feat(pipeline): master/proxy transcode arg builder (content pipeline §3.4/§6)

tests/test_pipeline_ffmpeg_ops.py

@@ -1,4 +1,4 @@
-from tools.pipeline.ffmpeg_ops import frame_args, crossfade_loop_args
+from tools.pipeline.ffmpeg_ops import frame_args, crossfade_loop_args, transcode_args
 
 
 def test_frame_args_trims_scales_pads_and_strips_audio():
@@ -33,3 +33,16 @@ def test_crossfade_loop_rejects_overlap_too_large():
     import pytest
     with pytest.raises(ValueError):
         crossfade_loop_args("in.mp4", "loop.mp4", duration=4.0, overlap=2.0)
+
+
+def test_transcode_args_high_profile_even_dims_faststart():
+    args = transcode_args("loop.mp4", "proxy.mp4", width=1920, height=1080,
+                          crf=20, fps=30)
+    assert "-profile:v" in args and args[args.index("-profile:v") + 1] == "high"
+    assert "-crf" in args and args[args.index("-crf") + 1] == "20"
+    vf = args[args.index("-vf") + 1]
+    assert "scale=1920:1080:force_original_aspect_ratio=decrease" in vf
+    assert "fps=30" in vf
+    assert "+faststart" in args
+    assert "-an" in args
+    assert args[-1] == "proxy.mp4"

tools/pipeline/ffmpeg_ops.py

@@ -51,3 +51,21 @@ def crossfade_loop_args(src, dst, *, duration: float, overlap: float,
         "-c:v", "libx264", "-preset", "medium", "-crf", "16",
         "-pix_fmt", "yuv420p", "-movflags", "+faststart", str(dst),
     ]
+
+
+def transcode_args(src, dst, *, width: int, height: int, crf: int,
+                   fps: int = 30, ff: str = "ffmpeg") -> list[str]:
+    """Stage 4 — encode a final deliverable (master or proxy). Master: source res
+    capped ~3840 wide, crf 18. Proxy: 1920×1080, crf 20. Both H.264 High, yuv420p,
+    even dims, +faststart, video-only (spec §6)."""
+    vf = (
+        f"scale={width}:{height}:force_original_aspect_ratio=decrease,"
+        f"pad={width}:{height}:(ow-iw)/2:(oh-ih)/2,"
+        f"setsar=1,fps={fps},format=yuv420p"
+    )
+    return [
+        ff, "-y", "-i", str(src), "-vf", vf, "-an",
+        "-c:v", "libx264", "-profile:v", "high", "-preset", "slow",
+        "-crf", str(crf), "-pix_fmt", "yuv420p",
+        "-movflags", "+faststart", str(dst),
+    ]