HDMI RX

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The HDMI RX (Receiver) port on Axon allows you to capture video input from HDMI sources. This documentation covers how to set up and receive video data using two Axon boards and the V4L2 (Video4Linux2) tool.

Note

Instead of using another Axon board as a video source, you can use any other source. This page shows how to connect two Axon boards.

Getting Started

Prerequisites

  • 2x Axon boards (one as TX/transmitter and one as RX/receiver)

  • 2x HDMI cables

  • Mini-HDMI to HDMI converter

Hardware Setup

Connect the Boards

  1. Connect the HDMI TX output from the first Axon board (TX board) to Mini-HDMI to HDMI converter then connect HDMI RX input of the second Axon board (RX board) to it.

  2. Power on both boards

  3. Ensure both boards are running and have network connectivity

Receiving the data

Verify HDMI RX Detection

  1. SSH into the RX Axon board:

ssh root@<RX-BOARD-IP>

  1. Install v4l2 tools

sudo apt install v4l-utils

  1. Check if the HDMI RX port is detected:

v4l2-ctl --list-devices

  1. You should see output listing the HDMI RX device (typically /dev/video0 or similar):

rk_hdmirx (fde0000.hdmirx-controller):
   /dev/video0

  1. You can get more info about connected device by :

v4l2-ctl -d /dev/video0 --all

Receiving Video Data with V4L2

Note

You can either use qv4l2 (the official V4L2 GUI tool) to detect devices and view the video or use the terminal. Both methods are explained below.

Using qv4l2(GUI Tool)

Step 1: Install the GUI tool (qv4l2) on RX Axon

sudo apt install qv4l2

Step 2: Open qv4l2

qv4l2

Step 3: Click the ‘Start Capturing’ button as shown below

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Using Terminal

Step 1: Verify Supported Formats

Check the available video formats and resolutions supported by the HDMI RX:

v4l2-ctl --device=/dev/video0 --list-formats-ext

Example output:

ioctl: VIDIOC_ENUM_FMT

Type: Video Capture Multiplanar

[0]: 'BGR3' (24-bit BGR 8-8-8)
[1]: 'NV24' (Y/CbCr 4:4:4)
[2]: 'NV16' (Y/CbCr 4:2:2)
[3]: 'NV12' (Y/CbCr 4:2:0)

Step 2: Detect Input Signal

Check if a video signal is being received:

v4l2-ctl --device=/dev/video0 --get-fmt-video

You should see information about the detected input resolution and format:

Format Video Capture:
  Width/Height      : 1920/1080
  Pixel Format      : 'UYVY'
  Field             : None
  Bytes per Line    : 3840
  Size Image        : 8294400
  Colorspace        : Default
  Transfer Function : Default
  YCbCr/HSV Encoding: Default
  Quantization      : Default

Step 3: Capture Video Stream

Use V4L2 to capture and save the video stream:

v4l2-ctl --device=/dev/video0 --stream-mmap --stream-count=100 --stream-to=capture.yuv

This command:

  • --device=/dev/video0: Specifies the HDMI RX device

  • --stream-mmap: Uses memory-mapped I/O for efficient streaming

  • --stream-count=100: Captures 100 frames

  • --stream-to=capture.yuv: Saves the captured video to a file

Step 4: View Captured Video

Convert and view the captured YUV data using ffmpeg (if installed):

ffplay -f rawvideo -pixel_format uyvy422 -video_size 1920x1080 -framerate 60 capture.yuv

Or save as a video file:

ffmpeg -f rawvideo -pixel_format uyvy422 -video_size 1920x1080 -framerate 60 -i capture.yuv output.mp4

Common V4L2 Commands

Command

Description

v4l2-ctl --list-devices

List all V4L2 devices

v4l2-ctl -d /dev/video0 --list-formats-ext

List supported video formats and resolutions

v4l2-ctl -d /dev/video0 --get-fmt-video

Get current video format and resolution

v4l2-ctl -d /dev/video0 --set-fmt-video=width=1920,height=1080

Set specific video resolution

v4l2-ctl -d /dev/video0 --stream-mmap --stream-count=N

Capture N frames from the HDMI RX input

Troubleshooting

No HDMI RX device detected

  • Verify the HDMI cable is properly connected to both boards

  • Ensure the TX board is actively transmitting a video signal

  • Check if the HDMI RX driver is loaded: lsmod | grep hdmirx

  • Reboot the RX board if the device is not detected

No signal detected in v4l2-ctl

  • Confirm the TX board is sending video data

  • Check HDMI cable connectivity

  • Try resetting both boards and reconnecting

  • Verify the HDMI source resolution is supported by Axon

Cannot capture video or corrupted data

  • Ensure both boards have adequate power supply

  • Try capturing fewer frames first (--stream-count=10)

  • Check if the pixel format is correct

  • Verify network connectivity if using remote access

Note

The HDMI RX input resolution is detected automatically from the incoming signal. The supported resolutions depend on the HDMI TX source and board capabilities up to 4K resolution.