Assuming you are talking about a streaming profile (a.k.a. Streaming Quality dropdown list item), here are the steps:
Step 1. Add a custom streaming profile using the user interface.
Step 2. Download a
ui3-local-overrides.js
file via the link at the bottom of UI Settings (requires admin). This file contains a copy of all your current settings, which includes the streaming profiles.
Step 3.
(optional) Open the
ui3-local-overrides.js
file in your favorite text editor and delete everything except the line at the bottom that starts with
OverrideDefaultSetting("ui3_streamingProfileArray",
Step 4. Move the
ui3-local-overrides.js
file to the
ui3
subdirectory of your
Blue Iris installation's web root directory (
www
).