feat: FFmpeg video composition pipeline — shared infra (#643)

Shared video pipeline for Video Forge (#53) and LPM 1.0 (#641).

tools/video_pipeline.py:
- FFmpegPipeline class wrapping ffmpeg CLI
- Image sequence -> video with crossfade transitions
- Ken Burns pan/zoom effect on still images
- Audio-video muxing with beat alignment
- H.264/WebM encoding with faststart for web
- HLS streaming output
- Full compose() pipeline combining all components

tests/test_video_pipeline.py: 14 tests

Closes #643

tests/test_video_pipeline.py

@@ -0,0 +1,129 @@
+"""Tests for FFmpeg Video Composition Pipeline — Issue #643."""
+
+import os
+import pytest
+import tempfile
+from unittest.mock import patch, MagicMock
+
+from tools.video_pipeline import (
+    VideoSpec, Transition, KenBurnsConfig,
+    FFmpegPipeline, compose_video,
+)
+
+
+class TestVideoSpec:
+    def test_defaults(self):
+        s = VideoSpec()
+        assert s.width == 1920
+        assert s.height == 1080
+        assert s.fps == 30
+        assert s.codec == "libx264"
+        assert s.container == "mp4"
+        assert s.crf == 23
+
+    def test_webm_spec(self):
+        s = VideoSpec(codec="libvpx-vp9", container="webm", audio_codec="libopus")
+        assert s.container == "webm"
+        assert s.codec == "libvpx-vp9"
+
+
+class TestTransition:
+    def test_defaults(self):
+        t = Transition()
+        assert t.duration_sec == 1.0
+        assert t.type == "fade"
+
+
+class TestKenBurnsConfig:
+    def test_defaults(self):
+        k = KenBurnsConfig()
+        assert k.zoom_start == 1.0
+        assert k.zoom_end == 1.15
+        assert k.duration_sec == 5.0
+
+
+class TestFFmpegPipelineInit:
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_verify_ffmpeg_passes(self, mock_run):
+        mock_run.return_value = MagicMock(returncode=0, stdout="ffmpeg version 6.0")
+        pipeline = FFmpegPipeline()
+        assert pipeline.ffmpeg == "ffmpeg"
+
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_verify_ffmpeg_fails(self, mock_run):
+        mock_run.side_effect = FileNotFoundError()
+        with pytest.raises(RuntimeError, match="FFmpeg not found"):
+            FFmpegPipeline()
+
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_custom_ffmpeg_path(self, mock_run):
+        mock_run.return_value = MagicMock(returncode=0, stdout="ffmpeg")
+        pipeline = FFmpegPipeline(ffmpeg_path="/usr/local/bin/ffmpeg")
+        assert pipeline.ffmpeg == "/usr/local/bin/ffmpeg"
+
+
+class TestFFmpegPipelineProbe:
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_probe_returns_metadata(self, mock_run):
+        mock_run.return_value = MagicMock(
+            returncode=0,
+            stdout='{"format": {"duration": "10.5"}, "streams": []}'
+        )
+        pipeline = FFmpegPipeline.__new__(FFmpegPipeline)
+        pipeline.ffprobe = "ffprobe"
+        result = pipeline.probe("/tmp/test.mp4")
+        assert result["format"]["duration"] == "10.5"
+
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_get_duration(self, mock_run):
+        mock_run.return_value = MagicMock(
+            returncode=0,
+            stdout='{"format": {"duration": "42.3"}, "streams": []}'
+        )
+        pipeline = FFmpegPipeline.__new__(FFmpegPipeline)
+        pipeline.ffprobe = "ffprobe"
+        assert pipeline.get_duration("/tmp/test.mp4") == 42.3
+
+
+class TestFFmpegPipelineImagesToVideo:
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_empty_images_raises(self, mock_run):
+        pipeline = FFmpegPipeline.__new__(FFmpegPipeline)
+        pipeline.ffmpeg = "ffmpeg"
+        with pytest.raises(ValueError, match="No images"):
+            pipeline.images_to_video([], "/tmp/out.mp4")
+
+
+class TestComposeVideo:
+    @patch("tools.video_pipeline.FFmpegPipeline")
+    def test_compose_calls_pipeline(self, MockPipeline):
+        mock_instance = MagicMock()
+        mock_instance.compose.return_value = "/tmp/output.mp4"
+        MockPipeline.return_value = mock_instance
+        
+        result = compose_video(["img1.png", "img2.png"], output="/tmp/out.mp4")
