }
+
+    if (offset >= max_probe_size) {
+        return AVERROR(EINVAL);
+    }
+
+    for(probe_size= PROBE_BUF_MIN; probe_size<=max_probe_size && !*fmt; probe_size<<=1){
+        int ret, 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 */
+        buf = av_realloc(buf, probe_size + AVPROBE_PADDING_SIZE);
+        if ((ret = get_buffer(*pb, buf + buf_offset, probe_size - buf_offset)) < 0) {
+            av_free(buf);
+            return ret;
+        }
+        pd.buf_size += ret;
+        pd.buf = &buf[offset];
+
+        memset(pd.buf + pd.buf_size, 0, AVPROBE_PADDING_SIZE);
+
+        /* guess file format */
+        *fmt = av_probe_input_format2(&pd, 1, &score);
+        if(*fmt){
+            if(score <= AVPROBE_SCORE_MAX/4){ //this can only be true in the last iteration
+                av_log(logctx, AV_LOG_WARNING, "Format detected only with low score of %d, misdetection possible!\n", score);
+            }else
+                av_log(logctx, AV_LOG_DEBUG, "Probed with size=%d and score=%d\n", probe_size, score);
+        }
+    }
+
+    av_free(buf);
+    if (url_fseek(*pb, 0, SEEK_SET) < 0) {
+        url_fclose(*pb);
+        if (url_fopen(pb, filename, URL_RDONLY) < 0)
+            return AVERROR(EIO);
+    }
+
+    return 0;
+}
+
 int av_open_input_file(AVFormatContext **ic_ptr, const char *filename,
                        AVInputFormat *fmt,
                        int buf_size,
                        AVFormatParameters *ap)
 {
-    int err, probe_size;
+    int err;
     AVProbeData probe_data, *pd = &probe_data;
     ByteIOContext *pb = NULL;
     void *logctx= ap && ap->prealloced_context ? *ic_ptr : NULL;
@@ -496,37 +555,9 @@ int av_open_input_file(AVFormatContext **ic_ptr, const char *filename,
         if (buf_size > 0) {
             url_setbufsize(pb, buf_size);
         }
-
-        for(probe_size= PROBE_BUF_MIN; probe_size<=PROBE_BUF_MAX && !fmt; probe_size<<=1){
-            int score= probe_size < PROBE_BUF_MAX ? AVPROBE_SCORE_MAX/4 : 0;
-            /* read probe data */
-            pd->buf= av_realloc(pd->buf, probe_size + AVPROBE_PADDING_SIZE);
-            pd->buf_size = get_buffer(pb, pd->buf, probe_size);
-
-            if ((int)pd->buf_size < 0) {
-                err = pd->buf_size;
-                goto fail;
-            }
-
-            memset(pd->buf+pd->buf_size, 0, AVPROBE_PADDING_SIZE);
-            if (url_fseek(pb, 0, SEEK_SET) < 0) {
-                url_fclose(pb);
-                if (url_fopen(&pb, filename, URL_RDONLY) < 0) {
-                    pb = NULL;
-                    err = AVERROR(EIO);
-                    goto fail;
-                }
-            }
-            /* guess file format */
-            fmt = av_probe_input_format2(pd, 1, &score);
-            if(fmt){
-                if(score <= AVPROBE_SCORE_MAX/4){ //this can only be true in the last iteration
-                    av_log(logctx, AV_LOG_WARNING, "Format detected only with low score of %d, misdetection possible!\n", score);
-                }else
-                    av_log(logctx, AV_LOG_DEBUG, "Probed with size=%d and score=%d\n", probe_size, score);
-            }
+        if ((err = ff_probe_input_buffer(&pb, &fmt, filename, logctx, 0, 0)) < 0) {
+            goto fail;
         }
-        av_freep(&pd->buf);
     }
 
     /* if still no format found, error */