Set Frame Rate in FFmpeg for Image Sequence

Converting a sequence of still images into a video is a common task in FFmpeg, but setting the correct frame rate requires placing the appropriate flags in the right order. This article explains how to define the input and output frame rates using the -framerate and -r options, the differences between them, and how to avoid common pitfalls like dropped or duplicated frames.

The Standard Method: Use the -framerate Option

To define how many images FFmpeg reads per second, use the -framerate option before the input flag (-i). This ensures that each image in your sequence corresponds to exactly one video frame at your desired playback speed.

ffmpeg -framerate 30 -i input_%04d.png -c:v libx264 -pix_fmt yuv420p output.mp4

In this command:

• -framerate 30 instructs FFmpeg to read 30 images per second.
• -i input_%04d.png specifies the sequential image pattern (e.g., input_0001.png, input_0002.png).
• -c:v libx264 encodes the video using the H.264 codec.
• -pix_fmt yuv420p ensures broad compatibility across standard media players.

Setting Separate Input and Output Frame Rates

If you want your source images to display at a specific rate, but you need the final video container to conform to a standard broadcast or display rate, combine -framerate (input) with -r (output).

Place -framerate before the input and -r after the input:

ffmpeg -framerate 24 -i input_%04d.png -r 60 -c:v libx264 -pix_fmt yuv420p output.mp4

• Input (-framerate 24): FFmpeg reads 24 distinct images per second of playback.
• Output (-r 60): FFmpeg resamples the stream to 60 frames per second by duplicating frames, maintaining the intended playback speed while meeting the 60 fps container requirement.

Why You Should Avoid Using -r as an Input Flag

While -r can technically be placed before -i, it behaves differently than -framerate when dealing with image demuxers. Using -r before -i can cause FFmpeg to drop or duplicate frames during the initial read phase, leading to stutter or skipped images. Always use -framerate for the input image sequence and reserve -r for defining the output container rate.

Using Glob Patterns (Linux and macOS)

If your image filenames are not strictly sequential numbers, you can use pattern matching with the -pattern_type glob option, while still applying -framerate:

ffmpeg -framerate 25 -pattern_type glob -i '*.png' -c:v libx264 -pix_fmt yuv420p output.mp4

This reads all matching .png files in alphabetical order at 25 frames per second.