FFmpeg Pipe Raw Video to Another Tool macOS

This article provides a quick and practical guide on how to use FFmpeg on macOS to stream raw, uncompressed video directly to another command-line tool. You will learn how to configure FFmpeg to output to standard output (stdout), format the raw video stream correctly, and pipe that data into a receiving application in real-time.

To pipe raw video from FFmpeg to another tool on macOS, you must direct FFmpeg’s output to stdout using a single hyphen (-) and specify the raw video format. Because raw video contains no container or header metadata, you must also explicitly define the pixel format so the receiving tool knows how to decode the stream.

The Basic Command Structure

The standard command template for piping raw video is as follows:

ffmpeg -i input.mp4 -f rawvideo -pix_fmt yuv420p - | destination_tool

Command Breakdown

• -i input.mp4: Specifies your input source file (or stream).
• -f rawvideo: Forces FFmpeg to demux/mux the output as raw, uncompressed video frames.
• -pix_fmt yuv420p: Sets the pixel format. Popular options include yuv420p, rgb24, or uyvy422. The receiving tool must support the pixel format you choose.
• -: Represents stdout. This tells FFmpeg to write the video data directly to the terminal’s output stream instead of saving it to a file.
• |: The Unix pipe operator, which redirects the stdout of FFmpeg to the stdin of the next command.
• destination_tool: The command-line utility or script receiving the raw video stream.

Practical Example: Verification with FFplay

You can verify that your pipe is working correctly by piping the raw video directly into ffplay (the media player bundled with FFmpeg). Because raw video has no header, you must tell the receiving player the resolution, pixel format, and framerate of the incoming stream:

ffmpeg -i input.mp4 -f rawvideo -pix_fmt rgb24 - | ffplay -f rawvideo -pixel_format rgb24 -video_size 1920x1080 -framerate 30 -

Piping to Custom Scripts (Python/Node.js)

If you are piping raw video into a custom processing script (such as a Python script using OpenCV), your script must read from standard input (sys.stdin or sys.stdin.buffer).

For example, to pipe raw RGB frames to a Python script:

ffmpeg -i input.mp4 -f rawvideo -pix_fmt rgb24 - | python3 process_stream.py

Inside your Python script, you would read the exact number of bytes required for each frame based on the resolution and pixel format (e.g., width * height * 3 bytes per frame for 24-bit RGB).