lavf: Reimplement new seek API emulation

This fixes seeking to before and after files with ffplay.

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

libavformat/utils.c

@@ -1819,8 +1819,16 @@ int avformat_seek_file(AVFormatContext *s, int stream_index, int64_t min_ts, int
     //Fallback to old API if new is not implemented but old is
     //Note the old has somewat different sematics
     AV_NOWARN_DEPRECATED(
-    if(s->iformat->read_seek || 1)
+    if (s->iformat->read_seek || 1) {
-        return av_seek_frame(s, stream_index, ts, flags | (ts - min_ts > (uint64_t)(max_ts - ts) ? AVSEEK_FLAG_BACKWARD : 0));
+        int dir = (ts - min_ts > (uint64_t)(max_ts - ts) ? AVSEEK_FLAG_BACKWARD : 0);
+        int ret = av_seek_frame(s, stream_index, ts, flags | dir);
+        if (ret<0 && ts != min_ts && max_ts != ts) {
+            ret = av_seek_frame(s, stream_index, dir ? max_ts : min_ts, flags | dir);
+            if (ret >= 0)
+                ret = av_seek_frame(s, stream_index, ts, flags | (dir^AVSEEK_FLAG_BACKWARD));
+        }
+        return ret;
+    }
     )
 
     // try some generic seek like seek_frame_generic() but with new ts semantics