+        assert result == "/tmp/output.mp4"
+        mock_instance.compose.assert_called_once()
+
+
+class TestRunFFmpeg:
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_success(self, mock_run):
+        mock_run.return_value = MagicMock(returncode=0, stdout="")
+        pipeline = FFmpegPipeline.__new__(FFmpegPipeline)
+        pipeline._run_ffmpeg(["ffmpeg", "-version"])
+
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_failure_raises(self, mock_run):
+        mock_run.return_value = MagicMock(returncode=1, stderr="Error: invalid input")
+        pipeline = FFmpegPipeline.__new__(FFmpegPipeline)
+        with pytest.raises(RuntimeError, match="FFmpeg error"):
+            pipeline._run_ffmpeg(["ffmpeg", "-bad"])
+
+    @patch("tools.video_pipeline.subprocess.run")
+    def test_timeout_raises(self, mock_run):
+        import subprocess
+        mock_run.side_effect = subprocess.TimeoutExpired(cmd="ffmpeg", timeout=600)
+        pipeline = FFmpegPipeline.__new__(FFmpegPipeline)
+        with pytest.raises(subprocess.TimeoutExpired):
+            pipeline._run_ffmpeg(["ffmpeg", "-slow"])

tools/video_pipeline.py

@@ -0,0 +1,571 @@
+"""FFmpeg Video Composition Pipeline — Shared Infrastructure (Issue #643).
+
+Used by both Video Forge (playground #53) and LPM 1.0 (#641).
+
+Provides:
+- Image sequence → video with crossfade transitions
+- Audio-video sync with beat alignment
+- Ken Burns effect (slow pan/zoom on stills)
+- H.264/WebM encoding optimized for web
+- Streaming output support
+
+Dependencies: ffmpeg (system binary), optional ffmpeg-python bindings.
+"""
+
+import json
+import logging
+import os
+import subprocess
+import tempfile
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Dict, List, Optional, Tuple
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class VideoSpec:
+    """Video output specification."""
+    width: int = 1920
+    height: int = 1080
+    fps: int = 30
+    codec: str = "libx264"  # libx264, libvpx-vp9
+    container: str = "mp4"  # mp4, webm
+    crf: int = 23  # quality (lower = better, 18-28 typical)
+    preset: str = "medium"  # ultrafast, fast, medium, slow
+    audio_codec: str = "aac"
+    audio_bitrate: str = "192k"
+
+
+@dataclass
+class Transition:
+    """Crossfade transition between clips."""
+    duration_sec: float = 1.0
+    type: str = "fade"  # fade, dissolve, slideleft, slideright
+
+
+@dataclass
+class KenBurnsConfig:
+    """Ken Burns pan/zoom effect configuration."""
+    zoom_start: float = 1.0
+    zoom_end: float = 1.15
+    pan_x: float = 0.0  # -1 to 1
+    pan_y: float = 0.0  # -1 to 1
+    duration_sec: float = 5.0
+
+
+class FFmpegPipeline:
+    """FFmpeg wrapper for video composition.
+    
+    Provides a Python interface to FFmpeg's complex filter graphs
+    for composing videos from images, clips, and audio.
+    """
+    
+    def __init__(self, ffmpeg_path: str = "ffmpeg", ffprobe_path: str = "ffprobe"):
+        self.ffmpeg = ffmpeg_path
+        self.ffprobe = ffprobe_path
+        self._verify_ffmpeg()
+    
+    def _verify_ffmpeg(self):
+        """Verify FFmpeg is available."""
+        try:
+            r = subprocess.run([self.ffmpeg, "-version"], capture_output=True, text=True, timeout=5)
+            if r.returncode != 0:
+                raise RuntimeError(f"FFmpeg returned {r.returncode}")
+            logger.info("FFmpeg verified: %s", r.stdout.split('\n')[0])
+        except FileNotFoundError:
+            raise RuntimeError(f"FFmpeg not found at '{self.ffmpeg}'. Install: brew install ffmpeg")
+    
+    def probe(self, path: str) -> Dict[str, Any]:
+        """Probe a media file for metadata."""
+        cmd = [
+            self.ffprobe, "-v", "quiet", "-print_format", "json",
+            "-show_format", "-show_streams", path
+        ]
+        r = subprocess.run(cmd, capture_output=True, text=True, timeout=30)
+        if r.returncode != 0:
+            raise RuntimeError(f"ffprobe failed: {r.stderr}")
+        return json.loads(r.stdout)
+    
+    def get_duration(self, path: str) -> float:
+        """Get duration of a media file in seconds."""
