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Old Oct 10, 2007, 3:31 AM   #1
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Hi guys, new to this forums and have my very 1st question. Any informative input is greatly appreciated.

Okay, as most of you guys know (I think?), when recording a video/movie on a camcorder their is usually 2 modes to choose from, SP (standard play) and LP (long play). I understand that using LP on a miniDV tape their is compatibility issues with viewing on other cams and possibly on the one that recorded it, maybe less quality, and less shelf life for the recorded movie on the tape, for an additional 30min extra of recording.

Now my question is, does what I stated above apply to digital video recordings on a camera as well? (movie mode) Personally I don't think the data is influenced in the same effect.

The reason I'm asking is that I plan to purcahse the Canon Powershot SD870IS and I noticed they have the LP recording feature (640 x 480 (30 fps/30 fps LP) for the sd870is and sd950is, something not featured on the remaining powershot lineup.

Just wondering because I plan to do recording on it (yes pictures too), and wouldn't mind using the full potential of the recording limit. On normal 640x480-30fps its about 30min of recording using up 4gb of space (max record limit), whereas if in LP mode it would record upto 60min for that same amount of space. Basically the best of both worlds, being able to record an hour of a good quality recording (on a camera) within the recording size cap (4gb) = AWESOME!!!!

Anyhow thanks for reading and hope to hear from you soon.


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Old Oct 10, 2007, 9:11 AM   #2
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Sorry to have to tell you this, but there's no such thing as a free lunch. When you double the compression using the same algorithm, you degrade the image quality. The Canon uses a kind of compression called Motion JPEG for its movies. This is not good if you care about the size of your movie files. Basically, Motion JPEG compresses each frame using JPEG, and stuffs the results into an AVI wrapper. Much better compression is any variant of MPEG. The difference is this -- MPEG compresses across frames, while JPEG is within-frame compression only. The most similar thing to most frames in a movie is the frame right before or after it. If you take the similarlity of frames into account, you can get a lot better compression usually. The rule of thumb is that MPEG typically can compress ten times as much whilepreserving the same video quality as JPEG.

But there's again no free lunch. The downsides of MPEG compression are twofold. First, if you edit MPEG files, they fall apart quickly. The reason for that is because the compression is based on groups of frames. If you "cut" the file in the middle of a group, it tends to get very low quality at the cut. The second thing, and for the same reason, is if a scene changes quickly. You have probably seen digital television images become filled with blocks at some transition for a while. This is a common visual artifact of MPEG when scenes change rapidly. Both of these effects are avoided (or, more precisely, minimized) in Motion JPEG files -- but at the cost of massively larger file size. FWIW.


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Old Oct 10, 2007, 12:56 PM   #3
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Thanks for the reply, one can dream of a free lunch, or possibly apply for a reduced or free lunch program which in no doubt is not a solution for the issue at hand :-)

What you have stated I already knew, I guess I was trying to deny myself until I heard it from someone else. I have come to admit it, and well, it sucks :sad:

CANON IF YOU READ THIS PLEASE INCREASE CAP TO I DUNNO 8GB, why is their a cap in the 1st place, on canons website it states the cameras can use quote from canon's site - "Secure Digital High Capacity currently supports capacities up to 32 GB". (which I don't know if there is one), why not just leave it at that, but again I'm lying to myself, their could be software/hardware issues atm that prevents media to be recorded above 4gb or maybe they just haven't looked into making it that way and actually using this cap to benefit "improve" future products to make them seem better. lol yes im harsh.

Again thanks for replying.
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Old Oct 11, 2007, 6:43 AM   #4
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FAT32 (the file system used for card sizes > 2GB by camera manufacturers) has a file size limitation of 4GB.

http://en.wikipedia.org/wiki/File_Al...on_Table#FAT32

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Old Oct 11, 2007, 10:37 AM   #5
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JimC wrote:
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FAT32 (the file system used for card sizes > 2GB by camera manufacturers) has a file size limitation of 4GB.

http://en.wikipedia.org/wiki/File_Al...on_Table#FAT32
Just to belabor the obvious, that is the maximum size for a SINGLE file, which would not be a problem in the vast majority of cases. If memory serves (and this may have changed since the last time I worked with the format) AVI files are limited to 2GB per file.


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