digitalFAQ.com Forum

digitalFAQ.com Forum (http://www.digitalfaq.com/forum/)
-   Capture, Record, Transfer (http://www.digitalfaq.com/forum/video-capture/)
-   -   Decoding VHS RF signal in software? (http://www.digitalfaq.com/forum/video-capture/9432-decoding-vhs-rf.html)

hodgey 02-08-2019 06:01 PM

Decoding VHS RF signal in software?
 
1 Attachment(s)
I thought some of you may be interested in this.

As have been mentioned before on these forums, the people behind the domesday86 project have been working on decoding the rf signal off laserdiscs for a while now. I've restarted work on using the software to do the same with VHS (and maybe other tape formats eventually). It's still very much early stage work in progress, though I got some interesting results already.

Attachment 9556

https://github.com/happycube/ld-decode/issues/16

lordsmurf 02-08-2019 06:20 PM

I don't know what value this has. Explain. :)

Offhand, I have to wonder if access to the "full" signal might allow software-based timebase correction. Other than that (far-fetched?) idea, I'm not sure why it would be done.

For LD, isn't it essentially allowed LD ripping? (True ripping, not "ripping" misused to mean a capture.)

hodgey 02-09-2019 08:31 PM

Software-based timebase correction is indeed one advantage of this, as the decoder will has access to the same signal as a VCR or capture device would. The ld-decode software already does correct the horizontal sync to a degree, but as you can see it's a bit inaccurate on the VHS capture decode as of now. You can also do other stuff like dropout compensation (which is partly implemented for the laserdiscs) as well.

Doing it in software means it doesn't have the limitations of a decoder chip that has to do all this with very limited memory space within a very short time, and it can be tweaked to suit each individual capture in post. Also it means that you are not as reliant on needing the top tier SVHS decks with all the processing bells and whistles, as you are bypassing the player processing entirely.

As for the reasoning behind the project for capturing laserdiscs, you can see the FAQ on their website. I suppose you could use the term ripping, The Domesday discs, and many other laserdiscs utilized some of the unique features of the format to do more than just straight video playback. There is also the fact that Laserdiscs don't store luma and chroma separately like VHS (and other tape formats) so having excellent comb filtering is very crucial, which further complicate capturing the "traditional" way.

latreche34 02-10-2019 01:36 PM

Actually the VHS one is more important than laser disc, very few laser discs didn't make it to DVD or Blu-ray so not much interest there when you can just get the HD version of the movie. But for home videos this sounds like a good ideas with great potential for better quality. Especially if the process involves one digitization only vs 3 with the traditional workflow assuming the line and full frame TBC's are used.

jwillis84 02-10-2019 04:32 PM

This looks like software defined radio in a FPGA chip, driven completely by a firmware upload to the FPGA on boot up. Though I suppose we're getting to the point where CPUs have enough cores and speed to do it by pinning a task off to one part of one core while the rest of the operating system runs on the rest of the CPU.

The trick then becomes one of a proper signal conditioner and an Analog to Digital converter.. which can also be defined in silicon by software.. or as a stock add-on in many system on chip with bundled "peripherals" like the CPU in a cell phone. A CCD camera chip is after all a very simple ADC with many many converters in row and column arrays. Its not like the old days when you needed an analog circuit tied to a photodiode to generate a single "bit" of data.. now you have acres of bits and a flood of digital data to work with in software.

captainvic 02-14-2019 03:03 PM

Quote:

Originally Posted by latreche34 (Post 59310)
Actually the VHS one is more important than laser disc, very few laser discs didn't make it to DVD or Blu-ray so not much interest there when you can just get the HD version of the movie. But for home videos this sounds like a good ideas with great potential for better quality. Especially if the process involves one digitization only vs 3 with the traditional workflow assuming the line and full frame TBC's are used.

Yes, this process could be very important for VHS sources, but to say "very few laser discs didn't make it to DVD or Blu-ray" is not wholly accurate. Approximately 1/3 of my laserdisc collection has yet to be released on DVD or BluRay, probably because most of my laserdiscs are not big-name Hollywood movies.

This process could be important for a variety of analog sources. Thanks for sharing! I find the Domesday Duplicator project to be fascinating.


All times are GMT -5. The time now is 04:57 PM

Site design, images and content © 2002-2019 The Digital FAQ, www.digitalFAQ.com
Forum Software by vBulletin · Copyright © 2019 Jelsoft Enterprises Ltd.