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Merging Video and Audio Files with FFmpeg

ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 output.mp4

Parameter Explanation

Parameter Description
-i video.mp4 First input: the video file
-i audio.wav Second input: the audio file
-c:v copy Copy the video stream without re-encoding
-c:a aac Convert audio to AAC format
-map 0:v:0 Map the first video stream from the first input
-map 1:a:0 Map the first audio stream from the second input

Practical Examples

Example 1: Replace audio while keeping original volume

ffmpeg -i video.mp4 -i audio.mp3 -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 -shortest output.mp4

Replaces the original audio with a new soundtrack and stops when the shortest stream ends.

Example 2: Merge video with multiple audio tracks

ffmpeg -i video.mp4 -i english.wav -i spanish.wav -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 -map 2:a:0 -metadata:s:a:0 language=eng -metadata:s:a:1 language=spa multi_language.mp4

Creates a video with two audio tracks (English and Spanish) with proper language metadata.

Example 3: Merge and delay audio

ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 -af "adelay=2000|2000" -shortest output.mp4

Merges audio with video but delays the audio by 2 seconds (useful for sync issues).