Some video editing tasks require you to manipulate the dimensions of your videos. The ffmpeg tool provides a versatile platform for performing various video editing tasks, including resizing videos based on specific criteria. In this blog post, we'll explore how to use the 'if' statement within ffmpeg to conditionally resize videos.
Suppose you have a collection of videos with varying resolutions, and you want to resize all videos with a height greater than or equal to 480 pixels to a uniform height of 480 pixels, while maintaining the original aspect ratio. Here's how you can achieve this using the 'if' statement in ffmpeg:
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
Let's break down each component of this command:
- -i input.mp4: This specifies the input video file named "input.mp4."
- -c:v libx264: This specifies the video codec to use for encoding the output video. In this case, we're using the H.264 codec, which is widely supported and provides good compression.
- -crf 31: This sets the constant rate factor (CRF) for video encoding. A lower CRF value results in higher quality video but larger file size, while a higher CRF value produces lower quality video but smaller file size. 31 is a reasonable value for balancing quality and file size.
- -me_method umh: This sets the motion estimation method to "umh," which is known for providing good quality motion estimation.
- -bf 0: This sets the number of B-frames to 0, which disables B-frame encoding. This can improve encoding speed at the cost of slightly reduced video quality.
- -vf scale='if(gte(ih\,480)\,480\,iw)':-2: This is where the 'if' statement comes into play. It applies a conditional scaling filter to the video. The 'if' statement checks if the input video's height (ih) is greater than or equal to 480 pixels. If true, it scales the video to a height of 480 pixels while maintaining the original aspect ratio. If false, it leaves the video's dimensions unchanged.
- out.mp4: This specifies the output video file name, which will be created with the specified resizing parameters.
By utilizing the 'if' statement in ffmpeg, you can selectively resize videos based on specific criteria, such as height, width, or other video properties. This flexibility makes ffmpeg a powerful tool for automating video editing tasks and achieving consistent results.