Using if statement in ffmpeg

Discover Resizing Magic with ffmpeg and the Conditional Scaling Filter

Ever encountered a video collection with inconsistent resolutions, causing playback issues across devices? Unleash the power of ffmpeg and the versatile if statement to automate your resizing tasks and ensure seamless viewing experiences.

ffmpeg as a command-line video manipulation tool offers a wide range of capabilities, including resizing videos to specific dimensions or aspect ratios. The if statement takes conditional expressions to the next level, allowing you to apply resizing operations based on specific conditions.

Stepping into the Conditional Scaling Realm

To illustrate the conditional scaling capability, consider the following command:

ffmpeg -i input.mp4 -c:v libx264 -crf 31 -me_method umh -bf 0 -vf scale='if(gte(ih\,480)\,480\,iw)':-2 out.mp4

Breaking down this command:

• -i input.mp4: Specifies the input video file.
• -c:v libx264: Selects the H.264 video codec for encoding.
• -crf 31: Sets the CRF (Constant Rate Factor) to 31, balancing video quality and file size.
• -me_method umh: Utilizes the Ultra Fast Motion Estimation algorithm for faster encoding.
• -bf 0: Disables B-frames, further reducing encoding time.
• -vf scale='if(gte(ih\,480)\,480\,iw)':-2: Here's where the conditional scaling magic happens.

Dissecting the Conditional Scaling Filter

The scale filter in ffmpeg is responsible for resizing videos. Let's break down its syntax within the if statement:

• if(gte(ih\,480)\,480\,iw): This expression evaluates whether the input video's height (ih) is greater than or equal to 480 pixels.
• 480: If the condition is true, the height is set to 480 pixels.
• iw: If the condition is false, the width is used as the scaling factor, preserving the aspect ratio.
• -2: This option instructs ffmpeg to automatically calculate the width that maintains the video's aspect ratio.

Applying the Conditional Scaling Magic

With this command, ffmpeg will analyze each input video. If the height is 480 pixels or more, it will resize the video to a height of 480 pixels, maintaining the aspect ratio by proportionally adjusting the width. Videos with heights less than 480 pixels will remain untouched.

Additional Conditional Scaling Scenarios

The conditional scaling filter offers even more flexibility:

• Upscaling Prevention: To prevent upscaling, which can introduce quality issues, you can use the min() function. For example, to limit the height to 720p while maintaining the aspect ratio, use:

-vf scale='min(1280,iw)':'min(720,ih)'

• Constrained Resizing: To specify both height and width while preserving the aspect ratio, use:

-vf scale='min(1280,iw)':'min(720,ih)':force_original_aspect_ratio=decrease

Conclusion

Harnessing the power of ffmpeg's if statement and the scale filter, you can automate conditional resizing tasks, ensuring consistent video resolutions across your collection. Whether you need to downscale large videos, upscale smaller ones, or maintain aspect ratios, these techniques provide ultimate control and flexibility.