HDMI In

I have started several hobby / learning experiments with HDMI. I never had sufficient practical knowledge of the standard and my curiosity angle has been security / copy protection. I could never imagined an offline system capable of securing digital content. In the end this content must be terminated somewhere (the TV display panel) in an unencrypted form and then could be reassembled again with any encryption removed.

Extending this logic, you could  envision a pass-through digital device which emulates the display panel, presenting itself as a secure rendering device to the content source and then relaying the digital stream further out.

I started my experiments by finding a flexible platform capable of accepting HDMI input. It turns out the Realtek RTD1295 SoC is the important part. And the Zidoo Z9S TV box is probably the lowest cost implementation offering HDMI In feature: "Unique HDMI IN 2.0 port, and able to achieve PIP and support recording function". I found one for ~$80.

I hooked it to my TV, feeding the output of the Apple TV to the Zidoo's HDMI In port. It all worked seamlessly. The Apple TV output appeared in a small window which could be maximized to full-screen. Zidoo has a "recording" function which captures the HDMI stream to an MP4 file. The nice thing is that the box supports NTFS, so can produce long (more than 4GB) files, which helps managing the captured content. 

As expected, while the Zidoo box was capturing nicely the Apple TV "menu" operation, it refused to record protected streaming content. My experiment continued plugging a $30 HDMI Matrix switch in between. I was always intrigued by how these matrix switches worked. The one I tried has 4 inputs and 2 outputs and can connect any input to any output. Including an option to fork an input source to two outputs. How does copy protection work in such case? Well... it turns out it does not... The matrix switch terminates the input stream and regenerates it on the output, with the net effect being the recording function on the HDMI In box never complains about the input stream.

Which brings me to the expected conclusion - HDMI copy protection does nothing to prevent bad guys from hijacking the digital content. It is also known to create several issues for legitimate users. To be honest I have no idea why companies bother mandating and implementing security schemes which are completely ineffective....