+        info = self.probe(path)
+        return float(info["format"]["duration"])
+    
+    # =================================================================
+    # Image Sequence → Video
+    # =================================================================
+    
+    def images_to_video(
+        self,
+        image_paths: List[str],
+        output_path: str,
+        spec: VideoSpec = VideoSpec(),
+        transition: Optional[Transition] = None,
+        image_duration: float = 3.0,
+    ) -> str:
+        """Convert a list of images to a video with optional crossfade transitions.
+        
+        Args:
+            image_paths: List of image file paths
+            output_path: Output video path
+            spec: Video output specification
+            transition: Crossfade config (None = hard cuts)
+            image_duration: Seconds per image
+            
+        Returns:
+            Path to output video
+        """
+        if not image_paths:
+            raise ValueError("No images provided")
+        
+        if transition and len(image_paths) > 1:
+            return self._images_with_crossfade(
+                image_paths, output_path, spec, transition, image_duration
+            )
+        else:
+            return self._images_hard_cut(
+                image_paths, output_path, spec, image_duration
+            )
+    
+    def _images_hard_cut(
+        self,
+        image_paths: List[str],
+        output_path: str,
+        spec: VideoSpec,
+        duration: float,
+    ) -> str:
+        """Simple image sequence with hard cuts."""
+        # Create concat file
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.txt', delete=False) as f:
+            concat_path = f.name
+            for img in image_paths:
+                f.write(f"file '{os.path.abspath(img)}'\n")
+                f.write(f"duration {duration}\n")
+            # Last image needs repeating for ffmpeg concat
+            f.write(f"file '{os.path.abspath(image_paths[-1])}'\n")
+        
+        try:
+            cmd = [
+                self.ffmpeg, "-y", "-f", "concat", "-safe", "0",
+                "-i", concat_path,
+                "-vf", f"scale={spec.width}:{spec.height}:force_original_aspect_ratio=decrease,pad={spec.width}:{spec.height}:(ow-iw)/2:(oh-ih)/2",
+                "-c:v", spec.codec, "-crf", str(spec.crf), "-preset", spec.preset,
+                "-pix_fmt", "yuv420p", "-r", str(spec.fps),
+                output_path
+            ]
+            self._run_ffmpeg(cmd)
+            return output_path
+        finally:
+            os.unlink(concat_path)
+    
+    def _images_with_crossfade(
+        self,
+        image_paths: List[str],
+        output_path: str,
+        spec: VideoSpec,
+        transition: Transition,
+        duration: float,
+    ) -> str:
+        """Image sequence with xfade crossfade transitions."""
+        n = len(image_paths)
+        fade_dur = transition.duration_sec
+        clip_dur = duration
+        
+        # Build filter complex
+        inputs = []
+        for img in image_paths:
+            inputs.extend(["-loop", "1", "-t", str(clip_dur), "-i", img])
+        
+        # Scale all inputs
+        filter_parts = []
+        for i in range(n):
+            filter_parts.append(
+                f"[{i}:v]scale={spec.width}:{spec.height}:force_original_aspect_ratio=decrease,"
+                f"pad={spec.width}:{spec.height}:(ow-iw)/2:(oh-ih)/2,setsar=1,fps={spec.fps}[v{i}]"
+            )
+        
+        # Chain xfade transitions
+        if n == 1:
+            filter_parts.append(f"[v0]copy[outv]")
+        else:
+            offset = clip_dur - fade_dur
+            filter_parts.append(f"[v0][v1]xfade=transition={transition.type}:duration={fade_dur}:offset={offset}[xf0]")
+            for i in range(1, n - 1):
+                offset = (i + 1) * clip_dur - (i + 1) * fade_dur
+                filter_parts.append(f"[xf{i-1}][v{i+1}]xfade=transition={transition.type}:duration={fade_dur}:offset={offset}[xf{i}]")
+            filter_parts.append(f"[xf{n-2}]copy[outv]")
+        
+        filter_complex = ";\n".join(filter_parts)
+        
+        cmd = [
+            self.ffmpeg, "-y",
+            *inputs,
+            "-filter_complex", filter_complex,
+            "-map", "[outv]",
+            "-c:v", spec.codec, "-crf", str(spec.crf), "-preset", spec.preset,
+            "-pix_fmt", "yuv420p",
+            output_path
+        ]
+        self._run_ffmpeg(cmd)
+        return output_path
+    
+    # =================================================================
+    # Ken Burns Effect
+    # =================================================================
+    
+    def apply_ken_burns(
+        self,
+        image_path: str,
+        output_path: str,
+        config: KenBurnsConfig = KenBurnsConfig(),
+        spec: VideoSpec = VideoSpec(),
+    ) -> str:
+        """Apply Ken Burns (pan + zoom) effect to a still image.
