feat(music-lab): 다중 트랙 컴파일 백엔드 (FFmpeg concat+crossfade → MP4)

- db.py: compile_jobs 테이블 추가 + CRUD 5종 (create/get/list/update/delete)
- compiler.py: acrossfade 필터 체인 + 그라디언트 배경 + MP4 렌더링 워커
- main.py: /api/music/compile POST·GET·DELETE + /api/music/compiles GET + /api/music/compile/{id}/export GET

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

music-lab/app/compiler.py

@@ -0,0 +1,121 @@
+import os
+import subprocess
+
+from .db import get_compile_job, get_track_file_path, get_track_by_id, update_compile_job
+
+VIDEO_DATA_DIR = os.getenv("VIDEO_DATA_DIR", "/app/data/videos")
+
+
+def _build_concat_cmd(file_paths: list[str], crossfade_sec: float, output_path: str) -> list:
+    """FFmpeg command: N audio files → single audio with acrossfade."""
+    n = len(file_paths)
+    if n == 1:
+        # Single track: just copy
+        return ["ffmpeg", "-y", "-i", file_paths[0], "-c:a", "libmp3lame", "-q:a", "2", output_path]
+
+    cmd = []
+    for fp in file_paths:
+        cmd += ["-i", fp]
+
+    # Build acrossfade filter chain
+    filter_parts = []
+    prev = "0"
+    for i in range(1, n):
+        out_label = f"a{i:02d}"
+        filter_parts.append(f"[{prev}][{i}]acrossfade=d={crossfade_sec}:c1=tri:c2=tri[{out_label}]")
+        prev = out_label
+
+    filter_str = ";".join(filter_parts)
+
+    return (
+        ["ffmpeg", "-y"]
+        + cmd
+        + ["-filter_complex", filter_str, "-map", f"[{prev}]", "-c:a", "libmp3lame", "-q:a", "2", output_path]
+    )
+
+
+def _make_gradient_bg(width: int, height: int, output_path: str) -> None:
+    """Simple dark gradient background image via FFmpeg."""
+    subprocess.run(
+        [
+            "ffmpeg", "-y",
+            "-f", "lavfi",
+            "-i", f"color=c=0x111827:size={width}x{height}:rate=1",
+            "-frames:v", "1",
+            output_path,
+        ],
+        check=True, capture_output=True,
+    )
+
+
+def _get_audio_duration(path: str) -> float:
+    """Return duration in seconds via ffprobe."""
+    try:
+        result = subprocess.run(
+            ["ffprobe", "-v", "error", "-show_entries", "format=duration",
+             "-of", "default=noprint_wrappers=1:nokey=1", path],
+            capture_output=True, text=True, check=True,
+        )
+        return float(result.stdout.strip())
+    except Exception:
+        return 0.0
+
+
+def run_compile(job_id: int) -> None:
+    """Main compile worker — called as BackgroundTask."""
+    job = get_compile_job(job_id)
+    if not job:
+        return
+
+    update_compile_job(job_id, status="rendering")
+
+    try:
+        track_ids = job["track_ids"]
+        if not track_ids:
+            raise ValueError("트랙이 선택되지 않았습니다")
+
+        # Resolve file paths
+        file_paths = []
+        for tid in track_ids:
+            fp = get_track_file_path(tid)
+            if not fp or not os.path.exists(fp):
+                raise ValueError(f"트랙 파일 없음 (id={tid})")
+            file_paths.append(fp)
+
+        out_dir = os.path.join(VIDEO_DATA_DIR, f"compile_{job_id}")
+        os.makedirs(out_dir, exist_ok=True)
+
+        # Step 1: concat audio
+        audio_path = os.path.join(out_dir, "audio.mp3")
+        concat_cmd = _build_concat_cmd(file_paths, job["crossfade_sec"], audio_path)
+        subprocess.run(concat_cmd, check=True, capture_output=True)
+
+        duration = _get_audio_duration(audio_path)
+
+        # Step 2: background image
+        bg_path = os.path.join(out_dir, "bg.jpg")
+        _make_gradient_bg(1920, 1080, bg_path)
+
+        # Step 3: audio + bg → MP4
+        output_path = os.path.join(out_dir, "output.mp4")
+        subprocess.run(
+            [
+                "ffmpeg", "-y",
+                "-loop", "1", "-i", bg_path,
+                "-i", audio_path,
+                "-c:v", "libx264", "-tune", "stillimage", "-preset", "fast",
+                "-c:a", "aac", "-b:a", "192k",
+                "-pix_fmt", "yuv420p",
+                "-shortest",
+                output_path,
+            ],
+            check=True, capture_output=True,
+        )
+
+        update_compile_job(job_id, status="done", output_path=output_path, duration_sec=duration)
+
+    except subprocess.CalledProcessError as e:
+        err = (e.stderr or b"").decode()[-300:]
+        update_compile_job(job_id, status="failed", error=err)
+    except Exception as e:
+        update_compile_job(job_id, status="failed", error=str(e))

music-lab/app/db.py

@@ -169,6 +169,21 @@ def init_db() -> None:
             )
         """)
 
+        # ── compile_jobs 테이블 ───────────────────────────────────────────
+        conn.execute("""
+            CREATE TABLE IF NOT EXISTS compile_jobs (
+                id            INTEGER PRIMARY KEY AUTOINCREMENT,
+                title         TEXT    NOT NULL DEFAULT '',
+                track_ids     TEXT    NOT NULL DEFAULT '[]',
+                crossfade_sec REAL    NOT NULL DEFAULT 3.0,
+                status        TEXT    NOT NULL DEFAULT 'pending',
+                output_path   TEXT,
+                duration_sec  REAL,
+                error         TEXT,
+                created_at    TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now'))
+            )
+        """)
+
 
