MovieLite provides fine-grained control over audio tracks, allowing you to mix multiple audio sources, apply effects, and synchronize audio with video.
Accessing Video Audio Every VideoClip has an audio property that gives you access to its audio track:
from movielite import VideoClip, VideoWriter video = VideoClip( "input.mp4" , start = 0 , duration = 10 ) # Access the audio track print ( f "Audio duration: { video.audio.duration } s" ) print ( f "Audio start: { video.audio.start } s" ) print ( f "Audio volume: { video.audio.volume } " )
Modifying Video Audio Apply effects and adjustments to the video’s built-in audio track:
from movielite import VideoClip, VideoWriter, afx video = VideoClip( "sample.mp4" , start = 0 , duration = 10 ) # Modify the audio track video.audio.add_effect(afx.FadeIn( 2.0 )) video.audio.add_effect(afx.FadeOut( 2.0 )) video.audio.set_volume( 0.7 ) writer = VideoWriter( "output_with_faded_audio.mp4" , duration = 10 ) writer.add_clip(video) writer.write()
Changes to video.audio automatically apply to the video when rendered. The audio stays synchronized with the video.
Audio Effects Fade In Gradually increase volume from silence:
video.audio.add_effect(afx.FadeIn( duration = 2.0 ))
Fade Out Gradually decrease volume to silence:
video.audio.add_effect(afx.FadeOut( duration = 2.0 ))
Volume Control Set the overall volume level:
video.audio.set_volume( 0.5 ) # 50% volume video.audio.set_volume( 1.0 ) # 100% volume (default) video.audio.set_volume( 1.5 ) # 150% volume (amplify)
Fade In + Out
Reduce Volume
Combined
video.audio.add_effect(afx.FadeIn( 2.0 )).add_effect(afx.FadeOut( 2.0 ))
Adding Background Music Mix background music with your video’s audio:
from movielite import VideoClip, AudioClip, VideoWriter video = VideoClip( "sample.mp4" , start = 0 , duration = 10 ) # Reduce video audio volume video.audio.set_volume( 0.3 ) # Add background music music = AudioClip( "music.mp3" , start = 0 , duration = 10 ) music.set_volume( 0.7 ) writer = VideoWriter( "output_with_music.mp4" , duration = 10 ) writer.add_clip(video) writer.add_clip(music) writer.write()
Audio Mixing Behavior When multiple audio tracks overlap, MovieLite mixes them together:
Audio is added together (not replaced)
Adjust volumes to prevent clipping
Total volume of overlapping tracks shouldn’t exceed 1.0
If you have video audio at 0.7 and music at 0.7, the combined volume is 1.4, which may cause audio distortion. Balance your volumes accordingly.
Offsetting Audio from Video Delay or advance audio relative to video:
video = VideoClip( "sample.mp4" , start = 0 , duration = 10 ) # Video starts at 0, but audio starts at 2 seconds video.audio._start = 2.0 writer = VideoWriter( "output_audio_delayed.mp4" , duration = 12 ) writer.add_clip(video) writer.write()
Using _start directly breaks audio-video sync. Use this carefully and only when you specifically need independent audio timing.
Synchronized Timing Changes When you modify video timing, audio automatically stays synchronized:
video = VideoClip( "sample.mp4" , start = 0 , duration = 10 ) # Both video and audio start at 5 seconds video.set_start( 5.0 ) # Both video and audio are 8 seconds long video.set_duration( 8.0 ) writer = VideoWriter( "output_synced.mp4" , duration = 15 ) writer.add_clip(video) writer.write()
Multiple Audio Tracks Create complex audio mixes with multiple AudioClip instances:
from movielite import VideoClip, AudioClip, VideoWriter, afx video = VideoClip( "video.mp4" , start = 0 , duration = 30 ) video.audio.set_volume( 0.4 ) # Reduce original audio # Background music (full duration) music = AudioClip( "background.mp3" , start = 0 , duration = 30 , volume = 0.3 ) music.add_effect(afx.FadeIn( 2.0 )) music.add_effect(afx.FadeOut( 3.0 )) # Sound effect at 5 seconds sfx1 = AudioClip( "whoosh.wav" , start = 5.0 , volume = 0.8 ) # Another sound effect at 10 seconds sfx2 = AudioClip( "ding.wav" , start = 10.0 , volume = 0.6 ) # Voiceover from 15-25 seconds voiceover = AudioClip( "narration.mp3" , start = 15.0 , duration = 10 , volume = 0.9 ) voiceover.add_effect(afx.FadeIn( 0.5 )) voiceover.add_effect(afx.FadeOut( 0.5 )) writer = VideoWriter( "output_multi_audio.mp4" , duration = 30 ) writer.add_clip(video) writer.add_clips([music, sfx1, sfx2, voiceover]) writer.write()
Audio Timeline Visualization 0s 5s 10s 15s 20s 25s 30s Video [====================================] Music [fade in===================fade out---] SFX1 [whoosh] SFX2 [ding] Voice [fade in====fade out]
Ducking (Lowering Background Music) Duck background music when voiceover plays:
video = VideoClip( "video.mp4" , start = 0 , duration = 30 ) video.audio.set_volume( 0.2 ) # Full volume music for intro music_intro = AudioClip( "music.mp3" , start = 0 , duration = 10 , volume = 0.6 ) music_intro.add_effect(afx.FadeOut( 1.0 )) # Ducked music during voiceover music_ducked = AudioClip( "music.mp3" , start = 9 , duration = 12 , volume = 0.2 ) # Voiceover voiceover = AudioClip( "narration.mp3" , start = 10 , duration = 10 , volume = 0.9 ) # Full volume music for outro music_outro = AudioClip( "music.mp3" , start = 20 , duration = 10 , volume = 0.6 ) music_outro.add_effect(afx.FadeIn( 1.0 )) writer = VideoWriter( "output_ducked.mp4" , duration = 30 ) writer.add_clip(video) writer.add_clips([music_intro, music_ducked, voiceover, music_outro]) writer.write()
This technique keeps background music playing but reduces its volume during important narration or dialogue.