+        
+        Creates a video from a single image with slow zoom and pan motion.
+        """
+        # zoompan filter: z=zoom, x/y=pan position
+        # z goes from zoom_start to zoom_end over the duration
+        total_frames = int(config.duration_sec * spec.fps)
+        
+        zoom_expr = f"min({config.zoom_start}+on*({config.zoom_zoom_end}-{config.zoom_start})/{total_frames},{config.zoom_end})"
+        
+        # Pan expression: move from center ± pan offset
+        x_expr = f"(iw-iw/zoom)/2+{config.pan_x}*iw*0.1*(on/{total_frames})"
+        y_expr = f"(ih-ih/zoom)/2+{config.pan_y}*ih*0.1*(on/{total_frames})"
+        
+        filter_str = (
+            f"zoompan=z='min(zoom+0.001,{config.zoom_end})'"
+            f":x='iw/2-(iw/zoom/2)+{config.pan_x}*10'"
+            f":y='ih/2-(ih/zoom/2)+{config.pan_y}*10'"
+            f":d={total_frames}:s={spec.width}x{spec.height}:fps={spec.fps}"
+        )
+        
+        cmd = [
+            self.ffmpeg, "-y",
+            "-loop", "1", "-i", image_path,
+            "-vf", filter_str,
+            "-t", str(config.duration_sec),
+            "-c:v", spec.codec, "-crf", str(spec.crf), "-preset", spec.preset,
+            "-pix_fmt", "yuv420p",
+            output_path
+        ]
+        self._run_ffmpeg(cmd)
+        return output_path
+    
+    # =================================================================
+    # Audio-Video Sync
+    # =================================================================
+    
+    def mux_audio_video(
+        self,
+        video_path: str,
+        audio_path: str,
+        output_path: str,
+        spec: VideoSpec = VideoSpec(),
+        offset_sec: float = 0.0,
+    ) -> str:
+        """Mux audio and video together with optional offset.
+        
+        Args:
+            video_path: Video file path
+            audio_path: Audio file path
+            output_path: Output path
+            spec: Output spec
+            offset_sec: Audio offset in seconds (positive = delay audio)
+        """
+        cmd = [
+            self.ffmpeg, "-y",
+            "-i", video_path,
+            "-i", audio_path,
+        ]
+        
+        if offset_sec > 0:
+            cmd.extend(["-itsoffset", str(offset_sec), "-i", audio_path])
+            cmd.extend(["-map", "0:v", "-map", "2:a"])
+        elif offset_sec < 0:
+            cmd.extend(["-itsoffset", str(-offset_sec), "-i", video_path])
+            cmd.extend(["-map", "2:v", "-map", "1:a"])
+        else:
+            cmd.extend(["-map", "0:v", "-map", "1:a"])
+        
+        cmd.extend([
+            "-c:v", "copy",
+            "-c:a", spec.audio_codec, "-b:a", spec.audio_bitrate,
+            "-shortest",
+            output_path
+        ])
+        self._run_ffmpeg(cmd)
+        return output_path
+    
+    def align_to_beats(
+        self,
+        video_path: str,
+        audio_path: str,
+        beat_times: List[float],
+        output_path: str,
+        spec: VideoSpec = VideoSpec(),
+    ) -> str:
+        """Align video cuts to audio beat times.
+        
+        Splits video at beat timestamps and reassembles with audio sync.
