doktor
Posts: 3
Joined: Tue Feb 18, 2014 12:37 am

Using the Raspberry Pi to convert HDMI to composite video?

Tue Feb 18, 2014 12:57 am

Problem:

Have setup a media center with a motherboard which does not output composite video; it can output VGA, or HDMI instead. I would like to add a composite video output to this project, and the Pi has one... there has GOT to be a - relatively inexpensive (CPU wise) - way to use the Pi to output an analog signal from the other computer.

I have heard before of people using VLC to stream their desktop from the computer, and then use the hardware decoding capabilities of the raspberry pi to display it (and therefore solve this problem)... however, I would imagine that streaming your desktop (at a frame-rate and latency acceptable for real-time interaction and video viewing) would create a significant load on my media center computer; I imagine it would work, but it would really bog down the system (only a core-i3 with integrated graphics).

Proposed angle for solution:

- The media center motherboard supports HDMI output...
- Raspberry Pi supports hardware HDMI video decoding, and we know it works pretty well.

...is there some way that the data being sent over the HDMI cable can be recieved by the Pi, and decoded using hardware? This way, hardware on both the media center and Pi sides are doing the heavy lifting (as opposed to using software encoding to stream the output of the media center), creating minimal load. Similarly, is there any way that I can take any of the video outputs from the media center, and somehow receive/decode them with the Pi? If not HDMI, then perhaps VGA?

Also, I have heard of people using HDMI over ethernet... is it possible that I could get an HDMI->ethernet adaptor, run the ethernet cable to the Pi, and then hardware decode it? Or is the video coming in over the HDMI output a completely unsupported format?

Or... is a software approach actually viable? Any discussion is appreciated, and thanks in advance! ;)

ceteras
Posts: 239
Joined: Fri Jan 27, 2012 1:42 pm
Location: Romania

Re: Using the Raspberry Pi to convert HDMI to composite vide

Tue Feb 18, 2014 9:28 am

Why not use a dedicated device to convert HDMI to composite?
Like this $29 http://www.amazon.com/Etekcity%C2%AE-Co ... B008FO7PQA .

ghans
Posts: 7868
Joined: Mon Dec 12, 2011 8:30 pm
Location: Germany

Re: Using the Raspberry Pi to convert HDMI to composite vide

Tue Feb 18, 2014 9:41 am

1) The Pi has no video input .
2) If you are using the Network , you are using USB , which stresses the CPU and has quite a bit of latency compared
to the dedicated GPU hardware and buses.

In short , there is no way to do what you want except living with the latency of Miracast / Airplay Mirroring / traditional Screencasting / remote desktop solutions (yuck !) etc.
Another approach would be simply using your HTPC as media server instead.


ghans
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jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23083
Joined: Sat Jul 30, 2011 7:41 pm

Re: Using the Raspberry Pi to convert HDMI to composite vide

Tue Feb 18, 2014 9:42 am

doktor wrote:Problem:

Have setup a media center with a motherboard which does not output composite video; it can output VGA, or HDMI instead. I would like to add a composite video output to this project, and the Pi has one... there has GOT to be a - relatively inexpensive (CPU wise) - way to use the Pi to output an analog signal from the other computer.

I have heard before of people using VLC to stream their desktop from the computer, and then use the hardware decoding capabilities of the raspberry pi to display it (and therefore solve this problem)... however, I would imagine that streaming your desktop (at a frame-rate and latency acceptable for real-time interaction and video viewing) would create a significant load on my media center computer; I imagine it would work, but it would really bog down the system (only a core-i3 with integrated graphics).

Proposed angle for solution:

- The media center motherboard supports HDMI output...
- Raspberry Pi supports hardware HDMI video decoding, and we know it works pretty well.

...is there some way that the data being sent over the HDMI cable can be recieved by the Pi, and decoded using hardware? This way, hardware on both the media center and Pi sides are doing the heavy lifting (as opposed to using software encoding to stream the output of the media center), creating minimal load. Similarly, is there any way that I can take any of the video outputs from the media center, and somehow receive/decode them with the Pi? If not HDMI, then perhaps VGA?

Also, I have heard of people using HDMI over ethernet... is it possible that I could get an HDMI->ethernet adaptor, run the ethernet cable to the Pi, and then hardware decode it? Or is the video coming in over the HDMI output a completely unsupported format?

