[FFmpeg-devel] [PATCH 3/4] avformat/mov: Only read the mfra size once during sidx parsing

[Derek Buitenhuis]

On files with more than one sidx box, like live fragmented MP4
files, it was previously re-reading and seeking on every singl
sidx box, leading to extremely poor performance on larger files,
especially over the network.

Only do it on the first one, and stash its result.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis at gmail.com>
---
 libavformat/isom.h |  2 ++
 libavformat/mov.c  | 16 +++++++++-------
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/libavformat/isom.h b/libavformat/isom.h
index 41a9c64c11..78495fd336 100644
--- a/libavformat/isom.h
+++ b/libavformat/isom.h
@@ -291,6 +291,8 @@ typedef struct MOVContext {
     int decryption_key_len;
     int enable_drefs;
     int32_t movie_display_matrix[3][3]; ///< display matrix from mvhd
+    int have_read_mfra_size;
+    uint32_t mfra_size;
 } MOVContext;
 
 int ff_mp4_read_descr_len(AVIOContext *pb);
diff --git a/libavformat/mov.c b/libavformat/mov.c
index 49c2d05d21..e33031f158 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -5097,14 +5097,16 @@ static int mov_read_sidx(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     if (!is_complete && (pb->seekable & AVIO_SEEKABLE_NORMAL)) {
         int64_t ret;
         int64_t original_pos = avio_tell(pb);
-        int32_t mfra_size;
-        if ((ret = avio_seek(pb, stream_size - 4, SEEK_SET)) < 0)
-            return ret;
-        mfra_size = avio_rb32(pb);
-        if (offset + mfra_size == stream_size)
+        if (!c->have_read_mfra_size) {
+            if ((ret = avio_seek(pb, stream_size - 4, SEEK_SET)) < 0)
+                return ret;
+            c->mfra_size = avio_rb32(pb);
+            c->have_read_mfra_size = 1;
+            if ((ret = avio_seek(pb, original_pos, SEEK_SET)) < 0)
+                return ret;
+        }
+        if (offset + c->mfra_size == stream_size)
             is_complete = 1;
-        if ((ret = avio_seek(pb, original_pos, SEEK_SET)) < 0)
-            return ret;
     }
 
     if (is_complete) {
-- 
2.28.0