 # ── music_tasks CRUD ──────────────────────────────────────────────────────────
 
@@ -707,3 +722,72 @@ def get_trend_reports(limit: int = 10) -> list:
         }
         for r in rows
     ]
+
+
+# ── Compile Jobs ─────────────────────────────────────────
+
+def create_compile_job(title: str, track_ids: list, crossfade_sec: float) -> int:
+    with _conn() as conn:
+        cur = conn.execute(
+            "INSERT INTO compile_jobs (title, track_ids, crossfade_sec) VALUES (?,?,?)",
+            (title, json.dumps(track_ids), crossfade_sec),
+        )
+        return cur.lastrowid
+
+
+def get_compile_jobs() -> list:
+    with _conn() as conn:
+        rows = conn.execute(
+            "SELECT id, title, track_ids, crossfade_sec, status, duration_sec, created_at "
+            "FROM compile_jobs ORDER BY created_at DESC LIMIT 50"
+        ).fetchall()
+    return [
+        {
+            "id":            r["id"],
+            "title":         r["title"],
+            "track_ids":     json.loads(r["track_ids"]),
+            "crossfade_sec": r["crossfade_sec"],
+            "status":        r["status"],
+            "duration_sec":  r["duration_sec"],
+            "created_at":    r["created_at"],
+        }
+        for r in rows
+    ]
+
+
+def get_compile_job(job_id: int) -> Optional[Dict[str, Any]]:
+    with _conn() as conn:
+        r = conn.execute(
+            "SELECT * FROM compile_jobs WHERE id = ?", (job_id,)
+        ).fetchone()
+    if not r:
+        return None
+    return {
+        "id":            r["id"],
+        "title":         r["title"],
+        "track_ids":     json.loads(r["track_ids"]),
+        "crossfade_sec": r["crossfade_sec"],
+        "status":        r["status"],
+        "output_path":   r["output_path"],
+        "duration_sec":  r["duration_sec"],
+        "error":         r["error"],
+        "created_at":    r["created_at"],
+    }
+
+
+def update_compile_job(job_id: int, **kwargs) -> None:
+    allowed = {"status", "output_path", "duration_sec", "error"}
+    fields = {k: v for k, v in kwargs.items() if k in allowed}
+    if not fields:
+        return
+    set_clause = ", ".join(f"{k} = ?" for k in fields)
+    with _conn() as conn:
+        conn.execute(
+            f"UPDATE compile_jobs SET {set_clause} WHERE id = ?",
+            (*fields.values(), job_id),
+        )
+
+
+def delete_compile_job(job_id: int) -> None:
+    with _conn() as conn:
+        conn.execute("DELETE FROM compile_jobs WHERE id = ?", (job_id,))

music-lab/app/main.py

@@ -19,7 +19,10 @@ from .db import (
     update_revenue_record, delete_revenue_record, get_revenue_dashboard,
     get_market_trends as _get_market_trends,
     get_latest_trend_report, get_trend_reports as _get_trend_reports,
+    create_compile_job, get_compile_jobs, get_compile_job,
+    update_compile_job, delete_compile_job,
 )
+from .compiler import run_compile
 from .market import ingest_trends, get_suggestions
 from .local_provider import run_local_generation
 from .suno_provider import (
@@ -783,6 +786,66 @@ def delete_project(project_id: int):
     return {"ok": True}
 
 
+# ── Compile Jobs ──────────────────────────────────────────────────────────────
+
+class CompileRequest(BaseModel):
+    title: str = ""
+    track_ids: list[int]
+    crossfade_sec: float = 3.0
+
+
+@app.post("/api/music/compile")
+def create_compile(req: CompileRequest, background_tasks: BackgroundTasks):
+    if not req.track_ids:
+        raise HTTPException(status_code=400, detail="track_ids 필수")
+    if not (0.5 <= req.crossfade_sec <= 15):
+        raise HTTPException(status_code=400, detail="crossfade_sec: 0.5~15")
+    job_id = create_compile_job(req.title, req.track_ids, req.crossfade_sec)
+    background_tasks.add_task(run_compile, job_id)
+    return {"id": job_id, "status": "rendering"}
+
+
+@app.get("/api/music/compiles")
+def list_compiles():
+    return {"jobs": get_compile_jobs()}
+
+
+@app.get("/api/music/compile/{job_id}")
+def get_compile(job_id: int):
+    job = get_compile_job(job_id)
+    if not job:
+        raise HTTPException(status_code=404, detail="Not found")
+    return job
+
+
+@app.delete("/api/music/compile/{job_id}")
+def delete_compile(job_id: int):
+    job = get_compile_job(job_id)
+    if not job:
+        raise HTTPException(status_code=404, detail="Not found")
+    if job.get("output_path"):
+        out_dir = os.path.dirname(job["output_path"])
+        if os.path.exists(out_dir):
+            shutil.rmtree(out_dir, ignore_errors=True)
+    delete_compile_job(job_id)
+    return {"ok": True}
+
+
+@app.get("/api/music/compile/{job_id}/export")
+def export_compile(job_id: int):
+    job = get_compile_job(job_id)
+    if not job or job["status"] != "done":
+        raise HTTPException(status_code=404, detail="Not ready")
+    out_dir = os.path.dirname(job["output_path"])
+    rel = os.path.relpath(job["output_path"], os.getenv("VIDEO_DATA_DIR", "/app/data/videos"))
+    mp4_url = f"/media/videos/{rel}"
+    return {
+        "mp4_url":      mp4_url,
+        "duration_sec": job["duration_sec"],
+        "title":        job["title"],
+    }
+
+
 # ── 수익화 추적 API ───────────────────────────────────────────────────────────
 
 @app.get("/api/music/revenue/dashboard")