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Guest
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 13 Oct 2013, 07:47 |
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Best of luck on this. Hope good progress and improvements are made.
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publius
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 02 Nov 2013, 18:20 |
Hardcore fan |
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Joined: 23 Sep 2003, 18:14 Posts: 1391 Location: United States Has thanked: 39 times Been thanked: 21 times
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happycube wrote: I'm starting to look at the AC3 encoding - I think i can probably figure out QPSK, but it doesn't look like the patent has enough information on how to handle the error correction coding etc needed to get an actual AC3 bitstream. And I don't have a decoder that I can use to get reference data. The ATSC A53 document has much more complete reference information on AC3 than the patents.
_________________ MUSE decoder information and user guides LD player connexion guide
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Guest
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 18 Nov 2013, 12:08 |
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You may or may not already know and be doing this... But laserdisc has TOC (table of contents), frame number, closed captions, and other info stored on un-visible NTSC lines. NTSC has 525 lines all together and I'm hoping that's what you're trying to process. Here's a quote from MAME author Aaron Giles: Quote: I discovered that there was something missing in all existing laserdisc captures. If you know anything about the NTSC broadcast standard, you know that a video signal consists of 525 scanlines spread across a 30Hz (actually 29.97Hz) interval. Of those 525 scanlines, 480 are considered to be "visible" scanlines, while the remaining 45 constitute the vertical blanking interval (VBI). He basically states there's information on the video signal that's visible, provided you capture all 525 lines of resolution. When playing back the video you can do whatever is required with the extra picture (looks like noise but it can be converted to digital binary form); all that's needed is capturing all 525 lines of NTSC reolution. Most of this data is probably more useful for CAV laserdiscs and videogame laserdiscs, but I think it's still worth doing even for the most basic CLV laserdiscs (even if it seems redundant). Another quote (Aaron Giles): Quote: Below is a picture of the VBI region for a CAV laserdisc. The top few rows are an ugly green because those lines of VBI data were not provided by the capture card. The remaining lines show what the white flag and Manchester-encoded Philips codes look like: Here's links with more info in case you haven't already read it and want to understand more of it (hopefully!): http://aarongiles.com/?m=200807http://aarongiles.com/?m=200808Think the biggest problem with Laserdisc players is the composite encoding quality. Quality differs greatly from player to player and colors can be completely wrong; this is probably mostly on 80's to early 90's players. Composite quality on a modern VHS deck (2000 or newer) will jump big time vs an early 90's to 80's model for example, and I think you can get RGB like quality with dscaler or v4lctl with newer composite devices. It's a shame RGB wasn't used in the states like in Europe (marketing over quality takes the lead in the states it seems). Here's an example of what I mean (composite Laserdisc left; DVD right; courtesy of evildragon) REMOVED due to bad example [url][/url]):A software image decoder for laserdisc could alleviate these hardware problems.
Last edited by Guest on 20 Mar 2014, 19:40, edited 2 times in total.
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happycube
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 28 Nov 2013, 20:25 |
Absolute fan |
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Joined: 18 Apr 2012, 18:02 Posts: 1614 Location: United States Has thanked: 71 times Been thanked: 88 times
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I've already handled the white flag... and I think the Lion King did have blue in it, a lot of Disney DVD's are known to have altered color. It took me a long time to realize the capture setup I have glitches. I thought it was a player glitch until I realized that each one was exactly 2K long, and pulls in data from earlier. There's some sort of sync issue with the data capture itself... I want to figure out a cheap way to capture the analog data over USB anyway so it's easier to reproduce, but I haven't figured out how yet. Ideally there'd be an affordable USB3 ~100mhz ADC, but there isn't yet. I'm thinking something involving a Beaglebone Black might get up to 8fsc/28mhz, but I haven't tried anything yet. In any case, once I have the glitches fixed, I should be capturing and decoding pretty nice video. (edit 11/29/13: Fixed the capture glitches. Also, while trying to work out on what I thought was dropout compensation, I figured how to correct for some of the pre-emphasis stuff. New captures and hopefully video coming soon(tm) )
_________________ Happycube Labs: Where the past is being re-made, today. [meep!]
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happycube
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 07 Dec 2013, 18:53 |
Absolute fan |
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Joined: 18 Apr 2012, 18:02 Posts: 1614 Location: United States Has thanked: 71 times Been thanked: 88 times
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Pre-emphasis is a birch. It's very hard to compensate for correctly... ... and almost every LD player fails to do it quite right. Maybe the X0 does. (and possibly the player Laserdiscmodder re-capped etc - at least he claimed/showed it...) Perhaps when new the PR-7820 did as well, but if it used electrolytics they probably drifted by now. Basically a sharp brightness change is exaggerated/pre-emphasized, and the player needs to de-emphasize it in return. When done properly, this reduces noise since the shifts are reduced. When not done properly, you see ringing once the signal returns to the proper level, and that shift gets de-emphasized as well, even though it shouldn't. This is why you see ringing/ghosting on test patterns.
_________________ Happycube Labs: Where the past is being re-made, today. [meep!]
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happycube
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 15 Dec 2013, 20:47 |
Absolute fan |
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Joined: 18 Apr 2012, 18:02 Posts: 1614 Location: United States Has thanked: 71 times Been thanked: 88 times
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Just posted a test video from an obscure 1981 Pioneer disk, "Rock Adventure" - unfortunately the disk is a bit dirty/rotted, but I wanted to post something that wouldn't set off MPAA lap dogs http://www.youtube.com/watch?v=FYru56W57jA
_________________ Happycube Labs: Where the past is being re-made, today. [meep!]
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Guest
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 03 Jan 2014, 10:04 |
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happycube wrote: Just posted a test video from an obscure 1981 Pioneer disk, "Rock Adventure" - unfortunately the disk is a bit dirty/rotted, but I wanted to post something that wouldn't set off MPAA lap dogs http://www.youtube.com/watch?v=FYru56W57jAWow - looking awesome ! I've unfortunately been very busy in real life the past few months, so haven't made much progress on comb filter decoding, but from the look of things you are almost done !
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happycube
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Post subject: Re: (WIP) Laserdisc software image decoder from raw signal Posted: 04 Jan 2014, 05:53 |
Absolute fan |
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Joined: 18 Apr 2012, 18:02 Posts: 1614 Location: United States Has thanked: 71 times Been thanked: 88 times
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Thanks I'm uploading a version made with my current code now (I re-did the TBC and put the comb filter in the same program) My comb filter is good for less sharp footage - it breaks down on something like the Star Wars JSC which is very sharp. It uses heterodyning to get the color information, runs it through a low-pass filter, then adds the out-of-phase bit of that into the combined picture. So it's basically a fancy notch/bypass filter. I don't know when I'll have the time to make a *good* comb filter, but when I recap VE I can send you some unprocessed NTSC output if that'd help you...
_________________ Happycube Labs: Where the past is being re-made, today. [meep!]
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