add seeking support in ASS demuxer

Originally committed as revision 24578 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/assdec.c

@@ -162,6 +162,46 @@ static int read_packet(AVFormatContext *s, AVPacket *pkt)
     return 0;
 }
 
+static int read_seek2(AVFormatContext *s, int stream_index,
+                      int64_t min_ts, int64_t ts, int64_t max_ts, int flags)
+{
+    ASSContext *ass = s->priv_data;
+
+    if (flags & AVSEEK_FLAG_BYTE) {
+        return AVERROR_NOTSUPP;
+    } else if (flags & AVSEEK_FLAG_FRAME) {
+        if (ts < 0 || ts >= ass->event_count)
+            return AVERROR(ERANGE);
+        ass->event_index = ts;
+    } else {
+        int i, idx = -1;
+        int64_t min_ts_diff = INT64_MAX;
+        if (stream_index == -1) {
+            AVRational time_base = s->streams[0]->time_base;
+            ts = av_rescale_q(ts, AV_TIME_BASE_Q, time_base);
+            min_ts = av_rescale_rnd(min_ts, time_base.den,
+                                    time_base.num * (int64_t)AV_TIME_BASE,
+                                    AV_ROUND_UP);
+            max_ts = av_rescale_rnd(max_ts, time_base.den,
+                                    time_base.num * (int64_t)AV_TIME_BASE,
+                                    AV_ROUND_DOWN);
+        }
+        /* TODO: ass->event[] is sorted by pts so we could do a binary search */
+        for (i=0; i<ass->event_count; i++) {
+            int64_t pts = get_pts(ass->event[i]);
+            int64_t ts_diff = FFABS(pts - ts);
+            if (pts >= min_ts && pts <= max_ts && ts_diff < min_ts_diff) {
+                min_ts_diff = ts_diff;
+                idx = i;
+            }
+        }
+        if (idx < 0)
+            return AVERROR(ERANGE);
+        ass->event_index = idx;
+    }
+    return 0;
+}
+
 AVInputFormat ass_demuxer = {
     "ass",
     NULL_IF_CONFIG_SMALL("Advanced SubStation Alpha subtitle format"),
@@ -170,5 +210,5 @@ AVInputFormat ass_demuxer = {
     read_header,
     read_packet,
     read_close,
-//    read_seek,
+    .read_seek2  = read_seek2,
 };