Combine videos using ffmpeg

I wanted to combine videos using the tool. I had two videos in 9x16 format and wanted to combine side by side.

With a little bit of trial and error, I was able to achieve this using ffmpeg

The exact command is

ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex "[0:v]scale=540:960:force_original_aspect_ratio=decrease,pad=540:960:(ow-iw)/2:(oh-ih)/2[v0];[1:v]scale=540:960:force_original_aspect_ratio=decrease,pad=540:960:(ow-iw)/2:(oh-ih)/2[v1];[v0][v1]hstack=inputs=2[v]" -map "[v]" -map 0:a -c:v libx264 -c:a aac output.mp4

Breaking Down the Command

Let’s understand what each part of this complex command does:

Input Files

-i video1.mp4 -i video2.mp4

This specifies our two input videos. FFmpeg will reference them as [0] and [1] respectively.

Filter Chain Explanation

The -filter_complex parameter contains several operations:

1. Scale and Pad First Video:

[0:v]scale=540:960:force_original_aspect_ratio=decrease,pad=540:960:(ow-iw)/2:(oh-ih)/2[v0]
  • scale=540:960: Resize to 540x960 pixels
  • force_original_aspect_ratio=decrease: Maintain aspect ratio, making the video smaller if needed
  • pad=540:960:(ow-iw)/2:(oh-ih)/2: Add padding to center the video in a 540x960 frame
  • [v0]: Label this processed video as “v0”

2. Scale and Pad Second Video:

[1:v]scale=540:960:force_original_aspect_ratio=decrease,pad=540:960:(ow-iw)/2:(oh-ih)/2[v1]

Same process for the second video, labeled as “v1”.

3. Horizontal Stack:

[v0][v1]hstack=inputs=2[v]
  • hstack: Horizontally stack the two processed videos
  • inputs=2: Specify we’re combining 2 video streams
  • [v]: Label the final combined video

Output Mapping and Encoding

-map "[v]" -map 0:a -c:v libx264 -c:a aac output.mp4
  • -map "[v]": Use our combined video stream
  • -map 0:a: Use audio from the first video
  • -c:v libx264: Encode video using H.264 codec
  • -c:a aac: Encode audio using AAC codec

Its great that in Linux even without tools such as Adobe Premiere Pro, you can achieve so much.