How to Output Video to DeckLink Using FFmpeg

This article provides a step-by-step guide on how to output video directly to a Blackmagic Design DeckLink playback card using FFmpeg. You will learn how to list your available DeckLink devices, identify supported video formats, and construct the precise FFmpeg command required for real-time, broadcast-quality playout.

Prerequisites

To output to a DeckLink card, your version of FFmpeg must be compiled with DeckLink support. This requires the Blackmagic DeckLink SDK and the --enable-decklink configuration flag during compilation. You also need the Blackmagic Desktop Video drivers installed on your system.

Step 1: List Available DeckLink Devices

Before sending video to a card, you must find the exact name of your DeckLink playback device. Run the following command to list all connected Blackmagic input and output devices:

ffmpeg -f decklink -list_devices 1 -i dummy

Identify your playback device from the output list (for example, "DeckLink Mini Monitor" or "DeckLink Duo (1)").

Step 2: List Supported Video Formats

DeckLink cards are strict about the video formats, resolutions, and frame rates they accept. To see the formats supported by your specific card, run:

ffmpeg -f decklink -list_formats 1 -i "Your Device Name"

Replace "Your Device Name" with the exact name found in Step 1. The output will show a list of format codes (such as hp50 for 1080p50 or Hi59 for 1080i59.94).

Step 3: Run the Playback Command

Once you have the device name and the desired format code, you can stream a video file directly to the card.

Use the following template command:

ffmpeg -re -i input.mp4 -f decklink -pix_fmt uyvy422 -format_code hp50 "DeckLink Mini Monitor"

Explanation of Key Parameters:

• -re: Tells FFmpeg to read the input file in real-time. Without this, FFmpeg will process the file as fast as possible, causing playback issues.
• -i input.mp4: The path to your input video file.
• -f decklink: Forces the output format to use the DeckLink driver.
• -pix_fmt uyvy422: Sets the pixel format. DeckLink cards typically require uyvy422 (8-bit) or yuv422p10le (10-bit).
• -format_code hp50: Tells the DeckLink card to output in a specific resolution and frame rate (in this case, 1080p at 50 fps). Refer to the list generated in Step 2 for your card’s supported codes.
• "DeckLink Mini Monitor": The exact name of your playback card.

Outputting Audio

By default, FFmpeg will attempt to route the audio channels of your source file to the DeckLink card’s SDI/HDMI embedded audio outputs. If you need to map specific audio channels or adjust layout, you can use FFmpeg’s standard audio mapping flags (-map) before the output destination.