+        """
+        if not beat_times:
+            return self.mux_audio_video(video_path, audio_path, output_path, spec)
+        
+        video_dur = self.get_duration(video_path)
+        
+        # Build segment list based on beat times
+        segments = []
+        prev = 0.0
+        for beat in beat_times:
+            if beat > prev and beat <= video_dur:
+                segments.append((prev, beat))
+                prev = beat
+        if prev < video_dur:
+            segments.append((prev, video_dur))
+        
+        # Extract segments
+        segment_paths = []
+        with tempfile.TemporaryDirectory() as tmpdir:
+            for i, (start, end) in enumerate(segments):
+                seg_path = os.path.join(tmpdir, f"seg_{i:04d}.ts")
+                cmd = [
+                    self.ffmpeg, "-y", "-ss", str(start), "-i", video_path,
+                    "-t", str(end - start), "-c", "copy", seg_path
+                ]
+                self._run_ffmpeg(cmd)
+                segment_paths.append(seg_path)
+            
+            # Concat segments
+            concat_path = os.path.join(tmpdir, "concat.txt")
+            with open(concat_path, "w") as f:
+                for sp in segment_paths:
+                    f.write(f"file '{sp}'\n")
+            
+            cmd = [
+                self.ffmpeg, "-y", "-f", "concat", "-safe", "0",
+                "-i", concat_path, "-c", "copy",
+                os.path.join(tmpdir, "video_aligned.mp4")
+            ]
+            self._run_ffmpeg(cmd)
+            
+            return self.mux_audio_video(
+                os.path.join(tmpdir, "video_aligned.mp4"),
+                audio_path, output_path, spec
+            )
+    
+    # =================================================================
+    # Encoding
+    # =================================================================
+    
+    def encode_web(
+        self,
+        input_path: str,
+        output_path: str,
+        spec: VideoSpec = VideoSpec(),
+    ) -> str:
+        """Encode for web playback (H.264 MP4 or WebM)."""
+        if spec.container == "webm":
+            cmd = [
+                self.ffmpeg, "-y", "-i", input_path,
+                "-c:v", "libvpx-vp9", "-crf", str(spec.crf), "-b:v", "0",
+                "-c:a", "libopus", "-b:a", spec.audio_bitrate,
+                "-pix_fmt", "yuv420p",
+                output_path
+            ]
+        else:
+            cmd = [
+                self.ffmpeg, "-y", "-i", input_path,
+                "-c:v", spec.codec, "-crf", str(spec.crf), "-preset", spec.preset,
+                "-c:a", spec.audio_codec, "-b:a", spec.audio_bitrate,
+                "-movflags", "+faststart",  # Progressive download
+                "-pix_fmt", "yuv420p",
+                output_path
+            ]
+        self._run_ffmpeg(cmd)
+        return output_path
+    
+    # =================================================================
+    # Full Composition Pipeline
+    # =================================================================
+    
+    def compose(
+        self,
+        images: List[str],
+        audio: Optional[str] = None,
+        output_path: str = "output.mp4",
+        spec: VideoSpec = VideoSpec(),
+        transition: Optional[Transition] = None,
+        ken_burns: Optional[KenBurnsConfig] = None,
+        beat_times: Optional[List[float]] = None,
+    ) -> str:
+        """Full composition pipeline: images → video → mux audio → encode.
+        
+        This is the main entry point. Combines all pipeline components
+        into a single call.
+        
+        Args:
+            images: List of image paths
+            audio: Optional audio file path
+            output_path: Final output path
+            spec: Video specification
+            transition: Crossfade config
+            ken_burns: Ken Burns config (applied to each image before composition)
+            beat_times: Beat timestamps for audio-visual sync
+            
+        Returns:
+            Path to final video
+        """
+        with tempfile.TemporaryDirectory() as tmpdir:
+            # Apply Ken Burns to each image if configured
+            processed_images = images
+            if ken_burns:
+                processed_images = []
+                for i, img in enumerate(images):
+                    kb_path = os.path.join(tmpdir, f"kb_{i:04d}.mp4")
+                    self.apply_ken_burns(img, kb_path, ken_burns, spec)
+                    processed_images.append(kb_path)
+            
+            # Compose images into video
+            video_path = os.path.join(tmpdir, "composed.mp4")
+            if processed_images and all(p.endswith('.mp4') for p in processed_images):
+                # All Ken Burns clips — concat them
+                self._concat_videos(processed_images, video_path, transition, spec)
+            else:
+                self.images_to_video(processed_images, video_path, spec, transition)
+            
+            # Mux audio if provided
+            if audio:
+                if beat_times:
+                    return self.align_to_beats(video_path, audio, beat_times, output_path, spec)
+                else:
+                    return self.mux_audio_video(video_path, audio, output_path, spec)
+            else:
+                # Just copy the video
+                import shutil
+                shutil.copy2(video_path, output_path)
+                return output_path
+    
+    def _concat_videos(
+        self,
+        video_paths: List[str],
+        output_path: str,
+        transition: Optional[Transition],
+        spec: VideoSpec,
+    ) -> str:
+        """Concatenate video files with optional transitions."""
