captureHdmiAudio
Currently (L4T R24.2.1@dd13899) it is possible to capture audio, but only with these limitations:
- Only on HDMI-In-B
- Max. 2 channels (stereo)
- You need to connect some headers with wires
The HDMI-In A is fixed connected to I2S4 through the camera connector on the Jetson TX1 board. We have not yet found a way to use I2S4. But for HDMI-In B the I2S connections are connected to a 0.1" header (X501) on the HDMI2CSI board. These pins can be connected to I2S1 which is available on J21 header of the Jetson.
To capture stereo audio on HDMI-In-B follow these steps:
Use wires to connect the 4 pins of the I2S interface (GND, CLK, OUT, LRC) from the X501 connector on the HDMI2CSI board to the J21 header of the Jetson board. Make sure to twist the wires to reduce EMI. (Optimal is to twist each signal with a ground wire)
First we need to export some GPIOs to make them available for user space:
echo 8 > /sys/class/gpio/export #LRC
echo 9 > /sys/class/gpio/export #Data in
echo 11 > /sys/class/gpio/export #SCLK
echo 8 > /sys/class/gpio/unexport
echo 9 > /sys/class/gpio/unexport
echo 11 > /sys/class/gpio/unexport
Load the driver for the tc358840 bridge IC:
sudo modprobe tc358840
Start a video capturing pipeline on /dev/video2 (e.g.):
gst-launch-1.0 v4l2src device=/dev/video2 ! 'video/x-raw, width=1920, height=1080, framerate=60/1, format=UYVY' ! nvvidconv ! 'video/x-raw(memory:NVMM), format=I420' ! nvoverlaysink
Record audio on the ALSA device 1,0 (e.g. use arecord):
arecord -f S16_LE -c 2 -r 48000 -d 5 -D hw:1,0 test.wav
Note that in the EDID currently the following Audio settings are allowed:
- Format = Linear PCM
- Format = Uncompressed, 16 Bit
- Number of Channels = 2
- Supported Sampling Frequencies
- 32 kHz
- 44 kHz
- 48 kHz
Therefore your HDMI source has a choice of which sampling frequency it may deliver. Currently there is not yet a mechanism in the drivers to determine which sampling frequency was chosen by the source.