img2dec: seeking support

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

libavformat/img2dec.c

@@ -393,6 +393,7 @@ static int img_read_packet(AVFormatContext *s1, AVPacket *pkt)
         return AVERROR(ENOMEM);
     pkt->stream_index = 0;
     pkt->flags       |= AV_PKT_FLAG_KEY;
+    pkt->pts          = s->img_number - s->img_first;
 
     pkt->size = 0;
     for (i = 0; i < 3; i++) {
@@ -426,6 +427,16 @@ static int img_read_close(struct AVFormatContext* s1)
     return 0;
 }
 
+static int img_read_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags)
+{
+    VideoDemuxData *s1 = s->priv_data;
+
+    if (timestamp < 0 || timestamp > s1->img_last - s1->img_first)
+        return -1;
+    s1->img_number = timestamp + s1->img_first;
+    return 0;
+}
+
 #define OFFSET(x) offsetof(VideoDemuxData, x)
 #define DEC AV_OPT_FLAG_DECODING_PARAM
 static const AVOption options[] = {
@@ -460,6 +471,7 @@ AVInputFormat ff_image2_demuxer = {
     .read_header    = img_read_header,
     .read_packet    = img_read_packet,
     .read_close     = img_read_close,
+    .read_seek      = img_read_seek,
     .flags          = AVFMT_NOFILE,
     .priv_class     = &img2_class,
 };