Digital TV Transmitter Using a VGA card

An anonymous reader writes "Yet Another Project from Fabrice Bellard : with any PC and a standard VGA card, you can build a real Analog or DVB-T Digital TV transmitter by directly generating the VHF signal. The provided example shows a Lena picture transmitted as a real Digital TV channel."

Comments

Now lets get some NTSC

[ankhcraft]

Once someone posts how to do this with NTSC (which you'll need if you're in the U.S. like me), I'll be all over this! Anyone? Enlighten me...

Re:Now lets get some NTSC

[b1t r0t]

Oh gee whiz... I think I figured it out now. What he did was make a grayscale image that resulted in a signal which was equivalent the unmodulated data stream. So the VGA card was esentially being used as an enormous shift register. In that case, it would definitely take some work (and an 8VSB modulator) to make it generate ATSC.

Has been done with music for a while

[m50d]

There's an X program that can transmit an MP3 to your radio by displaying pictures in certain ways. Quality's not too good, but it works. I guess it was just a matter of time before people did it with television.

It also goes to show TEMPEST attacks are real. Your screen is transmitting what's on it in a way that's detectable over quite a distance. Shielding is worth looking at if you're doing something sensitive.

Re:Has been done with music for a while

[Rei]

You're talking about Tempest For Eliza". I never got the "broadcast an mp3" function to work, however - only the broadcast using their special midi-like files. A shame, really. Still, even the midi-like broadcasts make for a neat geeky party trick, and demonstrate the power of tempest ;)

Re:ANOTHER one!!

[gg3po]

I know he's the guy behind ffmpeg (used by most *nix media players) and the excellent qemu emulator that I use every day.

The Lenna Story.

[British]

....is more interesting than the main one. At my company when I started 6 years ago, I stumbled upon the Lenna picture, just thinking it was an ordinary pic. Few years later I saw the er, um "full" pictures. Didn't know she had a cult following.

Yes, that Lenna picture I assure you is still in use after all these years. A pretty "hello world" image.

Re:The Lenna Story.

[kureido]

Lenna is one of the many "standardized" images used in image processing research, akin to the well-understood strains of Norway rats used by medical researchers all over the world so that their peers can reproduce their experiments. For more examples of standard research images, see the USC-SIPI image database.

crap ..

[macaulay805]

I clicked on the link while I was at work, now I'm waiting for the network security people to remove me from my workstation.

On a side note: WARNINGS PLEASE!

ATV

[leighklotz]

You can do ATV legally in the US with NTSC, with a ham license.

You can see this the video for yourself, with stuff you have at home right now. There are cable channels that are on ham bands, but it's OK because their signals stay on the cable.

If you live in the SF ba area, hook a UHF antenna (vertically polarized) to your cable-ready TV or VCR with TV out, and tune to cable channel 57 (421.25 MHz), and aim it at Mt. Hamilton (east of San Jose).

Here are some tests on 1.2GHz, which is also a ham band.

Guerrilla television in 2007

[Simonetta]

I suspect we may start to see illegal broadcasts in 2007 in poorer urban neighborhoods of the USA.

With all broadcast television on VHF/UHF scheduled to cease on New Years Day 2007, there are going to be a lot of pissed off people who don't have cable getting nothing but static on every channel.

This is assuming that UHF/VHF broadcasting actually does go off the air Jan 1, 2007. It doesn't seem likely at this time, but it is mandated by the TeleCom Act of 1996. And one never knows what the current administration is going to do.

Let's assume that it does happen. All the middle-class people won't notice it because they are paying monthly cable fees and cable TV will not be affected by the VHF/UHF shutdown. However, let's assume that in poor neighborhoods the convertor boxes don't work well, or are prohibitively expensive, or are too technically complex for the general population. Suddenly there's no television.

Well politics abhors a vacuum. We may find ourselves in a situation where people simply start pirate broadcasting on the unused television channels. This will probably cause problems with the new uses of the spectrum (private cell phone communications, I believe). The FCC will be really busy trying to track down pirate TV stations. Pirate TV stations are rare now because they can't compete with broadcast network quality, and there are outlets on local cable access for speciality and non-professional broadcasters.

But with the UHF/VHF channels gone off the air, people will start filling it up with DVD broadcasts. Maybe even porn broadcasts. Unregulated, and without commercials. All illegal.

These channels could become political if there is an economic downturn or a return of conscription into the permanent, endless war that the administration has promised the defense contractors and campaign contributors. Alternative broadcasts of police beatings at demonstrations made by tiny CamCorders alternating with current Hollywood movies downloaded from the DarkWeb could become common content on the new pirate channels.

I wonder if anyone is considering the possibility of this happening before they decide to shut down UHF/VHF broadcasting in 2007?

Re:Guerrilla television in 2007

[antrik]

Sorry for disspelling your very original fantasies... but nothing of that kind seems to be happening here in Berlin, where they did shut down analog TV broadcasts some two years ago.

The frequencies are reused for the new digital broadcasting -- there are now about five times as much stations available, and posing a considerable threat to cable television: As cable is still analog, you get the same number of channels in a better quality for free on air... Only thing you need to pay is buying the receiver (< $100) once.

Guys, this is no small feat

[o'reor]

and yes, I am a (former) DVB-T engineer (and a consultant in digital video broadcasting at large -- yes, I know a bit about the US and Japanese standards too).

What Fabrice is telling us here is that he has managed to produce a real-time (or close-to-real-time) DVB-T/DVB-H software COFDM modulator, the output of which may be broadcast via the DAC converters of the video board. Given the complexity of the generated signal (more than 6000 subcarriers, not including pilot subcarriers which are used as beacons for the demodulator, and paying respect to the guard interval -- sorry for the technical gobbledygook), this usually requires a dedicated ASIC. Don't forget to include the preliminary phases of the encoding : creating an MPEG-2 video channel, an MEPG-2 transport stream (OK, he did it using a modified MPEG library), then encapsulate this into MPEG-2/DVB frames, add the Reed-Solomon code, perform the interleaving procedure, pour in some Viterbi encoding for redundancy, and feed it to the input of the DVB-T modulator, phew ! you're done.

I want to say hats off, ladies and gentlemen, to this outstanding performance. The Free Software movement definitely needs more guys like Fabrice, and we all need to encourage him into publishing more of his code.

Chapeau bas, mon cher Fabrice !

Re:Guys, this is no small feat

[Anonymous Coward]

It's not realtime. He's rendering to a PGM file, and then by displaying it. Not easy, but it's not a replacement for custom hardware.