When working with multimedia formats, the ffmpeg tool is a valuable resource for video processing tasks. Among its features, the versatile "if" statement allows for conditional filtering operations based on specific criteria.
We'll explore the "if" statement's usage within the context of ffmpeg to rescale videos based on their height.
Rescaling Videos with "if" Statement:
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
This command utilizes the "if" statement within the "-vf" filter option to rescale videos based on their height.
Understanding the Command:
- "ffmpeg": The command-line tool for multimedia processing.
- "-i input.mp4": Specifies the input video file.
- "-c:v libx264": Selects the H.264 video encoder.
- "-crf 31": Sets the CRF (Constant Rate Factor) value for video quality (lower values indicate higher quality).
- "-me_method umh": Specifies the motion estimation method (in this case, "umh").
- "-bf 0": Sets the number of B-frames to 0 (for faster encoding).
- "-vf scale='if(gte(ih\,480)\,480\,iw)':-2": Applies the "scale" filter with the "if" statement.
- "out.mp4": Specifies the output video file.
"if" Statement in "scale" Filter:
The "if" statement within the "scale" filter is used to conditionally resize the video based on its height:
- "if(gte(ih\,480)\,480\,iw)": This is the conditional expression.
- "gte(ih\,480)": Checks if the input video's height ("ih") is greater than or equal to 480 pixels.
- "480": If the condition is true (height ≥ 480), the video's height is set to 480 pixels.
- "iw": If the condition is false (height < 480), the video's width ("iw") is used for scaling (maintaining the aspect ratio).
- "-2": Specifies that the width should be automatically calculated based on the specified height to maintain the aspect ratio.
In summary, this command rescales videos with a height greater than or equal to 480 pixels to a height of 480 pixels, while maintaining their aspect ratio.