Software based Time Based Correctors ?

Discussion in 'Amateur Video Production' started by Norris Watkins, Oct 30, 2004.

  1. I have some old VHS tapes, I need to convert to DVDs.
    Are there any Software based TBCs out there.
    If yes, do I need to have the files as AVI
    or can it take MPEG2

    Norris Watkins, Oct 30, 2004
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  2. Norris Watkins

    nappy-iou Guest

    here's alink to a capture card wiht some TBC hardware onboard.

    You might find others with the same.

    You really need to time base correct the stream prior to capturing. A TBC
    uses some memory to store frames and align sync prior to output.

    I think you can pick up a used TBC for fairly cheap now.

    Also. I have a Panasonic AG7750 Editing VHS deck that I have had since
    about 91. Still works like a dream and has a build in TBC, which comes in
    handy sometimes. I rarely capture from VHS. You may want to look for
    something like that.
    nappy-iou, Oct 30, 2004
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  3. Timebase correction is pretty much a hardware function.
    Not really practical to try to do in software as the damage
    has already been done during capture before the software
    ever gets to see it.
    That card that "nappy-iou" recommended looks pretty good.
    It appears to combine TBC functionality with hardware MPEG2
    compression which sounds like exactly what you are seeking.
    Richard Crowley, Oct 30, 2004
  4. Norris Watkins

    david.mccall Guest

    It's not at all inconceivable though. It would have to involve the capture
    application, and I'll bet that it already is.

    All a TBC or Frame Synchronizer does is (most TBCs are frame
    synchronizers as well these days) digitize what ever is coming in,
    find the start of the frame (based on timing and sync pulses), and
    stuff the lines into memory. Then it reads it back from of memory,
    adds new sync (referenced to external sync if desired) and puts out
    the corrected video. All it has to do in a computer is read the lines
    in and put them on a hard drive. The video will come out corrected.

    david.mccall, Oct 30, 2004
  5. That is an oversimplification, and misses the specific function
    of TBCs vs general-purpose video digitizers. Spcifically a
    TBC tracks the exact position of the horizontal sync pulse of
    EACH video line and adjusts the capture window to track the
    timebase errors (which are seen as horizontal skewing in the
    picture). General-purpose video digitizers don't necessarily
    implement this function. although some seem to be better at it
    than most.

    I have heard that there is a plug-in for one of the freeware
    applications that attempts to do line-by-line correction of
    horizontal displacement. (Sort of an after-the-fact timebase
    correction function). But it certainly involves a lot more
    fooling around than using a conventional hardware TBC. And
    of course it can only deal with the video that was captured
    with the non-tracking digitizer hardware, so it doesn't have
    the original sync pulses as a reference point. It has to guess
    from the video whether there is a timebase error for each
    specific line. Given those significant limitations, I doubt that
    it is very effective.
    Richard Crowley, Oct 30, 2004
  6. Remember that there are video capture devices (such as the AverMedia
    device and the Canopus ADVC-300, for example) that specifically
    include TBC *hardware* functionalty. If "the video will come out
    corrected" with any old video capture device as Mr. McCall suggests,
    one would think that there would be no market for these devices.
    Richard Crowley, Oct 30, 2004
  7. Norris Watkins

    david.mccall Guest

    So what did I miss???? I allready said that it locates the beginning
    of each horizontal line, and stash whatever comes after that to memory.
    That's about all a TBC does on the way in. In software you could look
    at the pulse at the end of each line, and make sure that each line was
    exactly the same length by scaleing the line to fit. I'm not at all sure
    hardware TBCs can even do that. The rest of the TBC is pretty much
    of no interest to video capture.

    You could extrapolate line position by anaylizing adjacent lines and
    frames of the video to do the correction, but I don't think TBCs ever
    made it that far. They just base their capture on the incoming sync,
    and base their output on either external sync source, or just on internal
    sync generator. TBCs usually have a proc amp and comb filters built in,
    but both could also be done in software.

    david.mccall, Oct 30, 2004
  8. Norris Watkins

    david.mccall Guest

    I don't know that there is much of a market for TBCs in non-linear suites.
    I'm not suggesting that all capture devices are equal, or can all manage
    to correct incoming video no matter how wide the time variations are.

    david.mccall, Oct 30, 2004
  9. Norris Watkins

    Larry J. Guest

    Waiving the right to remain silent, "david.mccall"
    Hardware TBCs generally do that and more. Most now contain
    "velocity" error correction, frame synchroniation, and a full proc

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    Larry J., Oct 30, 2004
  10. Norris Watkins

    G L Guest

    Here's an inexpensive harware TBC
    for $200, AVT-8710:

    It works well for VHS/S-VHS/Beta.
    It's in other countries, but has other
    brand names (search with the specs).

    Maybe a software thing could be
    made, but it would be guessing
    all the time, with weird side effects.
    G L, Oct 31, 2004
  11. Norris Watkins

    Mike T Guest

    His descripting is functionally accurate, as this is what a TBC is. A video
    digitizer is also a TBC.

