From 3d7974dbce0c010f9951e0bebc45abeb9da2a334 Mon Sep 17 00:00:00 2001
From: EthanRosenthal <ethanrosenthal@gmail.com>
Date: Sun, 4 Oct 2026 22:20:37 +0000
Subject: [PATCH] Encode the B-frame end_time test clip with explicit B-frames

test_decode_end_time_with_b_frames relied on libx264's default GOP
having B-frames. Add a b_frames option to TestVideoParameters (-bf N, plus
b-adapt=0 for libx264 so the pattern is fixed rather than adaptive) and
request 3 B-frames in that test, so it keeps exercising out-of-order
packets if encoder defaults change.
---
 src/decoder/mod.rs     | 11 +++++++----
 src/util/test_utils.rs | 12 ++++++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/decoder/mod.rs b/src/decoder/mod.rs
index 6bf5ad8..d1c4f4d 100644
--- a/src/decoder/mod.rs
+++ b/src/decoder/mod.rs
@@ -5262,9 +5262,9 @@ mod tests {
         Ok(())
     }
 
-    /// libx264 emits B-frames, so packets past the end of the window precede
-    /// in-window frames in decode order. The window must hold exactly the
-    /// frames with start <= pts < end, contiguous.
+    /// With B-frames, packets past the end of the window precede in-window
+    /// frames in decode order. The window must hold exactly the frames with
+    /// start <= pts < end, contiguous.
     #[test_case(None, 1.7, 51 ; "end only")]
     #[test_case(Some(0.5), 1.7, 36 ; "start and end")]
     fn test_decode_end_time_with_b_frames(
@@ -5273,7 +5273,10 @@ mod tests {
         expected_frames: usize,
     ) -> anyhow::Result<()> {
         init_logger();
-        let params = TestVideoParameters::default();
+        let params = TestVideoParameters {
+            b_frames: Some(3),
+            ..Default::default()
+        };
         let file = generate_test_video_file(&params)?;
         let decoded = decode_media(
             MediaDecodeRequest {
diff --git a/src/util/test_utils.rs b/src/util/test_utils.rs
index 73627de..720b7c2 100644
--- a/src/util/test_utils.rs
+++ b/src/util/test_utils.rs
@@ -23,6 +23,9 @@ pub struct TestVideoParameters {
     pub color_trc: Option<String>,
     /// FFmpeg color range tag (e.g. "tv", "pc").
     pub color_range: Option<String>,
+    /// Number of consecutive B-frames between reference frames. None keeps the
+    /// encoder default; set it when a test depends on B-frames being present.
+    pub b_frames: Option<u32>,
 }
 
 impl Default for TestVideoParameters {
@@ -41,6 +44,7 @@ impl Default for TestVideoParameters {
             color_primaries: None,
             color_trc: None,
             color_range: None,
+            b_frames: None,
         }
     }
 }
@@ -129,6 +133,9 @@ pub fn generate_test_video(
     if let Some(ref cr) = parameters.color_range {
         cmd.args(["-color_range", cr]);
     }
+    if let Some(b_frames) = parameters.b_frames {
+        cmd.args(["-bf", &b_frames.to_string()]);
+    }
 
     // libx264 does not propagate ffmpeg's -color_primaries/-color_trc flags
     // into the bitstream VUI (decoders would see them as "unknown"), so write
@@ -144,6 +151,11 @@ pub fn generate_test_video(
         if let Some(ref ct) = parameters.color_trc {
             x264_params.push(format!("transfer={ct}"));
         }
+        // -bf only caps the B-frame run; with adaptive placement libx264 can
+        // still choose fewer (or none) per GOP. Pin the pattern.
+        if parameters.b_frames.is_some() {
+            x264_params.push("b-adapt=0".to_string());
+        }
         if !x264_params.is_empty() {
             cmd.args(["-x264-params", &x264_params.join(":")]);
         }