We recommend streaming on Bandcamp via OBS, as it's free and fairly easy to use, but also deeply configurable.
The first thing to do is to set the default audio input device. Click "Settings" in the bottom right corner. Select the "Audio" pane. Under "Devices" use the "Mic / Auxiliary Audio" dropdown to select your audio device, whether it’s your USB mixer, audio interface or USB microphone. In this example, it’s a Scarlett 4i4 USB interface:
Now when you make noise, the "Mic/Aux" meter in the middle of OBS at the bottom should light up.
Adjust the volume there if needed, but in the case of an interface or mixer, keep in mind you can also adjust the volume of the inputs on the device itself. Try to avoid going into the red zone as this will cause distortion.
Next you need to set up your video source. First, ensure your canvas is set to a 16:9 ratio by going to "Settings" in the bottom right of OBS, clicking "Video" and choosing a Base (Canvas) Resolution that shows "Aspect Ratio 16:9" next to the dropdown, for example "1920x1080" or "1280x720". Also ensure your Output (Scaled) Resolution also shows as "Aspect Ratio 16:9". You can do this by choosing "1280x720" in the dropdown. Click "OK" to return to the main OBS window.
In the bottom left of the "Sources" pane, click the "+" button. A number of options will pop up:
Select "Video Capture Device" and a dialog will appear asking you to name this source. Name it something useful like "Webcam" or "Camera 1". Click "OK".
Select your video input from the Device dropdown. Here, we’re using a Logitech BRIO webcam, but it could be "FaceTime HD Camera". Just ensure the preview shows the video feed you want to use before clicking "OK".
Your video source should now be displayed on your OBS window. It has a red border around it, which means you can resize or reposition it on the canvas.
Resize the video source to fill the canvas, as by default it may be a different size. Depending on the aspect ratio of your camera, it may need to be cropped slightly.
When you’re done positioning the video, you can click the "🔓" icon next to it in Sources, which prevents you from accidentally moving it.
You can also set up scenes in OBS, to allow you to quickly switch between different configurations. Read more about that here.
When you are confident that OBS is set up and you are ready to perform, you can create your Bandcamp livestream via the "+ add" menu in the navigation bar to get testing.