The following applies only to CDN Live services with Push publishing. Please refer to Differences between pull and push publishing for more details. You can customize your publishing URL (also referred as FMS URL) with a CNAME. Please note that publishing URL together with a username and password are used in your live encoder such as FMLE to publish/push its output to the CDN. For the sake of completeness, FMS stands for Flash Media Server and FMLE stands for Flash Media Live Encoder.
How to customize a publishing URL
Let's assume that you have created a CDN Live service with Push publishing and that your publishing URL is rtmp://12345.publishstream.cdnsun.net/P12345. Please note that you can find your publishing URL on the Services/How-To page.
Let's assume that you would like to customize the publishing URL to look similar to publish.mycompany.com.
Add the following DNS record for publish.mycompany.com under your domain name registration.
publish.mycompany.com 3600 IN CNAME 12345.publishstream.cdnsun.net
That's all. Now you can start using rtmp://publish.mycompany.com/P12345 in your live encoder as a publishing (FMS) URL.
Please note that chnages in your DNS configuration may require up to 48 hours for propagation.