How to redirect video and audio to HDMI on cc6 SBC with DEY

This is documented in the Linux BSP guide. SBC CC6 documentation can be found here:
http://www.digi.com/support/productdetail?pid=5597&type=documentation

ConnectCore 6 Linux BSP Reference Manual (SBC) : https://www.digi.com/resources/documentation/digidocs/pdfs/90001424.pdf

On dey-image-graphical there are SATO and QT graphical video playback applications.
You can also use gst-launch to customize a gstreamer test pipeline. Some examples follow:
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To reproduce through the HDMI audio with a connected HDMI display:
# gst-launch filesrc location=chieftains.mp3 ! mpegaudioparse ! beepdec ! alsasink card-name=imx-hdmi-soc

Sound
The module can output sound through an external audio chip SGTL5000 on the SBC or through the HDMI interface. 
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The following configuration change will use the HDMI sound card as default:
# echo "defaults.pcm.!card 1" > /etc/asound.conf && sync

Video
Video can be output through the HDMI interface or two LVDS ports.
Device Tree bindings for IPU, framebuffer and LCD display are described at Documentation/devicetree/bindings/fb/fsl_ipuv3_fb.txt.
The current software release only supports a single display. The default device tree configuration enables the HDMI display on mxcfb0, mapping to fb0 for the background plane and fb1 for the overlay plane.

For more details please see ConnectCore 6 Linux BSP Reference Manual (SBC)  referenced above