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Old Nov 15, 2005, 6:51 PM   #1
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Hi

I wonder of you S2 owners could enlighten me about one point of the Specification.

Both on this site and the Canon web site it says maximum movie size 1GB and 1 Hr, implying that it is possible to get a 1 Hr movie out of the camera.

I fail to see how this is possible.

The data rate for the 640x480 30FS mode is ca 2M which gives about 8 mins of movie for 1 GB.

Even with the lower resolution setting of 320x240 30FS a 1 Hr movie does not seem remotely possible.

Since I am considering this as a possible choice for my new camera and I am particularly inerested in the movie capability I really would appreciate comments on this. I thought a movie of this length on a digicam would only be possible with an MPEG4 camera and this is not one.


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Old Nov 15, 2005, 7:40 PM   #2
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Gidday

At 320 X 240 15fps you will get approx 30min on 1gig

Cheers Dom
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Old Nov 16, 2005, 3:38 AM   #3
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Gidday ( coming over to Oz again in Jan so must practice my Giddays )

Thanks for info.

I came to my earlier conclusion as I did not appreciate that 320x240 & 15FS was an option. From the review on this site the 3 options appeared to be

640x320 @30/15FS & 320x240 & 30FS.

I am now a little puzzled again.

From several sample movies I have seen, all taken at 640x320 @30FS, the data rate is ca 2M so a 1G memory would store ca 8 mins of movie.

Using 15FS rather than 30FS (1/2 the number of frames ) should double this to ca 16 mins.

Should not then reducing the resolution from 640x480 to 320x240 then increase this further by another factor of 4 ( 1/4 timethe number of pixels per frame ). This would then give the alleged storage of ca 1 Hr for 1G memory.

Is there something wrong with my logic ?


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Old Nov 16, 2005, 9:05 AM   #4
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Gidday again mate

Your logic sounds very good but on the S2 screen it shows the different vid size options and time they will run -i'm sure someone could explain the reason behind it.

The longest vid in one hit i took was about 5mins - that was just to test it out and it seemed like a long time.Have'nt used it much at all but seems like a handy thing to have for a one-off event if you have'nt got a video cam in your back pocket.

Cheers Dom
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Old Nov 16, 2005, 9:45 AM   #5
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Thanks again.

I probably would not use the 320x240 15FS combination butI was interested to see howCanon justified their 1 Hr statement.

It will be interesting to see comments from other user''s, who make more use of their movie facility.

I guess the 640x480 15FS might be the compromise I would use to extend the movie length for low speed movies.

We passed through Geelong on a previous visit to Oz after the spectacular drive along the Great Ocean Road. You have a nice country down there.
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Old Nov 16, 2005, 10:44 AM   #6
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Hello,

Your calculations / estimatesare slightly off. Dropping the # of frames per second (fps) from 30 to 15 does not exactly double the maximum movie length (MML for short). Neither does doubling the memory size (say from 512MB to 1GB). And switching from 640 mode to 320 mode definately does not quadruple the MML. There are longwinded explanations for this but here are short answers. 30->15 will not double MML because you have less frames per second (fps) thus less compression capability. Imagine if the camera could shoot say 100 fps. Anyrandom frame would be so similar to the previous and next frames that the compression potential would be much greater. Doubling the memory size has more overhead to manage the memory so you dont get exactly double but close to it. Dropping from 640 to 320 for an uncompressed BMP file would lessen the storage requirement to 1/4 of the original. However, when dealing with movies on this camera (and JPGs for that matter), it is more like 1/3 or 2/5. This is probably because as you have less total # of pixels per frame, there is less possibility for compression because neighboring pixels will probably be more different than each other in a smaller image. Again, imagine an image of say size 5000x3750 (about 20MP). With that many pixels, neighboring pixels will be very similar to each other and thus you can get much higher compression ratios easily. Now imagine the same picture but only 320x240 size. All that same scenery has to be "squeezed" into only 320x240 pixels so neighboring pixels will be much more different than in the 5000x3750 example. So it looks like with the corrected calculations, MML is more like 40 minutes for average action footage (with motion) using 1GB memory card. Perhaps Canon anticipated best case for compression and limited it to 1 hour based on that. If you shot a movie with the lens cap on it may go for 1 hour however that is not a real movie.If you shoot a movie that has many scenes that compress well, that 40 min could easily stretch into 60 min. For example, if you shoot a racing event on a tripod and there is only brief amounts of motion once per lap that you are shooting. By the way, if you think 2MB/sec is excessive data rate for 640x480 at 30fps think again. If the camera were to store thirty 640x480 uncompressed BMP type images each second, that would be over 26MB/sec of storage requirement. Because a camera has very limited horsepower, it cannot optimally compress a movie real time. If you postprocess your movies using some very high quality movie software, you can get that 2MB/sec down to about 0.2MB/sec without much loss of quality. Windows XP movie maker can compress 10:1 but the result will be 320x240 and reduced quality andyou need a very fast computer for that software. Hope this helps. If you are interested in a good tele lens for the Canon S2, I can give you some good advice on that too so email me. About 1.5x mag with 3x zoom capability and excellent image quality. Have fun.
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Old Nov 16, 2005, 11:26 AM   #7
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I was under the impression that the video on this camera was NOT compressed...
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Old Nov 16, 2005, 12:20 PM   #8
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Hello,

