seeking stuff

  adaptively change middle position selection algo for seeking, this avoids some ugly worstcases of the interpolated variant
  avoid backward search for mpeg where possible, its 17 times slower then forward according to my benchmark

Originally committed as revision 2710 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 45 insertions, 42 deletions

diff --git a/libavformat/mpeg.c b/libavformat/mpeg.c
index 8fa4cf3fe1..447b6d483d 100644
--- a/libavformat/mpeg.c
+++ b/libavformat/mpeg.c
@@ -1037,9 +1037,9 @@ static int64_t mpegps_read_dts(AVFormatContext *s, int stream_index,
 static int mpegps_read_seek(AVFormatContext *s, 
                             int stream_index, int64_t timestamp)
 {
-    int64_t pos_min, pos_max, pos;
+    int64_t pos_min, pos_max, pos, pos_limit;
     int64_t dts_min, dts_max, dts;
-    int index;
+    int index, no_change;
     AVStream *st;
 
     timestamp = (timestamp * 90000) / AV_TIME_BASE;
@@ -1057,6 +1057,7 @@ static int mpegps_read_seek(AVFormatContext *s,
     
     dts_max=
     dts_min= AV_NOPTS_VALUE;
+    pos_limit= -1; //gcc falsely says it may be uninitalized
 
     st= s->streams[stream_index];
     if(st->index_entries){
@@ -1080,6 +1081,7 @@ static int mpegps_read_seek(AVFormatContext *s,
             assert(e->timestamp >= timestamp);
             pos_max= e->pos;
             dts_max= e->timestamp;
+            pos_limit= pos_max - e->min_distance;
 #ifdef DEBUG_SEEK
         printf("unsing cached pos_max=0x%llx dts_max=%0.3f\n", 
                pos_max,dts_max / 90000.0);
@@ -1099,61 +1101,62 @@ static int mpegps_read_seek(AVFormatContext *s,
     if(dts_max == AV_NOPTS_VALUE){
         pos_max = url_filesize(url_fileno(&s->pb)) - 1;
         dts_max = mpegps_read_dts(s, stream_index, &pos_max, 0);
+        pos_limit= pos_max;
     }
-    
-    while (pos_min <= pos_max) {
+
+    no_change=0;
+    while (pos_min < pos_limit) {
 #ifdef DEBUG_SEEK
         printf("pos_min=0x%llx pos_max=0x%llx dts_min=%0.3f dts_max=%0.3f\n", 
                pos_min, pos_max,
                dts_min / 90000.0, dts_max / 90000.0);
 #endif
-        if (timestamp <= dts_min) {
-            pos = pos_min;
-            goto found;
-        } else if (timestamp >= dts_max) {
-            pos = pos_max;
-            goto found;
-        } else {
-            /* interpolate position (better than dichotomy) */
-            pos = (int64_t)((double)(pos_max - pos_min) * 
+        int64_t start_pos;
+        assert(pos_limit <= pos_max);
+
+        if(no_change==0){
+            int64_t approximate_keyframe_distance= pos_max - pos_limit;
+            // interpolate position (better than dichotomy)
+            pos = (int64_t)((double)(pos_max - pos_min) *
                             (double)(timestamp - dts_min) /
-                            (double)(dts_max - dts_min)) + pos_min;
+                            (double)(dts_max - dts_min)) + pos_min - approximate_keyframe_distance;
+        }else if(no_change==1){
+            // bisection, if interpolation failed to change min or max pos last time
+            pos = (pos_min + pos_limit)>>1;
+        }else{
+            // linear search if bisection failed, can only happen if there are very few or no keframes between min/max
+            pos=pos_min;
         }
+        if(pos <= pos_min)
+            pos= pos_min + 1;
+        else if(pos > pos_limit)
+            pos= pos_limit;
+        start_pos= pos;
+
+        // read the next timestamp 
+    	dts = mpegps_read_dts(s, stream_index, &pos, 1);
+        if(pos == pos_max)
+            no_change++;
+        else
+            no_change=0;
 #ifdef DEBUG_SEEK
-        printf("pos=0x%llx\n", pos);
+printf("%Ld %Ld %Ld / %Ld %Ld %Ld target:%Ld limit:%Ld start:%Ld noc:%d\n", pos_min, pos, pos_max, dts_min, dts, dts_max, timestamp, pos_limit, start_pos, no_change);
 #endif
-        /* read the next timestamp */
-        dts = mpegps_read_dts(s, stream_index, &pos, 1);
-        /* check if we are lucky */
-        if (dts == AV_NOPTS_VALUE) {
-            /* should never happen */
-            pos = pos_min;
-            goto found;
-        } else if (timestamp == dts) {
-            goto found;
-        } else if (timestamp < dts) {
+        assert(dts != AV_NOPTS_VALUE);
+        if (timestamp < dts) {
+            pos_limit = start_pos - 1;
             pos_max = pos;
-            dts_max = mpegps_read_dts(s, stream_index, &pos_max, 0);
-            if (dts_max == AV_NOPTS_VALUE) {
-                /* should never happen */
-                break;
-            } else if (timestamp >= dts_max) {
-                pos = pos_max;
-                goto found;
-            }
+            dts_max = dts;
         } else {
-            pos_min = pos + 1;
-            dts_min = mpegps_read_dts(s, stream_index, &pos_min, 1);
-            if (dts_min == AV_NOPTS_VALUE) {
-                /* should never happen */
-                goto found;
-            } else if (timestamp <= dts_min) {
-                goto found;
-            }
+            pos_min = pos;
+            dts_min = dts;
+            /* check if we are lucky */
+            if (timestamp == dts)
+                break;
         }
     }
+    
     pos = pos_min;
- found:
 #ifdef DEBUG_SEEK
     pos_min = pos;
     dts_min = mpegps_read_dts(s, stream_index, &pos_min, 1);