Archos AV 500 + Bullet Cam

Discussion in 'Video Cameras' started by trezaei, Jul 29, 2006.

  1. trezaei

    trezaei Guest

    Hi folks. I was hoping your video expertise could point me in the right
    direction.

    I own an Archos AV500 DVR and an unmarked (Sony CCD) Bullet cam.

    When I set the bit rate on my Archos to record at anything over 500 K/s
    after it records about 100MB of video it somehow corrupts the file. If
    I set it to 500k/s it seems I can record as much as I want.

    1) I was wondering, is it possible that somehow the bit rate provided
    by the camera just doesn't match right with the recorder and it ends up
    corrupting the file?

    2) Or maybe at high bit-rate, the camera has simply too much info to
    process and the Archos just can't write to the disk fast enough and it
    get screwed up?

    3) If 2 is the case is there some sort of buffer device I can put in
    between the two?

    4) I have been recording while on my motorcycle. Fast acceleration
    (0-60 in 2.9 sec). When things are moving faster is it possible the
    video size is larger? Maybe because there is more info to record? Or
    maybe the disk in the Archos just can't handle the Accel and the high
    bit-rate at the same time and it craps out?

    Anyway, any suggestions would be appreciated.

    Thanks
     
    trezaei, Jul 29, 2006
    #1
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  2. trezaei

    G Hardy Guest

    I'm pretty sure that the bullet cam will be providing an analogue signal -
    correct me if I'm wrong. As such, the bullet cam itself is not part of your
    problem, because it is always providing the same amount of picture
    information.

    The USB connection shown in
    http://www.archos.com/img/av_500/download/AV500_cam.png provides power to
    the bullet cam - not data from the bullet cam. Is your setup similar?

    500kbit/sec is a very low bitrate - even lower than VCD. Even at MPEG-1
    half-D1 (352x288) you're going to struggle getting a decent encode from
    that - especially of "high action" scenes like the acceleration. I'm not
    clued up enough on MPEG-4 to know what sort of quality you'll get at that
    bitrate from 30fps, 640x480

    It's possible you're talking about 500Kbyte/sec, which is more appropriate
    for what you're trying to record (it equates to 4mbit/sec).

    Either way, I expect that the Gs you're pulling on acceleration is outside
    the operating parameters of the inbuilt hard drive, and when you get too
    high a bitrate, the buffer fills when the drive heads are unable to write.
    If this is the case, you should be able to record at the higher bitrates
    when not on your bike. If you can't even do that, then the acceleration Gs
    are not the problem. Note that if it is the problem, you could well be
    damaging your unit by subjecting it to such extremes.
     
    G Hardy, Jul 29, 2006
    #2
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  3. trezaei

    trezaei Guest

    I'm using a different camera powered by a batter pack.
    I am recording at 500 k/s bit-rate and you're correct it looks
    terrible.
    I am going to try and leave the archos on the bike sitting still at
    high bit-rate (2500) and see if it has any problems. I am thinking, as
    an alternative maybe mounting the archos unit so that the acceleration
    is on the same axis as the rotation, that might help a bit.

    Is there a way to increase the buffer by adding another device in
    between?

    T
     
    trezaei, Jul 29, 2006
    #3
  4. trezaei

    G Hardy Guest

    If I were insane enough to put my hardware (and myself) through that sort of
    torment, I'd be considering a fully solid state setup. Depends how much
    recording time you need. I can't think of any solution that is pre-built,
    though - you'd probably need to hack something together yourself. Is there
    such a thing as a pocket PC that boots to XP or similar from ROM, and has
    two USB2 ports? If so, you could take the feed from the camera and send it
    through a USB MPEG-2 encoder, and the resulting stream is stored by the PC
    on a compactflash card or similar.

    I think that you'll do more damage to the hard drive in the Archos if the G
    force is on the axis of rotation (assuming, of course, that that's the
    reason for the problem). If it's on the X or Z axis, the drive heads will be
    pinned against the inner or outer boundaries of their sweep. If it's on the
    Y axis, the heads may well be forced into the disc platters as they are
    spinning.
     
    G Hardy, Jul 30, 2006
    #4
  5. trezaei

    G Hardy Guest

    Sorry for replying to my own post, but
    http://www.informationweek.com/windows/showArticle.jhtml?articleID=177102101&pgno=4
    describes how you can boot a PC from a USB key. So all you need to do is
    pull the hard drive from a mini laptop such as a Tosh Libretto, boot it
    using a USB key, and capture the analogue using a hardware encoder such as
    this one:
    http://svp.co.uk/products-solo.php?pid=492
    onto a separate solid state drive.

    There are possibly several "pocket PC" solutions that do not use moving
    parts, but I'm not up-to-date when it comes to mobile computing.
     
    G Hardy, Jul 30, 2006
    #5
  6. trezaei

    trezaei Guest

    Okay so here's an update.
    The problem is probably the acceleration.
    I left the archos sitting on the bike for 4 hours today. It created
    around 6GB of flawless video.
    So that sucks. Because it means I can't go fast on the bike with the
    archos running.

    The length of video I am going after is about 1-2 hours. Which
    translates to about 4GB max.

    I could get a CF card that big, which I actually have, but those things
    are pretty slow and I am not sure they can handle the write speed
    required.

