feat: per-join crossfade durations + acrossfade curve in build_crossfade_merge_command

tests/test_utils.py

@@ -139,6 +139,58 @@ def test_merge_empty_raises():
     with pytest.raises(ValueError):
         build_crossfade_merge_command([], 0.5, "/o/o.wav")
 
+def test_merge_per_join_crossfades():
+    cmd = build_crossfade_merge_command(["/a.wav", "/b.wav", "/c.wav"], [0.5, 1.5], "/o/o.wav")
+    fc = cmd[cmd.index("-filter_complex") + 1]
+    assert "[0][1]acrossfade=d=0.5[a1]" in fc
+    assert "[a1][2]acrossfade=d=1.5[out]" in fc
+
+def test_merge_curve_emitted_when_non_default():
+    cmd = build_crossfade_merge_command(["/a.wav", "/b.wav"], 0.5, "/o/o.wav", curves="exp")
+    fc = cmd[cmd.index("-filter_complex") + 1]
+    assert "acrossfade=d=0.5:c1=exp:c2=exp[out]" in fc
+
+def test_merge_default_curve_omits_c1c2():
+    cmd = build_crossfade_merge_command(["/a.wav", "/b.wav"], 0.5, "/o/o.wav")   # tri default
+    fc = cmd[cmd.index("-filter_complex") + 1]
+    assert "c1=" not in fc                      # tri is ffmpeg's default -> omit
+
+def test_merge_per_join_curves_list():
+    cmd = build_crossfade_merge_command(["/a.wav", "/b.wav", "/c.wav"], 0.5, "/o/o.wav",
+                                        curves=["tri", "exp"])
+    fc = cmd[cmd.index("-filter_complex") + 1]
+    assert "[0][1]acrossfade=d=0.5[a1]" in fc                 # tri -> no suffix
+    assert "acrossfade=d=0.5:c1=exp:c2=exp[out]" in fc        # exp on 2nd join
+
+def test_merge_mixed_zero_crossfade():
+    cmd = build_crossfade_merge_command(["/a.wav", "/b.wav", "/c.wav"], [0.0, 0.5], "/o/o.wav")
+    fc = cmd[cmd.index("-filter_complex") + 1]
+    assert "[0][1]concat=n=2:v=0:a=1[a1]" in fc               # butt-join 1st
+    assert "acrossfade=d=0.5" in fc                           # crossfade 2nd
+
+def test_merge_crossfade_list_length_mismatch_raises():
+    import pytest
+    with pytest.raises(ValueError):
+        build_crossfade_merge_command(["/a.wav", "/b.wav", "/c.wav"], [0.5], "/o/o.wav")
+    with pytest.raises(ValueError):
+        build_crossfade_merge_command(["/a.wav", "/b.wav"], [0.5, 0.5], "/o/o.wav")
+
+def test_merge_curves_list_length_mismatch_raises():
+    import pytest
+    with pytest.raises(ValueError):
+        build_crossfade_merge_command(["/a.wav", "/b.wav", "/c.wav"], 0.5, "/o/o.wav", curves=["exp"])
+
+def test_merge_unknown_curve_raises():
+    import pytest
+    with pytest.raises(ValueError):
+        build_crossfade_merge_command(["/a.wav", "/b.wav"], 0.5, "/o/o.wav", curves="bogus")
+
+def test_merge_three_clips_zero_concat_chain():
+    cmd = build_crossfade_merge_command(["/a.wav", "/b.wav", "/c.wav"], 0.0, "/o/o.wav")
+    fc = cmd[cmd.index("-filter_complex") + 1]
+    assert fc.count("concat=n=2:v=0:a=1") == 2
+    assert "acrossfade" not in fc
+
 
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