+        if not transition:
+            with tempfile.NamedTemporaryFile(mode='w', suffix='.txt', delete=False) as f:
+                concat_path = f.name
+                for vp in video_paths:
+                    f.write(f"file '{os.path.abspath(vp)}'\n")
+            try:
+                cmd = [
+                    self.ffmpeg, "-y", "-f", "concat", "-safe", "0",
+                    "-i", concat_path, "-c", "copy", output_path
+                ]
+                self._run_ffmpeg(cmd)
+            finally:
+                os.unlink(concat_path)
+        else:
+            # Use xfade for video clips too
+            n = len(video_paths)
+            inputs = []
+            for vp in video_paths:
+                inputs.extend(["-i", vp])
+            
+            filter_parts = []
+            for i in range(n):
+                filter_parts.append(f"[{i}:v]fps={spec.fps},scale={spec.width}:{spec.height}[v{i}]")
+            
+            fade_dur = transition.duration_sec
+            # Calculate offsets from durations
+            if n >= 2:
+                dur0 = self.get_duration(video_paths[0])
+                offset = dur0 - fade_dur
+                filter_parts.append(f"[v0][v1]xfade=transition={transition.type}:duration={fade_dur}:offset={offset}[xf0]")
+                for i in range(1, n - 1):
+                    duri = self.get_duration(video_paths[i])
+                    offset += duri - fade_dur
+                    filter_parts.append(f"[xf{i-1}][v{i+1}]xfade=transition={transition.type}:duration={fade_dur}:offset={offset}[xf{i}]")
+                filter_parts.append(f"[xf{n-2}]copy[outv]")
+            else:
+                filter_parts.append(f"[v0]copy[outv]")
+            
+            cmd = [
+                self.ffmpeg, "-y", *inputs,
+                "-filter_complex", ";".join(filter_parts),
+                "-map", "[outv]",
+                "-c:v", spec.codec, "-crf", str(spec.crf), "-preset", spec.preset,
+                output_path
+            ]
+            self._run_ffmpeg(cmd)
+        return output_path
+    
+    # =================================================================
+    # Streaming
+    # =================================================================
+    
+    def create_hls_stream(
+        self,
+        input_path: str,
+        output_dir: str,
+        segment_duration: int = 4,
+    ) -> str:
+        """Create HLS streaming output for progressive playback.
+        
+        Returns:
+            Path to the .m3u8 playlist file
+        """
+        os.makedirs(output_dir, exist_ok=True)
+        playlist = os.path.join(output_dir, "playlist.m3u8")
+        
+        cmd = [
+            self.ffmpeg, "-y", "-i", input_path,
+            "-c:v", "libx264", "-crf", "23", "-preset", "fast",
+            "-c:a", "aac", "-b:a", "128k",
+            "-f", "hls", "-hls_time", str(segment_duration),
+            "-hls_list_size", "0", "-hls_segment_filename",
+            os.path.join(output_dir, "seg_%03d.ts"),
+            playlist
+        ]
+        self._run_ffmpeg(cmd)
+        return playlist
+    
+    # =================================================================
+    # Internal
+    # =================================================================
+    
+    def _run_ffmpeg(self, cmd: List[str], timeout: int = 600):
+        """Run an FFmpeg command with logging and error handling."""
+        logger.info("FFmpeg: %s", " ".join(cmd[:8]) + "...")
+        r = subprocess.run(cmd, capture_output=True, text=True, timeout=timeout)
+        if r.returncode != 0:
+            logger.error("FFmpeg failed: %s", r.stderr[-500:])
+            raise RuntimeError(f"FFmpeg error (exit {r.returncode}): {r.stderr[-500:]}")
+        return r.stdout
+
+
+# =========================================================================
+# Convenience functions
+# =========================================================================
+
+def compose_video(
+    images: List[str],
+    audio: Optional[str] = None,
+    output: str = "output.mp4",
+    **kwargs,
+) -> str:
+    """One-call video composition from images and optional audio.
+    
+    Convenience wrapper around FFmpegPipeline.compose().
+    """
+    pipeline = FFmpegPipeline()
+    spec = kwargs.pop("spec", VideoSpec())
+    transition = kwargs.pop("transition", None)
+    ken_burns = kwargs.pop("ken_burns", None)
+    beat_times = kwargs.pop("beat_times", None)
+    return pipeline.compose(images, audio, output, spec, transition, ken_burns, beat_times)