Lately I have been working on a hobby programming project that automatically converts text or web pages into videos. Many functionalities of the software come from an open source project called FFmpeg. It is great for working with video and images. Below you will find the commands and annotations I made over the past few weeks about using FFmpeg, which is not always trivial.

Overlay image on video

ffmpeg -i input.mp4 -i 1.png -filter_complex "[0:v][1:v] overlay=25:25:enable='between(t,0,20)'" \
-pix_fmt yuv420p -c:a copy output.mp4

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Add audio to video (if video has audio, needs to map video from input 0 and audio from input 1)

ffmpeg -i matrix-16.mp4 -i port-audio.mp3 -map 0:v -map 1:a -acodec aac -strict -2 output.mp4

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Add audio to video: stream copy

ffmpeg -i video.avi -i audio.mp3 -codec copy -shortest output.avi

Omitting the -map option will use the default stream selection. This will work if your video input has no audio.

This example uses -codec copy to stream copy (no re-encoding; quality is preserved and it is fast).
The -shortest option will make output.avi the same duration as the shortest input.

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Add audio to video: re-encode

If your output doesn’t like the original formats, or if you want to change formats you can specify the encoders:

ffmpeg -i video.avi -i audio.mp3 -c:v libx264 -c:a libvorbis -shortest output.mkv

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To manually choose specific streams

Sometimes the default stream selection won’t give you the result you want. In this example video.mp4 has video and audio, and audio.m4a only has audio. Use -map to choose video from video.mp4 and audio from audio.m4a:

ffmpeg -i video.mp4 -i audio.m4a -map 0:v -map 1:a -c copy -shortest output.mp4

-map 0:v – From input 0 (the first input, which is video.mp4) choose the video stream(s).
-map 1:a – From input 1 (the second input, which is audio.m4a) choose the audio stream(s).

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Mixing/combining two audio inputs into one (needs tweaking, see below for a better version)

Take video from video.webm, and use the amerge filter to combine the audio from video.webm and audio.oga:

ffmpeg -i video.webm -i audio.oga -filter_complex "[0:a][1:a]amerge=inputs=2[a]" -map 0:v -map "[a]" -c:v copy -c:a libvorbis -ac 2 -shortest out.webm

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Generate silent audio

You can use the anullsrc filter to make a silent audio stream. The filter allows you to choose the desired channel layout (mono, stereo, 5.1, etc) and the sample rate.

ffmpeg -i video.mp4 -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=44100 -c:v copy -shortest output.mp4

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Concat mp3

ffmpeg -i "concat:intro-1.mp3|audio.mp3" -acodec copy output.mp3

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Overlay many images at the same time

ffmpeg -i output.mp4 -i 1.png -i 2.png -i 3.png -i 4.png -i 5.png -i 6.png -i 7.png -i 8.png -filter_complex "[0][1] overlay=0:0:enable='between(t,4,9)'[v1];[v1][2] overlay=0:0:enable='between(t,9,15)'[v2];[v2][3] overlay=0:0:enable='between(t,15,20)'[v3];[v3][4] overlay=0:0:enable='between(t,20,25)'[v4];[v4][5] overlay=0:0:enable='between(t,25,31)'[v5];[v5][6] overlay=0:0:enable='between(t,31,33)'[v6];[v6][7] overlay=0:0:enable='between(t,33,39)'[v7]; [v7][8] overlay=0:0:enable='between(t,39,47)'[v8];[v8][1] overlay=0:0:enable='gt(t,47)'[v9]" -map "[v9]" -map 0:a -pix_fmt yuv420p -c:a copy 1.mp4

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Cut video length at the end

ffmpeg -i input.mp4 -c copy -t 00:00:10.0 background.mp4

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Cut beginning and end of video

You can use the -ss option to specify a start timestamp, and the -t option to specify the encoding duration. The timestamps need to be in HH:MM:SS.xxx format or in seconds.

The following would clip the first 30 seconds, and then clip everything that is 10 seconds after that:

ffmpeg -i input.wmv -ss 00:00:30.0 -c copy -t 00:00:10.0 output.wmv
ffmpeg -i input.wmv -ss 30 -c copy -t 10 output.wmv

Note that -t is an output option and always needs to be specified after -i.

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overlay 2 audio files, adjusting respective volumes

ffmpeg -i audio.mp3 -i 2.mp3 -filter_complex "[0:a]aformat=sample_fmts=fltp:sample_rates=44100:channel_layouts=stereo,volume=2.5[a1]; [1:a]aformat=sample_fmts=fltp:sample_rates=44100:channel_layouts=stereo,volume=0.3[a2]; [a1][a2]amerge,pan=stereo:c0<c0+c2:c1<c1+c3[out]" -map "[out]" -c:a libmp3lame -q:a 0 -shortest output.mp3

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Concat 2 videos with list.txt

ffmpeg -f concat -i list.txt -c copy background.mp4

list.txt should be:
file 1.mp4
file 2.mp4

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Adjust framerate and resolution of video

ffmpeg -i 3.mp4 -r 25 -s 1920x1080 output.mp4