From df3dac8982a17fb7e1754d449d7c4f9154b7c08e Mon Sep 17 00:00:00 2001
From: Brandon Thomas <echelon@gmail.com>
Date: Wed, 8 Apr 2026 10:00:10 -0400
Subject: [PATCH] ffmpeg transcode

---
 .../src/ffmpeg/ffmpeg_transcode_to_mp4.rs     | 134 ++++++++++++++++++
 crates/lib/ffmpeg_utils/src/ffmpeg/mod.rs     |   1 +
 2 files changed, 135 insertions(+)
 create mode 100644 crates/lib/ffmpeg_utils/src/ffmpeg/ffmpeg_transcode_to_mp4.rs

diff --git a/crates/lib/ffmpeg_utils/src/ffmpeg/ffmpeg_transcode_to_mp4.rs b/crates/lib/ffmpeg_utils/src/ffmpeg/ffmpeg_transcode_to_mp4.rs
new file mode 100644
index 0000000000..8cb51c7a32
--- /dev/null
+++ b/crates/lib/ffmpeg_utils/src/ffmpeg/ffmpeg_transcode_to_mp4.rs
@@ -0,0 +1,134 @@
+use anyhow::bail;
+use log::{error, info};
+use std::io::Write;
+use std::path::Path;
+use std::process::Command;
+
+use errors::AnyhowResult;
+
+pub struct FfmpegTranscodeToMp4Args<'a> {
+  pub video_input_path: &'a Path,
+  pub video_output_path: &'a Path,
+}
+
+/// Transcode an arbitrary input video into a streaming-friendly H.264 / AAC
+/// MP4 file.
+///
+/// Output container: MP4 (faststart-enabled so the moov atom lives at the
+/// front, which makes the file usable by HTTP range-request video players
+/// before the whole thing has downloaded).
+///
+/// Output streams:
+///   - video: H.264 (libx264), yuv420p, CRF 23, "fast" preset
+///   - audio: AAC (libfdk-aac unavailable in stock ffmpeg → libmp3lame? no →
+///     plain `aac`), 128 kbps
+///
+/// Audio is transcoded rather than copied so the output is consistent
+/// regardless of the input container's audio codec.
+pub fn ffmpeg_transcode_to_mp4(args: FfmpegTranscodeToMp4Args) -> AnyhowResult<()> {
+  let mut command = Command::new("ffmpeg");
+
+  command
+      .arg("-nostdin")
+      .arg("-y")
+      .arg("-i").arg(args.video_input_path)
+      // Video: H.264, broadly compatible chroma subsampling.
+      .arg("-c:v").arg("libx264")
+      .arg("-preset").arg("fast")
+      .arg("-crf").arg("23")
+      .arg("-pix_fmt").arg("yuv420p")
+      // Audio: AAC at 128 kbps.
+      .arg("-c:a").arg("aac")
+      .arg("-b:a").arg("128k")
+      // MP4 container with the moov atom moved to the front for fast HTTP streaming.
+      .arg("-movflags").arg("+faststart")
+      .arg(args.video_output_path);
+
+  info!("Calling ffmpeg (transcode to mp4)...");
+
+  let output = command.output()?;
+
+  if !output.status.success() {
+    error!("bad exit status: {}", output.status);
+
+    let _r = std::io::stdout().write_all(&output.stdout);
+    let _r = std::io::stderr().write_all(&output.stderr);
+
+    bail!("ffmpeg transcode to mp4 failed: {:?}", output.status.to_string());
+  }
+
+  Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+  use tempdir::TempDir;
+  use test_utils::test_file_path::test_file_path;
+
+  #[test]
+  fn test_transcode_mov_to_mp4() {
+    let input_path = test_file_path("test_data/video/mov/majoras_mask_intro.mov")
+        .expect("test video should exist");
+
+    let temp_dir = TempDir::new_in("/tmp", "ffmpeg_transcode_to_mp4_test")
+        .expect("should create temp dir");
+
+    let output_path = temp_dir.path().join("transcoded.mp4");
+
+    ffmpeg_transcode_to_mp4(FfmpegTranscodeToMp4Args {
+      video_input_path: &input_path,
+      video_output_path: &output_path,
+    }).expect("ffmpeg should succeed");
+
+    // ── Output file exists and is non-empty ───────────────────────────────
+    assert!(output_path.exists(), "output mp4 should exist");
+    let metadata = std::fs::metadata(&output_path).expect("should stat output");
+    assert!(metadata.len() > 0, "output mp4 should be non-empty");
+
+    // ── ffprobe the output and assert codecs / container ──────────────────
+    let probe = ffprobe::ffprobe(&output_path)
+        .expect("ffprobe should succeed on the transcoded file");
+
+    // Container is mp4 — ffprobe reports it as either "mov,mp4,m4a,3gp,3g2,mj2"
+    // or "mp4" depending on version. Both contain "mp4".
+    let format_name = &probe.format.format_name;
+    assert!(
+      format_name.contains("mp4"),
+      "expected mp4 container, got format_name = {:?}",
+      format_name,
+    );
+
+    // Video stream is H.264.
+    let video_stream = probe.streams.iter()
+        .find(|s| s.codec_type.as_deref() == Some("video"))
+        .expect("should have a video stream");
+    assert_eq!(
+      video_stream.codec_name.as_deref(),
+      Some("h264"),
+      "expected H.264 video, got {:?}",
+      video_stream.codec_name,
+    );
+    assert_eq!(
+      video_stream.pix_fmt.as_deref(),
+      Some("yuv420p"),
+      "expected yuv420p pixel format, got {:?}",
+      video_stream.pix_fmt,
+    );
+
+    // Audio stream is AAC (if the source has audio — Majora's Mask intro does).
+    let audio_stream = probe.streams.iter()
+        .find(|s| s.codec_type.as_deref() == Some("audio"))
+        .expect("should have an audio stream");
+    assert_eq!(
+      audio_stream.codec_name.as_deref(),
+      Some("aac"),
+      "expected AAC audio, got {:?}",
+      audio_stream.codec_name,
+    );
+
+    // Sanity-check that the video has non-zero dimensions / duration.
+    assert!(video_stream.width.unwrap_or(0) > 0, "video should have width > 0");
+    assert!(video_stream.height.unwrap_or(0) > 0, "video should have height > 0");
+  }
+}
diff --git a/crates/lib/ffmpeg_utils/src/ffmpeg/mod.rs b/crates/lib/ffmpeg_utils/src/ffmpeg/mod.rs
index ce074120e0..f4632b860d 100644
--- a/crates/lib/ffmpeg_utils/src/ffmpeg/mod.rs
+++ b/crates/lib/ffmpeg_utils/src/ffmpeg/mod.rs
@@ -1,4 +1,5 @@
 pub mod ffmpeg_timestamp_from_duration;
+pub mod ffmpeg_transcode_to_mp4;
 pub mod ffmpeg_trim_and_resample;
 pub mod ffmpeg_video_first_frame_to_jpg_thumbnail;
 pub mod ffmpeg_video_gif_preview;