FFmpeg command to scaling video proportionately to input

FFmpeg, a versatile multimedia processing tool, provides users with the capability to scale videos proportionately, ensuring that the aspect ratio is maintained during resizing. Whether you want to resize videos for different display sizes or optimize them for online platforms, this guide will walk you through the FFmpeg commands for scaling videos while preserving their original proportions.

  1. Installing FFmpeg:
    Ensure that FFmpeg is installed on your system before proceeding. Download the latest version from the official website (https://ffmpeg.org/download.html) or use package managers like Homebrew on macOS or APT on Linux.
  2. Navigate to the Video File Directory:
    Open a terminal or command prompt and navigate to the directory containing the video file you want to scale. Use the cd command to change the directory:
   cd /path/to/video/directory
  1. Execute FFmpeg Command – Scaling Proportionately:
    To scale a video proportionately, use the following FFmpeg command:
   ffmpeg -i input_video.mp4 -vf "scale=w:h" -c:a copy output_scaled_video.mp4

Breakdown of the command:

  • -i input_video.mp4: Specifies the input video file.
  • -vf "scale=w:h": Applies the scale filter to the video.
    • w:h: Specifies the desired width and height for the scaled video.
  • -c:a copy: Copies the audio stream without re-encoding.
  • output_scaled_video.mp4: Defines the output filename for the scaled video.
  1. Execute FFmpeg Command – Example with Scaling:
    For example, to scale a video to a width of 640 pixels while maintaining the original aspect ratio, the command would be:
   ffmpeg -i input_video.mp4 -vf "scale=640:-1" -c:a copy output_scaled_video_example.mp4

Breakdown of the command:

  • scale=640:-1: Specifies the width as 640 pixels and allows FFmpeg to automatically calculate the height to maintain the original aspect ratio.
  1. Adjusting Parameters:
  • Width (scale=w): Modify the width value to set the desired width for the scaled video.
  • Height (scale=:h): Modify the height value to set the desired height for the scaled video.
  • Automatic Aspect Ratio Calculation (scale=w:-1): Use -1 as the height to let FFmpeg automatically calculate the height to maintain the original aspect ratio.
  1. Execute the Commands:
    Press Enter to execute the FFmpeg commands. FFmpeg will process the video, scaling it according to the specified parameters. The progress will be displayed in the terminal.
  2. Viewing the Output:
    Once the process is complete, navigate to the output directory where the scaled videos are saved. Open the generated files using a media player to inspect the applied scaling.
  3. Execute FFmpeg Command – Scaling with Aspect Ratio Preservation:
    To scale a video while preserving a specific aspect ratio, use the following FFmpeg command:
   ffmpeg -i input_video.mp4 -vf "scale=w:h:force_original_aspect_ratio=decrease" -c:a copy output_scaled_aspect_ratio.mp4

Breakdown of the command:

  • force_original_aspect_ratio=decrease: Maintains the original aspect ratio and scales the video accordingly.
  • This ensures that the video is scaled while preserving its original aspect ratio.
  1. Customization and Additional Options:
    Explore FFmpeg’s extensive documentation for advanced options, such as using specific scaling filters, adjusting aspect ratios, or applying additional visual effects. Customizing the command allows you to create uniquely scaled videos based on your preferences.

In FFmpeg without knowing the size of the input frame, its resolution can be changed proportionately using the ih and iw parameters of the scale filter

for example to create a half sized video, we can use the next command

ffmpeg -i input.mpg -vf scale=iw/2:ih/2 output.mp4

Command for 90% sized video

ffmpeg -i input.mpg -vf scale=iw0.9:ih0.9 output.mp4

Scaling videos proportionately with FFmpeg offers a flexible and efficient solution for adapting content to different display sizes while maintaining the original aspect ratio. By following this comprehensive guide, you can use FFmpeg to scale videos, ensuring they fit seamlessly into various contexts without distortion.

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