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Old Aug 24, 2006, 11:36 AM   #1
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I have noticed many of the still camaras coming out have either mpeg 4 video or motion jpeg.* Which technolgy is better?* Do they both take up same amount of space on a card?
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Old Aug 26, 2006, 4:45 AM   #2
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Motion JPEG (MJPEG) is an older video format which was developed and included in the Apple QuickTime format. It uses the principle of a "flipping picture book": each frame has the stickman's arms and legs in a slightly different position. When you flip the pages quickly, it appears the stickman is walking. MJPEG is supposed to have excellent frame-by-frame video quality, because of the simple fact that the image of every frame is saved. The problem is, the video filesize is huge - 1 GB can only store about 5 or 6 minutes of video. To overcome this problem, many camera manufacturers reduces the video quality (eg. keeping the screen resolution low (eg. 160 X 120 or 320 X 240 pixels); keeping the "frames per second" (framerate) low (eg. 12- 15 fps); keeping the video bitrate low) in order to squeeze in more minutes of video, but they rarely get above 10-15 minutes per GB. A video with lower quality settings, despite good frame-by-frame quality, is still a low quality video overall.

The advantage of MPEG4 movies is small filesize for decent to good video quality. This modern video format uses a lot of data compression (which requires a lot of computer processing power from the computer chip inside the camera) to achieve small filesize. Unlike MJPEG and older video formats, where the information of every single frame of the movie is stored, MPEG4 only store "keyframes" when there are major changes in the scenes. It uses extrapolation to build the frames in between - for example, a scene of someone walking by: the face is relatively unchanged so the video does not have to store repetative information on the face; the arms and legs move as he walks, so the video projects these movement rather than storing the actual images of the moving limbs. Depending on the quality settings made by the camera manufacturers, 1 GB of memory may contain up to 40 minutes of decent to good quality MPEG4 videos at good screen resolution (eg. 640 X 480 pixels).

Currently not many digital cameras use MPEG4 format - the only ones I know are Sanyo, Casio, Olympus, Aiptek/ Mustek and other non-brandname hybrid cameras. Many users are not familiar with the MPEG4 video formats, and they don't know how to edit and convert them, or even how to watch them. MPEG4 is actually a family of different video formats, but the most popular format used again seems to be the Apple QuickTime (MOV). Most manufacturers include a copy of Apple QuickTime player to play the movie on Windows PC, and there may be simple video conversion (+/- editor) software that you can use to convert the camera's video to popular video formats like DVD (for burning). So look through all the installation disks of the camera.

There is a lot of confusion about the video file extension and the true video format - video with MJPEG format may have extensions like MOV (as in QuickTime) or AVI. MPEG4 format may have extensions like AVI, MP4 or MOV. Therefore, you cannot really tell which format the camera use just by looking at the video file extension. The only sure way is to read the user manual (many can be downloaded from manufacturer's website, you can take a look before you buy the camera) and see how many minutes of video per GB memory it uses - if 1 GB only holds 15 min of less (at 320X240 screen resolution), it most likely uses MJPEG format. This is just a rule of thumb though.



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Old Aug 26, 2006, 1:30 PM   #3
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blindsite,Thank you* so much for you detailed explanation.* I dfinitely have a good understanding no of how the different video formats work.* Thanks for making it simple enough for me to understand and for taking the time
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