[FFmpeg-cvslog] wtv: Speed up wtv index creation

[popcornmix]

ffmpeg | branch: master | popcornmix <popcornmix at gmail.com> | Fri Jan 29 20:27:00 2016 +0000| [def56677e58de9aaa516a738b6469747662ac372] | committer: Michael Niedermayer

wtv: Speed up wtv index creation

The index creation is O(N^2) with number of entries (typically thousands).
On a Pi this can take more than 60 seconds to execute for a recording of a few hours.

By replacing with an O(N) loop, this takes virtually zero time

Liked-by: Paul B Mahol <onemda at gmail.com>
Reviewed-by: Peter Ross <pross at xvid.org>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=def56677e58de9aaa516a738b6469747662ac372
---

 libavformat/wtvdec.c |   18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
index e8f6196..1deb4d9 100644
--- a/libavformat/wtvdec.c
+++ b/libavformat/wtvdec.c
@@ -1028,21 +1028,23 @@ static int read_header(AVFormatContext *s)
                 pb = wtvfile_open(s, root, root_size, ff_timeline_table_0_entries_Events_le16);
                 if (pb) {
                     int i;
+                    AVIndexEntry *e = wtv->index_entries;
+                    AVIndexEntry *e_end = wtv->index_entries + wtv->nb_index_entries - 1;
+                    uint64_t last_position = 0;
                     while (1) {
                         uint64_t frame_nb = avio_rl64(pb);
                         uint64_t position = avio_rl64(pb);
+                        while (frame_nb > e->size && e <= e_end) {
+                            e->pos = last_position;
+                            e++;
+                        }
                         if (avio_feof(pb))
                             break;
-                        for (i = wtv->nb_index_entries - 1; i >= 0; i--) {
-                            AVIndexEntry *e = wtv->index_entries + i;
-                            if (frame_nb > e->size)
-                                break;
-                            if (position > e->pos)
-                                e->pos = position;
-                        }
+                        last_position = position;
                     }
+                    e_end->pos = last_position;
                     wtvfile_close(pb);
-                    st->duration = wtv->index_entries[wtv->nb_index_entries - 1].timestamp;
+                    st->duration = e_end->timestamp;
                 }
             }
         }