    The basic TBC function is accomplished by digitizing the video signal and
    storing it in memory. What separates the MEN from the boys is how well the
    sync signals are extracted from the incoming analog video stream and how
    well the "write" clock tracks the video incoming frequency rate. So for a
    VHS type of player, the clock generator must correct for the head-switch
    error so that there is no picture hook or bending at the top of the screen.

    Thus, you have two big problems, First, the sync signals are usually
    distorted and compressed by the tape recording, especially with multiple
    generations of analog recording and, Second, you need to be able to store a
    complete frame of the video signal in memory in exactly one frame of memory,
    so as the playback frequency of the video signal drifts over time, the
    "write" clock must be able to very accurately measure the incoming video
    rate in the presence of noise, sync compression and tape drop-outs, head
    switch tension errors and I believe the current "phase of the moon" was also

    Over about 20 years of designing TBC's I used many different sync extraction
    methods and several different clock generators to try to find the best,
    never did.

    For the First digital TBC designed in 1972 I used a PLL clock design to lock
    to incoming horizontal sync and incoming color burst signal as it was a
    "composite" video world back then, I am very glad it is now gone.

    Mike Tallent
    Mike T, Nov 2, 2004
  12. I remember daily battles with a Phillips/Norelco
    3-plumbicon color camera with a horizontal sync
    circuit that had a mind of its own. Half the time it
    had no concept of "genlock" and would wander
    around like a feather in the breeze.
    Richard Crowley, Nov 2, 2004
  13. Norris Watkins

    david.mccall Guest

    A good piece. Thank you. and thank you for being a part of that
    first TBC. How many lines could it do? What company?

    Looking back at it now, I'll bet you wished you had microprocessors
    to analyze the signal, instead of just PLLs. On advantage to "capture"
    alone is that you don't have to put the video back out in real time, you
    just have to get it onto a hard drive. With current microprocessor
    speeds, you should have a lot of advantages in terms of line to line,
    field to fields, and even frame to frame comparisons, to get all of those
    pixels lined up just right.

    I'm not saying that they are doing a good job of it, I really don't know,
    but it should be practical to capture most anything directly into the
    computer without an external TBC. I have an old Matrox Digisuite
    and it seems to handle everything I've thrown at it so far, but I really
    haven't had to test it much. I realize that a lot of people are using
    capture cards that are well under $5000, so I wouldn't be surprised
    if their performance was somewhat different. However, there has
    been a lot of time for improvement since this thing was designed.
    A 300 mhz computer was a cooker back then.

    david.mccall, Nov 2, 2004
  14. Norris Watkins

    Mike T Guest

    The first digital TBC was introduced by Consolidated Video Systems (CVS) at
    NAB 1973, it was 8 bits at 3X color or 10.7 MHz and had a correction range
    of 3 horizontal lines, using 1024 BIT dynamic shift registers as the largest
    RAM chip was 256 BITS and need several support chips per RAM. UGH! I was a
    founder of the company and project manager on the TBC and designed the
    analog parts with another designing the A/D converter and a third doing the
    digital "stuff", guess we helped to put the "silicon" in Silicon Valley.
    Sure was a lot of fun in those days in N. Cal.

    After CVS, I did ADDA Corp and ALTA Group "stuff"

    Here are a few of the patents on this stuff--

    In case you want to know more ;-)
    I don't think today the computers are fast enough to do much analysis on the
    video signal in real time, and to store the video into memory you STILL have
    to know WHERE the video line starts and if you do that correctly the TBC
    function is complete.

    To store the complete sync pulse into memory in order to analyze it would be
    a waste of dynamic range and you still have to "DC" restore the sync pulse
    to set it at the proper video level into the A/D converter and if you can do
    a proper DC restoration on the incoming video, then you also "know" where
    the video line starts so you would also know how to perform the complete TBC

    So software is not a solution for this "hardware" problem, at least not yet

    Mike T
    Mike T, Nov 2, 2004
  15. Norris Watkins

    Seattle Eric Guest

    I used to have a dual ADDA TBC. That thing was so coooooool.

    Seattle Eric, Nov 3, 2004
  16. Norris Watkins

    david.mccall Guest

    I think a 16 line CVS may have been my first, and I owned
    a Pyxis for many years.

    david.mccall, Nov 3, 2004
  17. Norris Watkins

    Mike T Guest

    The ADDA AC-20 was the first dual channel TBC with special video effects, it
    seemed like a good idea with all the A-B roll editing going on at that time.

    Got spare parts and manuals for most of these products if anyone needs one
    repaired today ;-)

    Mike Tallent
    Mike T, Nov 3, 2004
  18. Norris Watkins

    Steve Guidry Guest

    I'm still using a Pyxis, a Pyxis-E in my dub rooms, and my Centaurus is the
    main still store in my production truck.

    Steve Guidry, Nov 3, 2004
  19. Norris Watkins

    david.mccall Guest

    I donated my Pyxis E to the local access channel.
    It sat on the shelf for a year or so then tried to use it.
    They plugged it in and it smoked. So they never got to use it.

    david.mccall, Nov 3, 2004
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