    The V-Stream device you pointed out sounds neat but I still don't
    understand how you can save the file onto a solid state device with no
    PC ..

    How would this setup work exactly?

    For now I am going to try mounting the Archos with spin axis facing
    forward despite your warning. If I can't use it for what I need I might
    as well test its limits :)

    T
     
    trezaei, Jul 30, 2006
    #6
  7. trezaei

    G Hardy Guest

    Wohoo - it's not often I get something (probably) right ;o)

    No, it just means you can't accelerate the way you do - it's the Gs that are
    the problem, not the speed.

    MPEG-4 should compress much more than that, I'm sure. That's about the size
    you can expect for DVD-quality MPEG-2...

    Sure they can - it's the USB that will be the bottleneck. I have CF cards
    that write at 6MB/sec (48,000kbit/sec)

    You _would_ need a PC - the CF card and reader combo (or any other USB key
    setup) is a "mass storage device" which needs an operating system to handle
    the file system.

    You have the bullet cam -> video streamer (composite or s-vid link)
    video streamer -> pocket PC (USB link)
    Pocket PC -> solid state storage (e.g. CF card attached to another USB)

    The "pocket PC" would probably have to be a self-build, as I'm not aware of
    any that will boot from solid-state devices. It would also need to get power
    from somewhere - do bikes have power outlets?

    Good luck - let us know how you get on.
     
    G Hardy, Jul 30, 2006
    #7
  8. trezaei

    trezaei Guest

    Correction, I can't accelerate as fast which is really the fun of a
    motorcycle.
    www.chasecam.com already has what you're proposing, I went with the
    Archos UNIT not anticipating a problem with the disk since Archos
    claims this is one of the applications they sell the product for.

    I was thinking of a possible spring loaded force dampener, that would
    allow the Archos unit to move a few inches when a force is acting on
    it, That might help a bit. So I built this rig last night that I am
    gonna try out today. I have a pretty good feeling about it.

    Although I have to say that Acceleration isn't really that important
    when it comes to making a good movie on a bike. Its really capturing
    the turns and the lean angle of the bike + splitting lanes and what
    not. So I guess when the camera is running I have to make sure I keep
    it under wraps.

    I get from 0-60 mph in 2.9 sec. give that 1 mph = 0.44704 meters /
    second

    That's 0 - to 27 m/s^2 in 2.9 sec which if I was accelerating Linearly
    is approximately 1Gs. Give or take.

    Anyway, how much acceleration would you assume your average Hard Drive
    can withstand without having issues?
     
    trezaei, Jul 30, 2006
    #8
  9. Actually, shock tolerance (measured in Gs) is one of the standard
    quoted specs of a hard drive. Find out what's in there, and try the
    manufacturer's site.
     
    Laurence Payne, Jul 30, 2006
    #9
  10. trezaei

    trezaei Guest

    Shock tolerance is one thing but keeping the same acceleration going
    for 3 full seconds is another. I will check but I am assuming it will
    be on the order of 10Gs.
     
    trezaei, Jul 30, 2006
    #10
  11. trezaei

    trezaei Guest

    I checked it and here is the number, pretty incredible really:

    Vibration and Shock:
    Operating Vibration 9.8 m/s2 (1.0G), 5 - 500 Hz
    Operating Shock 325g
    Non-Operating Shock 850g

    Link: http://tinyurl.com/flmsn
     
    trezaei, Jul 30, 2006
    #11
  12. It's measuring shock in grams? How does that work?
     
    Laurence Payne, Jul 30, 2006
    #12
  13. trezaei

    trezaei Guest

    Lol, you might be right but I thought it was measuring it in gs. 1g
    being 9.81 m/s^2 :)
     
    trezaei, Jul 31, 2006
    #13
  14. trezaei

    G Hardy Guest

    Is there an acceleration curve for your bike anywhere online? There's no
    reason that a 1G load should hamper the hard drive (it's being subjected to
    that load all the time anyway).

    All the figures I can find point to short shocks (milliseconds) which equate
    to being dropped onto a hard surface, but for those durations it's in the
    hundreds of Gs (thousands if the drive is not operating). Doesn't help you,
    though, as you're giving it less shock over a longer duration.
     
    G Hardy, Jul 31, 2006
    #14
  15. trezaei

    Sparks Guest

    You may want to try just rotating the unit, keeping the back of it pointing
    up or down.
    The hard disk heads are like a record player, so if you had them pointing
    backwards when you accelerate, not sideways, it might just work :)

    Having the back or front of the unit facing forwards is just asking for the
    heads to grind into the platters!

    Sparks...
     
    Sparks, Aug 3, 2006
    #15
  16. trezaei

    Andy Champ Guest

    He's probably traction limited up to that speed, so it'll be near enough
    a flat curve.

    However, that's 1g horizontal *in addition* to the normal 1g vertical,
    so it's running at 1.4 or so. I'm surprised that causes a problem, I'd
    have thought vibration more likely - so trez, stick the Archos inside
    your shirt pocket. Probably the smoothest ride. And yes, try different
    angles!

    Andy
     
    Andy Champ, Aug 6, 2006
    #16
  17. Yes, I'd wondered too if we were chasing the wrong problem.
     
    Laurence Payne, Aug 7, 2006
    #17
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