[FFmpeg-devel] [PATCH 1/2] libavformat: Improve ff_configure_buffers_for_index for excessive deltas

[Martin Storsjö]

Previously, the ff_configure_buffers_for_index function had
upper sanity limits of 16 MB (1<<24) for buffer_size and
8 MB (1<<23) for short_seek_threshold.

However, if the index analysis showed a need for even larger
buffer sizes (for a really badly interleaved file), over the
sanity limits, we previously didn't increase the buffer sizes
at all.

Instead, if the file shows a need for really large buffers and
short_seek_threshold, just set them to the maximum sanity limit;
while it might not be enough for all cases in the file, it might
be enough for most of it.

This can happen e.g. with a mov file with some tracks containing
some samples that belong in the start of the file, at the end of
the mdat, while the rest of the file is mostly reasonably interleaved;
previously those samples caused the maximum pos_delta to skyrocket,
skipping any buffer size enlargement.

Signed-off-by: Martin Storsjö <martin at martin.st>
---
 libavformat/seek.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libavformat/seek.c b/libavformat/seek.c
index a236e285c0..818549dfef 100644
--- a/libavformat/seek.c
+++ b/libavformat/seek.c
@@ -220,7 +220,8 @@ void ff_configure_buffers_for_index(AVFormatContext *s, int64_t time_tolerance)
     pos_delta *= 2;
     ctx = ffiocontext(s->pb);
     /* XXX This could be adjusted depending on protocol*/
-    if (s->pb->buffer_size < pos_delta && pos_delta < (1<<24)) {
+    pos_delta = FFMIN(pos_delta, 1<<24);
+    if (s->pb->buffer_size < pos_delta) {
         av_log(s, AV_LOG_VERBOSE, "Reconfiguring buffers to size %"PRId64"\n", pos_delta);
 
         /* realloc the buffer and the original data will be retained */
@@ -232,9 +233,8 @@ void ff_configure_buffers_for_index(AVFormatContext *s, int64_t time_tolerance)
         ctx->short_seek_threshold = FFMAX(ctx->short_seek_threshold, pos_delta/2);
     }
 
-    if (skip < (1<<23)) {
-        ctx->short_seek_threshold = FFMAX(ctx->short_seek_threshold, skip);
-    }
+    skip = FFMIN(skip, 1<<23);
+    ctx->short_seek_threshold = FFMAX(ctx->short_seek_threshold, skip);
 }
 
 int av_index_search_timestamp(AVStream *st, int64_t wanted_timestamp, int flags)
-- 
2.37.1 (Apple Git-137.1)