Or... is a software approach actually viable? Any discussion is appreciated, and thanks in advance! ;)
The Pi doesn't support HDMI decoding. There is no HDMI in, just HDMI out.

There is a prototype HDMI in Add-on board, but that is not for sale at this point.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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wimble
Posts: 34
Joined: Tue Feb 05, 2013 9:52 am

Re: Using the Raspberry Pi to convert HDMI to composite vide

Tue Feb 18, 2014 10:26 am

Why not install OpenElec on the Pi and use it directly as a media player, accessing the files from your PC across the network (rather than having the PC decode them to video)?

doktor
Posts: 3
Joined: Tue Feb 18, 2014 12:37 am

Re: Using the Raspberry Pi to convert HDMI to composite vide

Tue Feb 18, 2014 1:56 pm

Ok, I'll admit it: I'm confused... I'm a programmer by profession, and honestly know nothing about HDMI and media encoding/decoding in general. I thought that the Pi had H.264 hardware decoding, and that maybe the video data could be passed across the HDMI cable in that format. Finally, I thought that MAYBE it would be possible to turn down the clock on the HDMI data transfer, and convert it over to an ethernet cable, and run it in to the Pi... But this just shows you how little I actually understand with regards to world of hardware :P

1. The media center computer utilizes integrated graphics processing to output the screen (normally) to HDMI or VGA... is there any way to get it to output the screen over ethernet - preferably using the hardware resources it uses for normal screen output?

2. Would disabling the display on the media center free up resources that would make screen sharing more feasible (as I don't need a display)?

Ghans:

I've actually been doing this for the past few months (using OpenElec on Pi, and streaming from my beastly desktop); I'm just not quite satisfied with the speed, and also the features that I am restricted to because of the speed. I am impressed overall with the Pi, and it does work, albeit quite slowly.

You have me thinking though... WHAT if I did all the intensive processing (heavy lifting) on my media center computer, and then simply displayed menu states and played videos on the Pi (sort of like hybrid computed-streamed screen sharing).

For example, the user opens the Prime Wire add-on for XBMC, and searches for a movie: The search and all computing would be done on the media center computer, then the results and applicable data would be sent via ethernet connection to the Pi, and the Pi would display the results!

Has anyone done something like this before? This seems like it could work, and would likely work much better then simply screen sharing... Plus, it would give me a fun excuse to begin a new programming project and learn about developing with the XBMC software :)

doktor
Posts: 3
Joined: Tue Feb 18, 2014 12:37 am

Re: Using the Raspberry Pi to convert HDMI to composite vide

Tue Feb 18, 2014 2:05 pm

Or, if i were to distribute the computing like I mentioned above... is there a faster way to connect the media center computer with the Pi and communicate (then ethernet)? Or would ethernet suffice for a scheme like this? Obviously, it seems it would end up coming down to how crafty I am with coding how the work is distributed...

ghans
Posts: 7868
Joined: Mon Dec 12, 2011 8:30 pm
Location: Germany

Re: Using the Raspberry Pi to convert HDMI to composite vide

Tue Feb 18, 2014 3:06 pm

HDMI is uncompressed video data. The cables have a bandwidth
of 2-4 Gbits per second at least ! There is no way sending
that over a 100 Mb/s IP network without compression. This
automatically incurs IP and encoding latency. This is the
fundamental problem with OnLive and Airplay Mirroring. So
far i know Miracast tries to tackle this by having a special
physical layer (WiFi Direct).

What i and wimble have hinted at is to use the HTPC as server
instead. The server sends encoded data , and the Pi handles
playback in full HD - this has no latency because the screen
content hasn't to be copied across the whole network
but is rendered/decoded by the Pi directly .
Search for DLNA/UPnP.

Another approach is to setup XBMC to share one database. You
have to use XBMC on the HTPC and the Pi , and the machines
share all info like last played files , last state , settings and
more. Check the XBMC wiki - it is a bit more complicated than
simple DLNA sharing.

All your proposed approaches are already used by Miracast and
similiar protocols i listed. If you can get them running on your
HTPC and your Pi (hint : you propably won't , i
boldly predict) , you will have to live with their limitations i
outlined.

PS: ceteras solution might be the most sensible thing to do
for the time being.


ghans
• Don't like the board ? Missing features ? Change to the prosilver theme ! You can find it in your settings.
• Don't like to search the forum BEFORE posting 'cos it's useless ? Try googling : yoursearchtermshere site:raspberrypi.org

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