avformat/yuv4mpegdec: fix seeking backwards

Signed-off-by: Paul B Mahol <onemda@gmail.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/libavformat/yuv4mpegdec.c b/libavformat/yuv4mpegdec.c
index ff0125e4cf..8662a42a4c 100644
--- a/libavformat/yuv4mpegdec.c
+++ b/libavformat/yuv4mpegdec.c
@@ -314,7 +314,16 @@ static int yuv4_read_packet(AVFormatContext *s, AVPacket *pkt)
 static int yuv4_read_seek(AVFormatContext *s, int stream_index,
                           int64_t pts, int flags)
 {
-    if (avio_seek(s->pb, pts * s->packet_size + s->internal->data_offset, SEEK_SET) < 0)
+    AVStream *st = s->streams[0];
+    int64_t pos;
+
+    pos = av_rescale_rnd(pts * s->packet_size,
+                         st->time_base.num,
+                         st->time_base.den * s->packet_size,
+                         (flags & AVSEEK_FLAG_BACKWARD) ? AV_ROUND_DOWN : AV_ROUND_UP);
+    pos *= s->packet_size;
+
+    if (avio_seek(s->pb, pos + s->internal->data_offset, SEEK_SET) < 0)
         return -1;
     return 0;
 }