avformat: Change avpriv_new_chapter() from O(n) to (1) in the common case

Fixes: timeout (slow -> 300ms)
Fixes: 28876/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-5664824587583488

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

1 files changed, 8 insertions, 3 deletions

diff --git a/libavformat/utils.c b/libavformat/utils.c
index 1ec71691e5..9dab4fc96f 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -4614,9 +4614,14 @@ AVChapter *avpriv_new_chapter(AVFormatContext *s, int id, AVRational time_base,
         return NULL;
     }
 
-    for (i = 0; i < s->nb_chapters; i++)
-        if (s->chapters[i]->id == id)
-            chapter = s->chapters[i];
+    if (!s->nb_chapters) {
+        s->internal->chapter_ids_monotonic = 1;
+    } else if (!s->internal->chapter_ids_monotonic || s->chapters[s->nb_chapters-1]->id >= id) {
+        s->internal->chapter_ids_monotonic = 0;
+        for (i = 0; i < s->nb_chapters; i++)
+            if (s->chapters[i]->id == id)
+                chapter = s->chapters[i];
+    }
 
     if (!chapter) {
         chapter = av_mallocz(sizeof(AVChapter));