avformat: Add ff_configure_buffers_for_index()

This allows configuring the io buffer in such way that few seeks are needed for playback
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/internal.h

@@ -254,6 +254,8 @@ int ff_add_index_entry(AVIndexEntry **index_entries,
                        unsigned int *index_entries_allocated_size,
                        int64_t pos, int64_t timestamp, int size, int distance, int flags);
 
+void ff_configure_buffers_for_index(AVFormatContext *s, int64_t time_tolerance);
+
 /**
  * Add a new chapter.
  *

libavformat/utils.c

@@ -1781,6 +1781,45 @@ int ff_index_search_timestamp(const AVIndexEntry *entries, int nb_entries,
     return m;
 }
 
+void ff_configure_buffers_for_index(AVFormatContext *s, int64_t time_tolerance)
+{
+    int ist1, ist2;
+    int64_t pos_delta = 0;
+
+    for (ist1 = 0; ist1 < s->nb_streams; ist1++) {
+        AVStream *st1 = s->streams[ist1];
+        for (ist2 = 0; ist2 < s->nb_streams; ist2++) {
+            AVStream *st2 = s->streams[ist2];
+            int i1, i2;
+
+            if (ist1 == ist2)
+                continue;
+
+            for (i1 = i2 = 0; i1 < st1->nb_index_entries; i1++) {
+                AVIndexEntry *e1 = &st1->index_entries[i1];
+                int64_t e1_pts = av_rescale_q(e1->timestamp, st1->time_base, AV_TIME_BASE_Q);
+
+                for (; i2 < st2->nb_index_entries; i2++) {
+                    AVIndexEntry *e2 = &st2->index_entries[i2];
+                    int64_t e2_pts = av_rescale_q(e2->timestamp, st2->time_base, AV_TIME_BASE_Q);
+                    if (e2_pts - e1_pts < time_tolerance)
+                        continue;
+                    pos_delta = FFMAX(pos_delta, e1->pos - e2->pos);
+                    break;
+                }
+            }
+        }
+    }
+
+    pos_delta *= 2;
+    /* XXX This could be adjusted depending on protocol*/
+    if (s->pb->buffer_size < pos_delta && pos_delta < (1<<24)) {
+        av_log(s, AV_LOG_VERBOSE, "Reconfiguring buffers to size %"PRId64"\n", pos_delta);
+        ffio_set_buf_size(s->pb, pos_delta);
+        s->pb->short_seek_threshold = FFMAX(s->pb->short_seek_threshold, pos_delta/2);
+    }
+}
+
 int av_index_search_timestamp(AVStream *st, int64_t wanted_timestamp, int flags)
 {
     return ff_index_search_timestamp(st->index_entries, st->nb_index_entries,