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HDTV via GNU Radio
NortonDC writes "High Definition TV has been successfully captured in its native data stream from an over the air broadcast by a software defined radio that is Free and open source from the GNU Software Defined Radio project."
GNU TV, where the scripts are open-sourced before the show airs and you know all the jokes before the intro starts rolling.
Mind you, if you knew when to cringe in Nerds (the competitor to Friends, where housebound geeks spend their days in an eternal LAN party with the occasional visit to the pizza parlour) at the "jokes", it mightn't be so bad...
-Mark
Sounds too useful to exist.
It will taste the blade of DMCA before the end of the month.
Why am I looking at 4MB images of Lenny Briscoe?
HDTV is either 1920x1080 (1080i) or 1280x720 (720p). Where did the 2730x1088 resolution come from? It's obviously wrong (the images are obviously scrunched vertically).
Seems really neat, but I found that card on a science site. ONLY 1000 pounds (Great Britan). I suspect that this isn't much cheaper in the US either ;-(
. js p?action=GetProduct&pid=91&sid=1
https://directory.adeptscience.co.uk/controller
The images on the site are at 2740x1088 resolution, but HDTV at max resolution is 1920x1080. You can tell from looking at the images that they're horizontally stretched, so something weird is going on.
A Linux-friendly HDTV recording solution is definitely needed. Unfortunately, it seems that in order to record HDTV you need a $1300 Analog Input Board.
Can anyone with more knowledge about this project please post a less expensive solution if one exists?
If I am reading it correctly, they used a special radio card under Linux to capture radio waves. Then they ran those waves through a piece of software that could decode them into video, because the waves they tuned into were an HDTV broadcast. The difference here is that they simply record the wave, it's not decoded in hardware. This way they can ues the same card to get FM, AM, HDTV, VHF, UHF, or whatever (in theory). Anyone actually know the answer to this question?
Comment forecast: Bits of genius surrounded by a sea of mediocrity.
You can get many TV shows you might have missed by using BitTorrent .
This site has a list of links to various sites which contain TV shows available through BitTorrent.
A West Wing episode is available here (The West Wing - s04e16 - California 47th [ftv].mpg.torrent) (but you need to have installed BitTorrent prior to clicking on that link).
I don't follow West Wing so I don't know whether that's from second season, and your comment is accurate -- that's the only one available from that site. One other is The.West.Wing.S04E14.Inauguration.Day.Part.I .
Enjoy!
I feel fantastic, and I'm still alive.
5 -- You think a $3,500 computer with a 17 inch monitor is better than a $2,000 HDTV set with a 35 inch screen
4 -- You wanna take screenshots of Joe Millionaire and set them as your desktop wallpaper
3 -- You're unemployed and have nothing else to do aside from incessant blogging
2 -- Regular TV is _so_ '90s.
1 -- Record Cinemax skin flicks as part of the Masturbate For Peace campaign
Courtesy of The *nix Top 5
Reply or e-mail; don't vaguely moderate. Ex-O'Reilly/MIT employee, now a full-time Google employee.
At $1,299.00 for the PCI card that their driver is written for, I do not see this in my future. For that matter, I don't see that in the future of many hobbiests which makes this project rather useless to the general population at present.
See here for information on the product the GNU Radio project wrote the driver for: Measurement Computing
Maybe some day...
My understanding is that it is a fight against copy protection. Open (Free) software defined radio means that the user can pull down any (unencrypted) broadcast and save it - whether or not the "broadcast flag" (no-copy bit) has been used. In a future in which hardware televisions can't save copies of anything, this will allow the user to save copies and play back later (or do anything else) on a future PC or TiVo. Good stuff.
sulli
RTFJ.
Man, I wish the Gnu folks would build their own hardware card rather than the card they are currently using - it's quite expensive.
I'd love to see them put a decent FPGA, an Intersil 50216 4 channel digital downconverter, and a nice 60 Msample/sec 12 bit flash A/D converter on the card - they could do that for a bill of materials of about US$200, and have enough power to do the capture properly.
Before you say "Fine - why don't YOU design it?": I'd love to get more involved in GnuRadio, but I'm afraid of potential conflicts of interest both ways - contaminating GnuRadio with my professional work and possibly exposing my employer to problems with GPL infringment.
Also, is anybody big in the Gnu Radio project going to be at IWCE (International Wireless Convenention and Exposition) March 10 - 14? If so, where? I'm getting in on an exhibitor's badge - maybe I could get pictures?
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It's not so much a special radio card as it is just any wide-banded data acquisition board and a little frequency-translation unit.
