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High-speed continuous data streaming to PC (analog video)

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I'm playing with the idea to make "my own" analog video capture device for archiving old videotapes because virtually everything on the market for this purpose is garbage except maybe for professional equipment in the multi-thousand-dollar range or some ancient XP-era ATI capture cards that can only be found in landfills. The typical Chinese USB video dongles use the worst quality decoders and don't allow to control any decoder settings or access the raw data.

On the other hand, decent-quality composite/S-video NTSC/PAL decoder chips are ubiquitous and quite cheap, since they are still used in modern TVs and projectors as legacy video inputs, for example a chip like the TI TVP5150AM1 that costs around 6 bucks. There are also a bunch of other inexpensive high-quality decoder chips on the market (mainly from AD and TI). Even the most basic decoder chips have an impressive range of adjustability via an I²C interface and output the digital pixel data over an 8bit or 16bit parallel bus at 27MHz or 13.5MHz, respectively (that's for standard 4:2:2 encoding; some chips support 4:4:4 which only makes sense with a true RGB source).

All I need to do is configure the chip via I²C and stream the digital image data to the PC, which is the challenging part. The maximum data rate is around 30 MByte/s, which should be just within the USB 2.0 capability (including overhead), but I don't know where to begin with the interface controller. I don't need to implement any video capture device standards on the PC side, it's enough to just get the continuous raw pixel data stream via USB into a memory buffer on the PC and write the contents to disk and/or display the video. Is there a general-purpose USB 2.0 interface chip I can use for that, which provides an I²C bus to communicate with the decoder chip and also packages the pixel data into USB frames at the required speed? A microcontroller is maybe the best choice, but which one would be fast enough?

I also thought of misappropriating a cheap logic analyzer for capturing the signal, but it seems like they can only store some number of samples in local memory and then send the memory contents to the PC afterwards, so they can't be used for continuous (i.e. uninterrupted) streaming at this kind of data rates. For a brief moment I was even contemplating whether it's possible to brute-force capture the video signal with a fast ADC and do all the decoding entirely in software - it wouldn't take a lot more data bandwidth than transferring the digitized pixels, but ADC devices made for this speed (basically oscilloscopes) are just never capable of continuous streaming to a high-speed peripherial port (USB, ethernet) or mass storage.



SX3 & FXG2

Take a look at SDRs that have baseband inputs. If you mod the VCR to bring out the raw head signals (buffered using high speed opamps), it would simplify things since you won't have to get one that goes down to near DC, plus you can try all sorts of post processing to get better image quality than what the old analog electronics can achieve.

--- Quote ---The luminance (Y) and color (C) components of the composite video signal are recorded differently. Luminance, which is in effect the black and white picture with all the high resolution components but no color, is frequency modulated on a carrier at around 3.4 MHz. The deviation is about 1 Mhz and the maximum frequency recorded on a VHS tape is a little over 5 Mhz (Beta is slightly different and S versions of Beta and VHS extend some of these to achieve higher bandwidths. The color signal is separated from the composite video and is amplitude modulated on a 629 kHz carrier. This is called the "color under' system.
--- End quote ---

I agree that 99% of the video grabbers on the market are absolute garbage. The dongle just contains a video/audio ADC and streams the raw video/audio data over USB and leaves all the processing to the PC.

There are a couple of exceptions though, that are very rare (no longer manufactured), but with luck can be found on eBay or sinilar sites.

They are the Terratec Grabster AV400 and AV450. I own a handful, all bought for US$ 30...50. Price new was around US$ 120.

So what's special about those two?: they are based on a brilliant Conexant chip set that contains all analog and digital video and audio processing, plus a complete MPEG-2 encoder.
Inputs: Audio L+R, CVBS and S-video.
Output: an MPEG-2 USB stream that can be opened directly with VLC, streamed to your HDD or whatever you like. No drivers or special software needed.

for this purpose I still have a Hauppauge WinTV PVR-350 in an older legacy configuration PC

nothing fancy, just doing what it should


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