Understanding file sizes

[willydeluxe]

I am amazed at the high quality of the finished video: it's almost as if VS9 is rendering only the transitioned areas - but that's not right, is it?

I'd like to understand what happens to a clip after editing and rendering to make it increase so much in size. Example: a 19 minute, 101Mb avi, when edited to 4 minutes with a crossfade between each clip (about 12, can't recall) rendered as Mpeg2 is 155Mb in size: how come?

I rendered another project first as Mpeg2 - 305Mb, then PAL Dvd - 452Mb. To my eye, on a 19" Lcd, there is no difference in quality: is the Dvd really "better"? Would I notice the difference on a TV-size screen?

Thanks.

[GuyL]

I am amazed at the high quality of the finished video: it's almost as if VS9 is rendering only the transitioned areas - but that's not right, is it?

Yes it is if your have smart render enabled.

I'd like to understand what happens to a clip after editing and rendering to make it increase so much in size. Example: a 19 minute, 101Mb avi, when edited to 4 minutes with a crossfade between each clip (about 12, can't recall) rendered as Mpeg2 is 155Mb in size: how come?

AVI is just a container that could be using many different codecs. What "type" of AVI are you using? By the sounds of it, it looks like MPEG4 or DivX.

As far as MPEG it mostly comes down to the bitrate. The higher the bitrate used the larger the file.

[DVDDoug]

When you're converting to different formats it's "apples to oranges."

...project first as Mpeg2 - 305Mb, then PAL Dvd - 452Mb. ...there is no difference in quality:

Right ! MPEG-2 is a "lossy" compression scheme. You cannot increase the quality later, or get-back the lost quality, by increasing the bitrate or resolution. It would be like converting a low-quality MP3 into CD format... The resulting CD won't be "CD quality".

Or, imagine that you have an image that has a resolution of 720x480. That image is made-up of 345,600 pixels. If you squeeze that image down to a 32x32 icon, it's made-up of only 1024 pixels. If you blow-up the image to 720x480 again, you don't get back the lost detail. you get a bunch of duplicated (or maybe interpolated) pixels. (MPEG is smarter than that, but it does throw-away data.)


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With a given format, for example MPEG-2 which is used for DVDs:
Higher bitrate = higher quality = bigger file = less compression
Lower bitrate = lower quality = smaller file = more compression

And while we're on the topic, my "rule of thumb" is that you can fit about 1.5 hours of good quality video and Dolby stereo sound on a regular single-sided DVD. When I push it beyond 2 hours, I start to really notice the video degradation. But, you have to judge for yourself... There are many factors including the quality of the original, the size and quality of your TV, and how picky you are.

For the same quality, a AVI/DV file is bigger than an MPEG-2 file, and an MPEG-2 file is bigger than an MPEG-4.

However, the best AVI/DV file has better quality than the best MPEG-2, and I believe the best MPEG-2 is better than the best MPEG4.

If you convert from one lossy compression format to another, you loose quality. If decode and re-code in the same lossy format, you loose quality. For the best results, capture and edit in AVI/DV (not AVI/DivX!), and encode to MPEG-2 once before burning to DVD. See the Recommended Procedure.

[Ron P.]

I found this website the other day and I think it has some good information and explanation concerning this.

http://www.cybercollege.com/tvp047.htm

Regards

Ron P.

[sjj1805]

I was enjoying a read of all that until I suddenly came across the compulsory TEST
Joking aside, interesting article and confirms what I've been suspecting will be coming along in the near future, particulary memory card storage.
Didn't like the idea of carting a Hard Drive round though, that would be heavy, OK for a few hours but if you were on holiday imagine carrying it all day.
On the other hand memory cards would be very light. Look at those SD cards in digital cameras - the size of a postage stamp and can hold 2GB of information already. another plus side is the ability to simply take the card out of the camcorder and drop it into a card reader for almost instant transfer.
Less wear and tear on the card - no moving parts unlike the alternatives of tape, hard drive or DVD disc.

Steve J

[GuyL]

Like Steve, I enjoyed the article and the next gen storage really is interesting. However, I think we are a long ways off yet. They work today but the cameras have to store in very compressed formats which makes editing this content very difficult.

If you want to shoot and transfer then that is fine but the media will have to have the capacity of tape before it can be used for any editing.

[sjj1805]

What a co-incidence. My daily cnet newsletter has the following headline article:
Member Question of the Week
I recently read an article by a data storage expert who claimed that burned CD-Rs and CD-RWs can be expected to last only two to five years

http://nl.com.com/view_online_newslette ... st_id=e497

You may have to sign up to read it, don't know though as obviously I am already a member.

Steve J