Revisiting The SlimPort Output Of Android Devices

A few days back I received a G+ IM from someone who had discovered my description of how to use an HDMI splitter to make the output of an Android tablet more useful. He posed a question that I think is worth sharing. He asked the following;

Dear Michael,

I just read your article about capturing video from a Nexus 7 and I have a question about that if you do not mind.

I bought a Nexus 7 (2013) to be able to give presentations and show short movies in my classroom. The thing is that most projectors still have only a VGA socket. I have a cable Slimport=>HDMI and it works perfectly well.

I also have a cable HDMI=>VGA but it does not work and I suspect it is because of the HDCP. I was wondering if the splitter and HDCP stripper you used could work in my case. If yes that would be great and would literally save my classes.

Thank your for your time and sorry again to bother you with that.

Thibaut Bailly

To begin, as a blogger, I welcome questions from readers. For the most part people blog because the want to share what they’ve discovered. As a non-professional blogger I may not always respond immediately, but I try to respond to every comment and question.

When connected to an HDTV, or even computer monitor with an HDMI input, the Android device is able to perform a proper HDCP handshake so it enables it’s output.

If you adapt the HDMI output to VGA then there’s no way for the display device to address the HDCP issue. The VGA connection is not a “smart” or “negotiated” connection, it passes only video. Lacking for HDCP handshake the Android device will not enable it’s video output. Full stop. Have a nice day.

As I described previously, you can make use of an HDMI splitter, and a second monitor to enable your VGA connection to the splitter. The important part is that one outputs of the HDMI splitter must be connected to a bone fide HDTV or monitor via HDMI. That satisfies the HDCP handshake so that the tablet will enable its output.

Then the second splitter output allows you to take the output stream to whatever other display or capture device you desire. Thus you can use an HDMI-to-VGA adapter to feed your projector.

While the security provisions that are HDCP may now be satisfied, there remains some potential complexity with respect to display resolution. It’s true that many existing projectors rely primarily upon a VGA connector. It’s also true that such projectors don’t usually support output resolutions as high as are now commonplace with LCD displays. Your Nexus7 delivers 1080p60 via the Slimport adapter, which may cause your projector to complain about the signal as out of its display range.

If the video source was a computer you might just set the output resolutions to something lesser that the projector would accept. The Nexus 7 doesn’t readily allow that as far as I know. However, the HDMI connection is a smart path, that will negotiate a lower resolution if the HDMI connected display ask for such.

If you can find a slightly smaller, older or cheaper, monitor or TV that has 720p native resolution, your Nexus will downshift to delivering a 1280×720 pixel stream. That may be more satisfactory to your projector.

I replied to the reader’s question via IM, since that was where it was originally posed, although there’s a bit more detail provided here.