What bit depth(s) can a video that has an alpha channel have?

[moonman239]

I have a video, and I want it to have an alpha channel. All I know about this video is that the bit depth is 24. My online research tells me that if the bit depth of a video is 24 or 32, then it has an alpha channel. (Sources: 1. http://forums.creativecow.net/thread/2/966297
2. http://apple.stackexchange.com/questions/22818/how-can-i-check-a-video-file-has-an-alpha-channel)

My question is the one I posted in the title, so I'd rather you type something like "An alpha channel can have a bit depth of x, y, or z."

[poisondeathray]

Technically an alpha channel can have any bit depth. But usually use you use the same bit depth as the other channels.

eg. If each channel is 8bpc (bits per channel), and you are working in RGB color model, the bit depth would be 8R+8G+8B+8A = 32 RGBA

Higher end compositing footage and applications typically use 16bpc, so 16+16+16+16 = 64

[moonman239]

Technically an alpha channel can have any bit depth. But usually use you use the same bit depth as the other channels.

eg. If each channel is 8bpc (bits per channel), and you are working in RGB color model, the bit depth would be 8R+8G+8B+8A = 32 RGBA

Higher end compositing footage and applications typically use 16bpc, so 16+16+16+16 = 64

I see.

[poisondeathray]

A more important question is why do you want it to have an alpha channel?