There is a "tuner" that multiplies the incoming radio signals by a variable frequency. When you mix two oscillating signals (by multiplication) you get harmonics. If the variable frequency is just a sine wave (i.e., not modulated with any information), then the harmonics are identical in modulation to the original, but at a difference frequency. The tuning box is used to bring various radio signals down to a frequency that can be digitized by any ordinary data acquisition board.
These data acquisition boards are designed to basically sample voltages of whatever is tied to their inputs, and to sample it very very quickly and very often. Since these boards (and computers also) are getting more advanced (i.e. faster), they are able to sample real radio frequencies (stuff in the ones of MHz ranges).
After you get the signal digitized, it's just a simple matter of writing software that mathematically performs the functions that all the circuitry in the 'old-fashioned' receivers would do with their capacitors, resistors, and inductors (and more).
That's pretty much how it works.
a little expensive for my taste.
Always going forward, 'cause we can't find reverse.
Bascially the aim is to drastically decrease cost and increase flexibility of radio signal reception and decoding by replacing lots of specialized electronics with software.
Now instead of a very expensive ATSC decoder for your HDTV-Ready TV, you will now have a box with an antenna, maybe a preamp, and a powerful DSP running in software.
The cool part is, you can reprogram or adjust the software as needed to create other capabilities, use other frequencies, or increase performance even after the product is shipped.
I'm sure I drastically oversimplified this, and probably don't realize the full scope of the benifits. Read up on it, use google.
But as applied to HDTV, this is an AMAZING accomplishment. We might soon have open-source HDTV decoding. I for one, would love to have the ability to directly access the native format of the TV signal, stream it to disk, multicast it on my home lan to the living room, whatever. COOL STUFF!
GNU Radio is a collection of software that when combined with minimal hardware, allows the construction of radios where the actual waveforms transmitted and received are defined by software. What this means is that it turns the digital modulation schemes used in today's high performance wireless devices into software problems.
Read the site! This is very important stuff and could have a huge impact on technology.Try one of the GNU mirrors:
e s/hdtv-samples.html
s amples.html
e s/hdtv-samples.html
a ges/hdtv-samples.html
: www.gnu.org/server/list-mirrors.html+gnu.org+mirro rs&hl=en&ie=UTF-8
http://gnu.sunsite.utk.edu/software/gnuradio/imag
http://gnu.wwc.edu/software/gnuradio/images/hdtv-
http://gnu.mscnetworks.com/software/gnuradio/imag
http://www.phildowd.com:4060/software/gnuradio/im
Basically, append software/gnuradio/images/hdtv-samples.html to any of the links from here: http://216.239.57.100/search?q=cache:1KyAbWv9nRAC
Withdrawal before climax is very ineffective and those who try this are usually called "parents."
It could be used for that (assuming you have a way to rebroadcast the signal later? Without the FCC hunting your signal down?), but the purpose of the software is to provide signal-processing software targeted at radio signal processing. If that signal is an HDTV signal, than so be it, but it could just as easily be X-Ray signals from space (assuming your sampling device could capture them) or some AM Radio talk show.
If you look at the site you can see a number of other examples. Since you are no longer limited by a standard radio's hardware, you can do completely different stuff like receive two different frequencies at the same time.
If I have been able to see further than others, it is because I bought a pair of binoculars.
This has been covered here on Slashdot before. Some of the comments in the previous post are particularily informative.
Always value the individual over the system. --Bruce Lee "I don't need a Sig - I have a custom 191" - me
A few nitpicks:
.7 volts a 6 or a 5?), and you have to slice at the correct time (the symbols are only defined at certain times - any other time the signal isn't valid, it is a blend of the current and the (next|previous) symbol - what is called inter-symbol interference or ISI). So you have to do symbol tracking - figuring out when to sample, and at what levels to slice.
You don't get harmonics (frequencies that are related to the fundimental by an integer multiple), you get mixing products, also known as "sum and difference".
You get harmonics when you feed a single signal into a non-linear element - feed f1 in, get f1, 2*f1, 3*f1, 4*f1,... out. This is commonly used in tranmsitters to allow the use of a lower-frequency crystal to generate higher frequency carriers - you use a 10 MHz crystal, and the feed it into a non-linear element such as a squaring amp, and pick off the tenth harmonic to get 100 MHz.
Mixing involves feeding 2 signals f1 and f2 into a multiplier - you get f1, f2, f1-f2, and f1+f2 out. Mixing allows changing a frequency by a non-integer relationship. You have heard this used in the voice distorters used on TV to mask mob informants - they mix the person's voice with a low-frequency signal to change the pitch of the speaker's voice. This is also the basis of any modern superheterodyne receiver - you mix two different (heterogenous) signals together.
