Add video stream copy remuxing

tools/video_encode_output.py

@@ -168,6 +168,60 @@ def render_audio_wav(
         )
 
 
+def remux_video(
+    *,
+    ffmpeg: Path,
+    source: Path,
+    audio_source: Path | None,
+    output: Path,
+    audio_options: AudioEncodeOptions,
+    source_has_audio: bool,
+    frame_count: int | None = None,
+    progress_label: str | None = None,
+) -> VideoEncodeResult:
+    """Copy the source video stream while optionally copying or encoding audio."""
+    output.parent.mkdir(parents=True, exist_ok=True)
+    command = [
+        str(ffmpeg), "-y", "-hide_banner", "-loglevel", "info", "-nostats",
+        "-progress", "pipe:2", "-i", str(source), "-map", "0:v:0", "-c:v", "copy",
+    ]
+    if audio_options.mode == "none" or not source_has_audio:
+        command.append("-an")
+    else:
+        source_index = 0
+        if audio_source is not None and audio_source.resolve() != source.resolve():
+            command.extend(["-i", str(audio_source)])
+            source_index = 1
+        command.extend(["-map", f"{source_index}:a:0"])
+        if audio_options.mode == "copy":
+            command.extend(["-c:a", "copy"])
+        else:
+            add_audio_encoder_options(command, audio_options)
+    command.append(str(output))
+    process = subprocess.Popen(
+        command,
+        stdout=subprocess.DEVNULL,
+        stderr=subprocess.PIPE,
+        text=True,
+    )
+    encoder_log = read_ffmpeg_progress(
+        process,
+        total_frames=frame_count,
+        label=f"Remuxing {progress_label or output.name}",
+    )
+    if process.returncode != 0:
+        raise RuntimeError(
+            f"FFmpeg remux failed for {source} with exit {process.returncode}:\n{encoder_log}"
+        )
+    return VideoEncodeResult(
+        script=source,
+        output=output,
+        renderer_returncode=0,
+        ffmpeg_returncode=process.returncode,
+        encoder_log=encoder_log,
+    )
+
+
 def encode_video_only_y4m(
     *,
     y4m_command: list[str],