feat: audio_edit_filters helper + optional -af chain on build_audio_clip_command

tests/test_utils.py

@@ -76,6 +76,31 @@ def test_audio_clip_command_extension_case_insensitive():
     assert "flac" in build_audio_clip_command("/in.mp4", 0, 1, "/o/A.FLAC")
 
 
+def test_audio_edit_filters_empty_when_defaults():
+    from core.ffmpeg import audio_edit_filters
+    assert audio_edit_filters(duration=3.0) == []
+
+def test_audio_edit_filters_fade_normalize_gain():
+    from core.ffmpeg import audio_edit_filters
+    f = audio_edit_filters(duration=10.0, fade_in=0.5, fade_out=2.0,
+                           normalize=True, gain_db=-3.0)
+    assert "afade=t=in:st=0:d=0.5" in f
+    assert "afade=t=out:st=8.0:d=2.0" in f      # fade-out starts at duration - fade_out
+    assert "loudnorm" in f
+    assert "volume=-3.0dB" in f
+
+def test_audio_clip_command_no_filters_unchanged():
+    cmd = build_audio_clip_command("/in.mp4", 1.0, 2.0, "/o/a.wav")
+    assert "-af" not in cmd
+
+def test_audio_clip_command_appends_filter_chain():
+    cmd = build_audio_clip_command("/in.mp4", 1.0, 2.0, "/o/a.wav",
+                                   filters=["afade=t=in:st=0:d=0.5", "loudnorm"])
+    i = cmd.index("-af")
+    assert cmd[i + 1] == "afade=t=in:st=0:d=0.5,loudnorm"
+    assert i < len(cmd) - 1 and cmd[-1] == "/o/a.wav"
+
+
 # --- ProcessedDB ---
 
 def test_db_add_and_get_markers():