The idea is to take the signal from whatever frequency it is on, and move it to the frequency you have designed your circuit to work at - an "intermediate frequency", or IF. You then filter the signal, amplify it to a specified level, and repeat as necessary to get the signal where you want it. For example, a standard FM radio might go from the broadcast frequency to a 10.7 MHz first IF, then to a 455 kHz second IF, then finally to the FM detector circuit.
Eventually, in a design like GnuRadio, you sample the signal. The tricky bit is you have to sample at a frequency not less than twice the highest bandwidth in the signal (Nyquist's criterion). For a 6MHz wide TV signal, that means you need to sample at not less than 12 million samples per second.
Then, for a system like HDTV, you are dealing with a complex signal - and I mean complex as in sqrt(-1), not just as in "not simple" - you need both the real (in-phase, or I signal - the "real" part) and the quadrature (out-of-phase, or Q signal - the imaginary part). The signal is 8VSB - eight level vestigial sideband. So you have to do carrier recovery and tracking (because the carrier itself was removed - that is what makes it a sideband signal), then you have to convert the signals from the analog RF signal into one of 8 levels (slicing is the technical term). However, you have to slice accurately in 2 dimensions - you have to slice at the correct level (is
Finally, once you have a symbol stream, you then have to do all the foward error correction - you have to de-interleave the signal (think of unshuffling a deck of cards) - interleaving is done so that a transient interference (like a lightning strike) doesn't scramble adjacent bits - the errors are spread out.
Then you do your block error correction - this can undo a small number of bit errors per block (again, that's why you interleave the signal: so that block error correction needs to only correct a few bit errors per block).
Then you do some more protocol recovery, and you have an MPEG stream.
Normally, you do this sort of stuff with a big FPGA or an ASIC. The GnuRadio folks are doing it in software. The up side is that you can more easily tweak the code. The downside is that you are not going to be real-time for a few more iterations of Moore's "Law".
What gets to be REALLY fun is when, in addition to all of the above, you have to compute parametrics on the signal - not just recover the bits, but measure how far out of ideal the signal was (that's the sort of stuff I do for a living.) When you do that, you have to do all of the above, THEN once you have an error corrected bit stream you have to regenerate an ideal signal and compare the received signal against it, and measure how far away from the ideal signal the real signal is.
And THAT is when you start using multi-GHz processors, 10 million gate FPGAs, big-ass DSPs, and all sorts of other fun stuff.
www.eFax.com are spammers
Also, keep in mind that the popular CRT and projection projection TVs will purposily overscan the picture such that some of the lines are pushed outside of the viewing area. So, while 1088 lines are broadcast, a projection TV may only show 1076 of them and clip 6 lines each from top and bottom. If overscanning results in only 4 lines being clipped then you will actually see only 1080 of the 1088 lines of MPEG-2 stream.
The width of 2730 pixels appears to be intended get close to the correct aspect ratio when displayed on a computer monitor. Based on how the people's heads look on my monitor, it seems to be a little over stretched. But when I return the images to 1920x1088, they clearly look squeezed.
Actually, 20MHz isn't so bad - I work with 40 Msample/sec 12-bit flash converters, and there are 100 Msample/sec 12-bit flash converters on the market.
However, you DON'T build things like this with your brother's wood-burning kit and a old nail - These parts come in surface mount packages, and your board has to be carefully designed to maintain proper impedance matching on the RF traces, as well as having excellent grounding (RF and digital grounds meeting at one and only one point, ground planes cut as needed to prevent current loops, etc.).
Lastly, you need a proper dithering circuit to introduce noise equivelent to 1/2 of the least significant bit, in order to shape the quantization noise out of the frequencies of interest. Otherwise, you end up throwing away a couple of bits of resolution.
Those are the sorts of things you have top-notch RF designers laying out, and a top-notch fab build for you - either by having such a fab working for you, or by contracting it out.
www.eFax.com are spammers
Maybe it *will* be illegal in your country.
.au care to comment on the current digital transmissions?
But eventually Supply and Demand will kick in - someone will want to tape "Friends, 2009", so presto! the means will appear. Soon enough you'll be able to buy the equivalent HDTV VCR from China for $120 that "mistakenly" ignores the broadcast flag, a-la DVD zoning.
Pity it means that some other country's tech industry gets the "3) Profit!".
Side note:
Sure won't be worrying about how illegal it is in my country (Australia) for a long while yet.
Is "the switch" happening in 2008? And have we sorted whether we're going for SDTV or HDTV?
Anyone with a set-top DTV box in
Anyone? Anyone? Bueller?
You are in a twisty maze of processor lines, all alike.
There is a lot of hype here.
Gnu are not gnu/funny.
[FUCK BETA]