Looping Audio Loop a short audio clip to match video duration:
video = VideoClip( "video.mp4" , start = 0 , duration = 60 ) # Short music track that needs to loop music = AudioClip( "loop.mp3" , start = 0 , duration = 60 , volume = 0.4 ) music.loop( True ) # Enable looping music.add_effect(afx.FadeIn( 2.0 )) music.add_effect(afx.FadeOut( 2.0 )) writer = VideoWriter( "output_looped_audio.mp4" , duration = 60 ) writer.add_clip(video) writer.add_clip(music) writer.write()
Use a video’s audio track as a standalone audio source:
video1 = VideoClip( "video1.mp4" , start = 0 , duration = 10 ) video2 = VideoClip( "video2.mp4" , start = 0 , duration = 10 ) # Use video2's audio but video1's visuals video1.audio.set_volume( 0 ) # Mute video1's original audio writer = VideoWriter( "output_swapped_audio.mp4" , duration = 10 ) writer.add_clip(video1) writer.add_clip(video2.audio) # Add video2's audio track writer.write()
Removing Audio from Video Create a silent video:
video = VideoClip( "video.mp4" , start = 0 , duration = 10 ) video.audio.set_volume( 0 ) # Mute the audio writer = VideoWriter( "output_silent.mp4" , duration = 10 ) writer.add_clip(video) writer.write()
Or set the audio to None:
MovieLite supports common audio formats:
MP3 - Most common, compressedWAV - Uncompressed, high qualityAAC - Modern compressed formatFLAC - Lossless compressionOGG - Open source compressed format
Support depends on your FFmpeg installation. Most standard formats work out of the box.
Common Audio Mixing Patterns Background Music Throughout video = VideoClip( "video.mp4" ) video.audio.set_volume( 0.4 ) music = AudioClip( "music.mp3" , start = 0 , duration = video.duration, volume = 0.3 ) music.add_effect(afx.FadeIn( 2.0 )) music.add_effect(afx.FadeOut( 2.0 ))
Sound Effects at Specific Times sfx_times = [ 5.0 , 10.0 , 15.0 , 20.0 ] sfx_clips = [ AudioClip( "sfx.wav" , start = t, volume = 0.7 ) for t in sfx_times ] writer.add_clips(sfx_clips)
Crossfade Between Audio Tracks track1 = AudioClip( "song1.mp3" , start = 0 , duration = 30 , volume = 0.5 ) track1.add_effect(afx.FadeOut( 3.0 )) # Fade out last 3 seconds track2 = AudioClip( "song2.mp3" , start = 27 , duration = 30 , volume = 0.5 ) track2.add_effect(afx.FadeIn( 3.0 )) # Fade in first 3 seconds # 3 second overlap creates crossfade
Volume Guidelines Recommended volume levels:
Primary audio (dialogue, voiceover): 0.8 - 1.0Background music : 0.2 - 0.4Sound effects : 0.5 - 0.8Ambient sounds : 0.1 - 0.3 Adjust based on your content and prevent total volume from exceeding 1.0 to avoid clipping. Troubleshooting Audio and video out of sync
Ensure you’re not modifying audio._start unless needed
Use set_start() and set_duration() on the video clip, not the audio directly
Audio distortion or clipping
Total volume of overlapping tracks is too high
Reduce individual track volumes
Use volume levels that sum to ≤ 1.0
No audio in output
Check video.audio is not None
Verify volume is not set to 0
Ensure audio track duration overlaps with video
Background music too loud
Reduce music volume to 0.2 - 0.4
Increase video audio volume if needed
Use ducking technique during dialogue
Audio mixing happens during rendering
Multiple audio tracks have minimal performance impact
Audio effects are lightweight
Large audio files (>100MB) may use more memory
Next Steps
Effects Showcase Learn about audio and visual effects
Advanced Compositing Combine audio with complex video compositions
AudioClip API Complete AudioClip API reference
Audio Effects API Audio effects documentation
