Change Video Frame Rate

How to change the frame rate of a video from 24 fps to 30 fps.

The code snippets in this article are from the simple_video_framerate Python sample.

Source Video

For a source video we use the MP4 file from the TED talk video What’s the next window into our universe? by Andrew Connolly. The original video format is Wide 480p or 16:9, 854 x 480.

Code

This code takes an MP4 file encoded at 24 fps, and increases the video frame rate to 30 fps. The audio stream is copied from the source as is.

Initialize AVBlocks and Configure Transcoder

The sample uses hardcoded input and output file paths. The main function initializes the library and calls change_framerate. It creates a MediaInfo object to probe the input file, then creates input and output sockets. The output socket is cloned from the input socket, then the frame rate is set to 30 fps.

def main():
    # Hardcoded input and output file paths (no command line parsing)
    # Paths are relative to the working directory from which the sample is run
    input_path = "AndrewConnolly_2014.mp4"
    output_path = "AndrewConnolly_2014_30fps.mp4"

    Library.initialize()

    # Set license information. To run AVBlocks in demo mode, comment the next line out
    # Library.set_license("<license-string>")

    result = change_framerate(input_path, output_path)

    Library.shutdown()

    return 0 if result else 2


def change_framerate(input_path: str, output_path: str) -> bool:
    # Ensure output directory exists
    output_dir = os.path.dirname(output_path)
    if output_dir and not os.path.exists(output_dir):
        os.makedirs(output_dir)

    # Delete output file if it exists (transcoder will fail otherwise)
    if os.path.exists(output_path):
        os.remove(output_path)

    # Create MediaInfo to probe the input file
    with MediaInfo() as media_info:
        media_info.inputs[0].file = input_path

        if not media_info.open():
            print_error("Open MediaInfo", media_info.error)
            return False

        # Create input socket from probed media info
        input_socket = MediaSocket.from_media_info(media_info)

        # Clone the input socket to start with identical output configuration
        output_socket = input_socket.clone()
        output_socket.file = output_path

        # Get the output video pin and set frame rate to 30 fps
        if len(output_socket.pins) < 1:
            print("No video pin found in input")
            return False

        out_video_pin = output_socket.pins[0]
        out_video_stream = out_video_pin.stream_info
        if not isinstance(out_video_stream, VideoStreamInfo):
            print("Output pin is not a video stream")
            return False

        # Change the frame rate from 24 fps to 30 fps
        out_video_stream.frame_rate = 30.0

        # Create Transcoder and configure it
        with Transcoder() as transcoder:
            transcoder.allow_demo_mode = True
            transcoder.inputs.add(input_socket)
            transcoder.outputs.add(output_socket)

            if not transcoder.open():
                print_error("Transcoder open", transcoder.error)
                return False

            if not transcoder.run():
                print_error("Transcoder run", transcoder.error)
                transcoder.close()
                return False

            transcoder.close()

    return True

Complete Code

Here’s the complete working example that demonstrates frame rate conversion using AVBlocks for Python.

"""
Change the frame rate of a video from 24 fps to 30 fps.

This sample demonstrates the basic AVBlocks frame rate conversion workflow with
hardcoded input and output file paths (no command line parsing).
"""

import os
import sys

from avblocks import (
    Library, MediaInfo, MediaSocket, Transcoder,
    VideoStreamInfo, ErrorFacility
)


def print_error(action: str, error) -> None:
    """Print error information."""
    if action:
        print(f"{action}: ", end="")

    if error.facility == ErrorFacility.Success:
        print("Success")
        return

    print(f"{error.message or ''}, facility:{error.facility} code:{error.code} hint:{error.hint or ''}")


def change_framerate(input_path: str, output_path: str) -> bool:
    # Ensure output directory exists
    output_dir = os.path.dirname(output_path)
    if output_dir and not os.path.exists(output_dir):
        os.makedirs(output_dir)

    # Delete output file if it exists (transcoder will fail otherwise)
    if os.path.exists(output_path):
        os.remove(output_path)

    # Create MediaInfo to probe the input file
    with MediaInfo() as media_info:
        media_info.inputs[0].file = input_path

        if not media_info.open():
            print_error("Open MediaInfo", media_info.error)
            return False

        # Create input socket from probed media info
        input_socket = MediaSocket.from_media_info(media_info)

        # Clone the input socket to start with identical output configuration
        output_socket = input_socket.clone()
        output_socket.file = output_path

        # Get the output video pin and set frame rate to 30 fps
        if len(output_socket.pins) < 1:
            print("No video pin found in input")
            return False

        out_video_pin = output_socket.pins[0]
        out_video_stream = out_video_pin.stream_info
        if not isinstance(out_video_stream, VideoStreamInfo):
            print("Output pin is not a video stream")
            return False

        # Change the frame rate from 24 fps to 30 fps
        out_video_stream.frame_rate = 30.0

        # Create Transcoder and configure it
        with Transcoder() as transcoder:
            transcoder.allow_demo_mode = True
            transcoder.inputs.add(input_socket)
            transcoder.outputs.add(output_socket)

            if not transcoder.open():
                print_error("Transcoder open", transcoder.error)
                return False

            if not transcoder.run():
                print_error("Transcoder run", transcoder.error)
                transcoder.close()
                return False

            transcoder.close()

    return True


def main():
    # Hardcoded input and output file paths (no command line parsing)
    # Paths are relative to the working directory from which the sample is run
    input_path = "AndrewConnolly_2014.mp4"
    output_path = "AndrewConnolly_2014_30fps.mp4"

    Library.initialize()

    # Set license information. To run AVBlocks in demo mode, comment the next line out
    # Library.set_license("<license-string>")

    result = change_framerate(input_path, output_path)

    Library.shutdown()

    return 0 if result else 2


if __name__ == '__main__':
    sys.exit(main())

How to Run

See the simple_video_framerate Python sample for details.

Command Line

This sample uses hardcoded input and output file paths — no command line parsing.

simple-video-framerate

Examples

Install the package in development mode from the repository root (this installs the sample command):

source .venv/bin/activate
uv pip install --editable .

Download the sample video, the MP4 file from the TED talk video What’s the next window into our universe? by Andrew Connolly (Wide 480p, 854x480, 24 fps):

cd samples/simple_video_framerate
curl -L -o AndrewConnolly_2014.mp4 "https://archive.org/download/AndrewConnolly_2014/AndrewConnolly_2014.mp4"

Run the sample (the input/output file paths are relative to the working directory):

simple-video-framerate

The converted output file AndrewConnolly_2014_30fps.mp4 will be created in the samples/simple_video_framerate directory.