avformat: Add a mechanism to allow demuxers to detect byte based seeking.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avformat.h

@@ -1257,6 +1257,14 @@ typedef struct AVFormatContext {
      */
 #define RAW_PACKET_BUFFER_SIZE 2500000
     int raw_packet_buffer_remaining_size;
+
+    /**
+     * IO repositioned flag.
+     * This is set by avformat when the underlaying IO context read pointer
+     * is repositioned, for example when doing byte based seeking.
+     * Demuxers can use the flag to detect such changes.
+     */
+    int io_repositioned;
 } AVFormatContext;
 
 /**

libavformat/utils.c

@@ -2018,6 +2018,8 @@ static int seek_frame_byte(AVFormatContext *s, int stream_index, int64_t pos, in
 
     avio_seek(s->pb, pos, SEEK_SET);
 
+    s->io_repositioned = 1;
+
     return 0;
 }