From 6edb188899b0aa2c664cb09ab185678d69d3592a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Fri, 27 May 2022 11:05:36 +0300
Subject: [PATCH] fmp4mux: Fix usage of first_sample_flags/default_sample_flags

Previously first_sample_flags was never used so if the first sample was
a keyframe and all others not then each sample got its own flags.
---
 generic/fmp4/src/fmp4mux/boxes.rs | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/generic/fmp4/src/fmp4mux/boxes.rs b/generic/fmp4/src/fmp4mux/boxes.rs
index 47612141b..befdf4953 100644
--- a/generic/fmp4/src/fmp4mux/boxes.rs
+++ b/generic/fmp4/src/fmp4mux/boxes.rs
@@ -1624,12 +1624,11 @@ fn analyze_buffers(
         let f = sample_flags_from_buffer(buffer, intra_only);
         if first_buffer_flags.is_none() {
             first_buffer_flags = Some(f);
+        } else {
             flags = Some(f);
-        } else if flags.is_none() {
             if Some(f) != first_buffer_flags {
                 tr_flags |= FIRST_SAMPLE_FLAGS_PRESENT;
             }
-            flags = Some(f);
         }
 
         if flags.is_some() && Some(f) != flags {
@@ -1686,6 +1685,13 @@ fn analyze_buffers(
         duration = None;
     }
 
+    // If there is only a single buffer use its flags as default sample flags
+    // instead of first sample flags.
+    if flags.is_none() && first_buffer_flags.is_some() {
+        tr_flags &= !FIRST_SAMPLE_FLAGS_PRESENT;
+        flags = first_buffer_flags.take();
+    }
+
     if (tr_flags & SAMPLE_FLAGS_PRESENT) == 0 {
         tf_flags |= DEFAULT_SAMPLE_FLAGS_PRESENT;
     } else {