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Old Jul 6, 2006, 1:37 AM   #1
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Trying to decide on a camcorder/still - (Hybrid) camera. Comparing the Sanyo XACTI line with something like the Sony M! or M2. What is MPEG 2 good for versus MPEG 4 . Which is better or what specific uses are they aimed at. Can anyone give a good explaination of the comparison? MPEG-2 vs. MPEG-4
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Old Jul 6, 2006, 12:15 PM   #2
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MPEG2 and MPEG4 are 2 different compression schemes to compress digital video into smaller size, while making some compromises in image quality.

MPEG2 is older than MPEG4, and is used in DVD's.

MPEG4 is newer, and will be used in the upcoming HD-DVD and Blu-Ray formats. Because it is newer, it is more efficient at compressing data than MPEG2.

Some caveats:

1. Both formats can deliver great picture quality, as long as the 'bitrate' is sufficient. Meaning that a 60 second 640 x 480 video clip compressed to 10 MB is going to look bad no matter which compression scheme is used, and a 100 MB sized clip should look great in either format. DVD's look great because there is tons of storage space available.

The advantage to MPEG4 is that you should be able to save storage space at a given level of quality compared to MPEG2.

Typically, a camera using MPEG2 (or MPEG1 or MJPEG) will use 1 to 2 MB per second of video. A camera using MPEG4 will typicall use somewhere around 500KB to 1 MB per second of video. (these are just rough guidelines.) I believe the DV format in consumer digital camcorders uses about 2 MB per second of recorded video.

2. MPEG4 is theoretically superior, but any particular camera may do a better or worse job of MPEG4 encoding. For example, some of the early Samsung models with MPEG4 used either poor encoder or insufficient bitrate, and seemed to give poor results (I imagine current models are improved.)

Because of these 2 factors, it is important to see actual samples from the cameras you are considering, if shooting video is important to you. This site and DCResource.com both include sample videos in all their reviews.

Finally, make sure you consider other factors outside of video compression method or even quality. Resolution and frame rate are obviously important. Audio quality varies widely among cameras. Some allow you to use zoom while shooting, some don't. And many now have image stabilization, which can make video clips much less jerky. Finally, for extensive video shooting the storage card format of the camera can be important, since some cards are more expensive than others.

I have been looking around for a compact, inexpensive digicam that will shoot VGA 30FPS video. I used to care a lot more about looking for a MPEG4 camera, but realize that compression scheme is just 1 factor among many. Now that you can buy 4GB SD cards for under $100, getting maximum compression is not as important as it used to be.
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Old Jul 6, 2006, 2:12 PM   #3
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madmaxmedia wrote:
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1. Both formats can deliver great picture quality, as long as the 'bitrate' is sufficient. Meaning that a 60 second 640 x 480 video clip compressed to 10 MB is going to look bad no matter which compression scheme is used...
Wrong, in 2-pass compressed "DivX" movies splitted to two CD-ROM audio track (AC3=DD5.1) generally takes about 100MB which leaves 600MB for video... and 60 minutes of video fits to that quite well while retaining near DVD quality.
With good codec MPEG4 is way superior giving at least 2x efficiency with same quality.

So MPEG2 is worse than MPEG4 in every aspect, maybe except in processing power requirements.
But because of limited supply of battery power compression is always done using hardware encoder/ASIC in this kind devices so doing good MPEG4 compression shouldn't be prevented by lack of processing power in general purpose ICs. (dedicated ASICs are huge amount more efficient in that specific job than general purpose processors, for example remember jump in quality of game graphics when PCs got 3D-(graphic)cards)


Commonly used Motion JPEG (MJPEG) is intraframe compression which encodes every frame separately while others use interframe compression with associated motion compensation/prediction which saves only changing parts of image between keyframes increasing efficiency considerably so this is least efficient of these video compressions.
Reason why you don't find files with MJPEG ending is that video stream (with audio stream) is inside container file, like AVI or MOV (Quicktime).



PS. DV videos take about 35Mbps which is ~4MBps. Also DV is intraframe compression making it good for editing.
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Old Jul 6, 2006, 3:18 PM   #4
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My main concern is to get a camera and editing software for the MPEG format that will be preferrred over the other (MPEG 2 or 4) . As an example TV news people in the feild, will their cameras use 2 or 4? What about TV industry and consumer camcorders in general. We all know tape is going away. What will be the eventual commonly used standard???
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Old Jul 6, 2006, 7:50 PM   #5
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Oops, thanks for the corrections. I was making an example off the top of my head, I should have said say 3 MB!

Most of the MPEG4-based digicams seem to use bitrates around 500 KB or so per second (audio and video) with some compression artifacts (although most digicams show video compression artifacts.) I was just checking out the Sanyo Xacti C6 review here, and it has great quality at very economical bitrates. Hmmm...

I completely agree that MPEG4 is superior to MPEG2, just wanted to qualify it a bit so the OP wasn't expecting miracles. It still pays to check out sample clips.

Some of the best quality clips I have seen are from the newer Canons, which use MJPEG (albeit they take up much more space as you say.) Each person has to decide which camera is best for them.

Can you clarify on this?

"Reason why you don't find files with MJPEG ending is that video stream (with audio stream) is inside container file, like AVI or MOV (Quicktime)."

Also, since MJPEG is intraframe, does that make it good for editing as well? (using home stuff like iMovie, etc.) I am guess for home stuff (where you don't need exact/precise cuts), it's not that big of a deal.

Thanks
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