Am335x starter kit is not supporting miracast sink.

Hi,

The AM335X Android 4.2.2 BSP does not support Miracast. Most of the device which supports Miracast are running Kitkat 4.4 or newer:
support.google.com/.../2865484

If you want to add Miracast support you will need to take a look at the AOSP to what they have done to enable support of Miracast for the device, in AOSP it is disable by default:
androidxref.com/.../config.xml

1135 <!-- Whether WiFi display is supported by this device.
1136 There are many prerequisites for this feature to work correctly.
1137 Here are a few of them:
1138 * The WiFi radio must support WiFi P2P.
1139 * The WiFi radio must support concurrent connections to the WiFi display and
1140 to an access point.
1141 * The Audio Flinger audio_policy.conf file must specify a rule for the "r_submix"
1142 remote submix module. This module is used to record and stream system
1143 audio output to the WiFi display encoder in the media server.
1144 * The remote submix module "audio.r_submix.default" must be installed on the device.
1145 * The device must be provisioned with HDCP keys (for protected content).
1146 -->
1147 <bool name="config_enableWifiDisplay">false</bool>