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Buffercam - Video Recording Black Box

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Offline buffercam

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Buffercam - Video Recording Black Box
« on: 23 / October / 2009, 21:26:05 »
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I want to create a video recording device that can be mounted on a bicycle or motor vehicle. The device will continually record video, and will automatically preserve a video clip if your vehicle is involved an accident, so you have video evidence of what happened.
This was initially my senior design project from a year ago: we built a prototype with custom hardware, but the results were far from ideal. Now I'm trying to implement this idea with a Canon camera since it can serve as great hardware platform.

I'm looking for feedback as far as the feasibility of this project.

Based on the scripting interface, I'm thinking this could be accomplished by taking a series of videos, say 5 minutes each, and deleting the oldest videos as needed to make room for the new ones.
If this approach were taken, how much time is lost in between stopping a video and starting the next one? (This is probably camera dependent, so I'm just looking for an estimate. 2 seconds? 500ms? 100ms?)

I think the built in camera orientation detection (accelerometer) and image stabilization (gyroscope) may be helpful in detecting vehicle collisions, but at this point I'm trying to see if its feasible to create a circular video buffer like I've described.

Thanks,
David
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Offline fudgey

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Re: Buffercam - Video Recording Black Box
« Reply #1 on: 24 / October / 2009, 03:52:10 »
Quote from: buffercam on 23 / October / 2009, 21:26:05
If this approach were taken, how much time is lost in between stopping a video and starting the next one? (This is probably camera dependent, so I'm just looking for an estimate. 2 seconds? 500ms? 100ms?)
It depends not only on the camera but also on video length and probably the memory card speed and fragmentation too. But I suppose it varies from way less than a second to several seconds.

I would be concerned about the reliability of the setup in case of an actual accident -- if the camera is dropped or even crushed, the video file will likely become corrupt and it may not be trivial to find the video from the SD card afterwards even if it all interesting frames were there. This could be tested of course for instance by removing the battery while recording video (obviously don't do stuff like this on a card that has precious photos on it or with a camera that you can't afford to replace).

Quote from: buffercam on 23 / October / 2009, 21:26:05
I think the built in camera orientation detection (accelerometer) and image stabilization (gyroscope) may be helpful in detecting vehicle collisions, but at this point I'm trying to see if its feasible to create a circular video buffer like I've described.

Don't know about all cameras, but at least mine doesn't have an accelerometer for orientation detection but instead something resembling a mercury switch (obviously one that doesn't have mercury in it... it makes a tiny clicking noises when something moves inside when turning the camera around).

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Offline buffercam

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Re: Buffercam - Video Recording Black Box
« Reply #2 on: 24 / October / 2009, 20:05:05 »
Thanks for your input - you make some good points.

I guess we should be concerned about power loss. In the old system, we were storing individual frames (pictures) so we would lose at most one frame. Here, we could lose the whole video clip prior to the accident. However, we might be able to recover the video if the clusters are allocated sequentially without fragmentation. I think sequential clusters may be likely, if we start with an empty card and deleted the oldest files when we filled it up.

I'm going to take a look at the DCF (Design rule for Camera File system) and FAT32 standards to see if there are any specifications that would help. And I'll definitely need to run some experiments like you suggest.

It's interesting that your camera doesn't have an accelerometer. From your description, it sounds like you have a ball-actuated position sensitive switch. I don't have a CHDK compatible camera at this point, so that may be one of my considerations when I purchase one.
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Offline reyalp

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Re: Buffercam - Video Recording Black Box
« Reply #3 on: 25 / October / 2009, 00:30:28 »
A fairly substantial amount of the video might be buffered in memory.

Generally, these cameras are full of complex mechanical bits. A dedicated solid state cam would seem like a much better choice. There are a lot of these around, although I'm not sure if any record to a circular buffer.
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Offline buffercam

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Re: Buffercam - Video Recording Black Box
« Reply #4 on: 25 / October / 2009, 16:07:56 »
Yeah, that's essentially what I'm looking for. I don't really want a camera with an optical zoom or other fragile parts. But as far as I know, this is the only camera where I can customize the software. There are many dedicated flash video cameras that would be better if there was a programming interface (Flip, Mino, Vado, Zi6, Zi8, iPod Nano, Coby Snapp, MHS-PM1, GC-FM1, etc.).

Let me know if you know of anything.
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Offline fudgey

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Re: Buffercam - Video Recording Black Box
« Reply #5 on: 25 / October / 2009, 16:31:34 »
Quote from: buffercam on 25 / October / 2009, 16:07:56
Let me know if you know of anything.

Cell phones?
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