The Canon S2 movies ARE compressed if you compare them to the equivalent 640x480 30fps of uncompressed "BMP" type images. For uncompressed 24 bit color images at640x480 30 fps, the storage requirement would be about 26MB/sec so at 2MB/sec moviedatarate, that is already compressed about 13:1. Good software can compress that another 10:1 without much loss of quality. If the S2 had no compression at all, this 26MB/sec datarate described above would limit 1GB movies to about 40 seconds. Because of the 13:1 compression in the camera, the 40 seconds becomesabout 520 seconds which isabout 8 minutes. This high datarate is why you dont see full resolution movies on digicams. Imagine if the S2 allowed 5MP movies instead of 0.3MP (640x480) VGA movies. That would be about 17 times more uncompressed storage reqirement so only about 2 seconds to fill a 1GB memory card! Those uncompressed images would be 15MB each and in 2 seconds you would capture 60 of them (at 30 fps) so 60*15MB = 900MB = almost a full 1GB memory card! You should now see how compression is absolutely critical to digital movies otherwise the very high datarates would not allow any significant length of capture time. You should feel lucky that 640x480 is even an option for movies. Hope this helps.
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Old Nov 16, 2005, 12:57 PM   #9
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herbsbuddy:

Thanks for that detailed explanation of memory requirements - very kind of you to take the time.

I was using a very simplistic approach in my assessment and not taking into account the non-linear effects of compression.

I am familiar with the sizes of uncompressed files as I had tried converting movie files with "RAD Video Tools", which seems to convert almost anything to AVI and gives quite a few options in terms of codec to be applied, e.g. DivX and XviD, as well as an Uncompressed option. As you say, the uncompressed files are huge.

I should have twigged that my logic for memory use was wrong since, when I had used Windows Media Encoder and tried various conversion options. I had seen that 640x480 files are not 4 time the size of 320x240 files but had forgotten this.

The result of all this is therefore that the 1 Hr movie is not really on, even with worst quality. I guess that ca 15 secs would be maximum with the 640x480 15FS option.

Many of the posted sample movies are with 640x480 30FS but the one on this site for the Canon A70 has 640x480 15FS, is of moving cars and looks reasonably smooth so I guess this is a usable mode.
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Old Nov 16, 2005, 9:17 PM   #10
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Hi,

I would recommend shooting in the highest quality mode (640x480 @ 30 fps) then using software to shrink down the filesize for email purposes. That is, you can keep the original on your hard disk and use a 1GB jumpdrive to load on a local friends or relatives computer (winzip the file first if it doesn't quite fit) but for emailing, use Windows XP movie maker or other movie software to create a much smaller format that is emailable. I would recommend about 2MB per minute max for movies which works out to about 256Kb/sec or 32KB/sec (b=bits, B=Bytes) since the camera maxes out at about 8 min of movie in highest quality movie mode and AOL has 16MB upload/download limit that works out nice. Since you might not use AOL but many other still do (including me), you need to accommodate them and don't assume everyone has high speed capability. If you think you will be shooting lots of movies, then get a 2GB memory card so that even if you max out a 1GB movie, you still have plenty of memory for other shorter movies + lotsa still images. I think the Canon S2 allows 2GB memory cards although I have not tested it personally. Have fun!
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