Force stereo videos to solve issue with 5.1 sound videos

Author: benoit74

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 - Upgrade to wombat 3.8.8 and other Python/JS dependencies (#249)
+- Force stereo videos to solve issue with 5.1 sound videos (#250)
 
 ## [5.1.0] - 2025-01-21
 

src/zimscraperlib/video/presets.py

@@ -22,6 +22,7 @@ class VoiceMp3Low(Config):
         "-codec:a": "mp3",  # audio codec
         "-ar": "44100",  # audio sampling rate
         "-b:a": "48k",  # target audio bitrate
+        "-ac": "2",  # force stereo even if input is higher
     }
 
 
@@ -49,6 +50,7 @@ class VideoWebmLow(Config):
         "-codec:a": "libvorbis",  # audio codec
         "-b:a": "48k",  # target audio bitrate
         "-ar": "44100",  # audio sampling rate
+        "-ac": "2",  # force stereo even if input is higher
     }
 
 
@@ -77,6 +79,7 @@ class VideoMp4Low(Config):
         "-ar": "44100",  # audio sampling rate
         "-b:a": "48k",  # target audio bitrate
         "-movflags": "+faststart",  # extra flag
+        "-ac": "2",  # force stereo even if input is higher
     }
 
 
@@ -101,6 +104,7 @@ class VideoWebmHigh(Config):
         "-codec:a": "libvorbis",  # audio codec
         "-b:a": "48k",  # target audio bitrate
         "-ar": "44100",  # audio sampling rate
+        "-ac": "2",  # force stereo even if input is higher
     }
 
 

tests/video/test_video.py

@@ -180,7 +180,7 @@ def test_preset_video_webm_low():
     config = VideoWebmLow()
     assert config.VERSION == 3
     args = config.to_ffmpeg_args()
-    assert len(args) == 24
+    assert len(args) == 26
     options_map = [
         ("codec:v", "libvpx-vp9"),
         ("codec:a", "libvorbis"),
@@ -193,6 +193,7 @@ def test_preset_video_webm_low():
         ("vf", "scale='480:trunc(ow/a/2)*2'"),
         ("g", "240"),
         ("speed", "4"),
+        ("ac", "2"),
     ]
     for option, val in options_map:
         idx = args.index(f"-{option}")
@@ -213,7 +214,7 @@ def test_preset_video_webm_high():
     config = VideoWebmHigh()
     assert config.VERSION == 2
     args = config.to_ffmpeg_args()
-    assert len(args) == 22
+    assert len(args) == 24
     options_map = [
         ("codec:v", "libvpx-vp9"),
         ("codec:a", "libvorbis"),
@@ -225,6 +226,7 @@ def test_preset_video_webm_high():
         ("qmax", "54"),
         ("g", "240"),
         ("speed", "1"),
+        ("ac", "2"),
     ]
     for option, val in options_map:
         idx = args.index(f"-{option}")
@@ -245,7 +247,7 @@ def test_preset_video_mp4_low():
     config = VideoMp4Low()
     assert config.VERSION == 1
     args = config.to_ffmpeg_args()
-    assert len(args) == 24
+    assert len(args) == 26
     options_map = [
         ("codec:v", "h264"),
         ("codec:a", "aac"),
@@ -258,6 +260,7 @@ def test_preset_video_mp4_low():
         ("qmin", "30"),
         ("qmax", "42"),
         ("vf", "scale='480:trunc(ow/a/2)*2'"),
+        ("ac", "2"),
     ]
     for option, val in options_map:
         idx = args.index(f"-{option}")
@@ -303,11 +306,12 @@ def test_preset_voice_mp3_low():
     config = VoiceMp3Low()
     assert config.VERSION == 1
     args = config.to_ffmpeg_args()
-    assert len(args) == 9
+    assert len(args) == 11
     options_map = [
         ("codec:a", "mp3"),
         ("ar", "44100"),
         ("b:a", "48k"),
+        ("ac", "2"),
     ]
     for option, val in options_map:
         idx = args.index(f"-{option}")