[Czachorski]

I have been archiving my old analog videos to DV using Dazzle Hollywood DV bridge to bring them into iMovie, and from there, I am exporting to quicktime with the mpeg4 codec at 320x240 & 30 fps for archiving purposes.
I am using my sony hi-8 comcorder to play through the bridge. When I was converting footage from my very old 8 mm camcorder (regular 8 mm tapes) the mpeg4 .mov files were running about 2 GB per hour. Now I am converting hi-8 tapes that were recorded on my hi8 sony, and the mpeg4 .mov files a running about 2.8 GB per hour. All the export settings in iMovie were identical for both tape types.
Is the mpeg4 codec using some type of variable bit rate encoding, or does it somehow recognize that there is more information in the hi8 source, and therefore is increasing the sample rate? This was kind of surprising to me, since I expected the file size to be consistent, regardless of the soruce. Any ideas? I am always interested in learning how DV works. Thanks!

[geek_rock]

this doesn't really make sense.. you're exporting to 320 x 240 videos, and your files are coming up at 2 GB per hour? that's way too much for that size video. you should lower the bitrate way down, and make your video about 200 MB an hour. i doubt you'll notice much difference, not at that resolution.
-Mark

[Czachorski]

Hmmmm - with what Codec and what frame rate? I am just choosing the "expert" quicktime export from iMovie with mpeg4 codec at 320x240 and 30 fps. The source is a VHS camcorder tape, and the mpeg4 is 99% of the quality of the original by my eye. The resulting file size is about 2 GB per hour.
Based on your comment, I did try the export from iMpovie using the "CD-Rom" option, which uses the H263 codec at 320 x 240 and 15 fps, and was about 500 MB per hour, but it looked like absolute crap. The resolution was much worse than the mpeg4 and the 15 fps made the video look quite choppy.
If there is an export setting from iMovie that could give me the same quality as the mpeg4, but at 1/10th of the file size, I would love to start using it. Do tell, please.

[geek_rock]

use the mpeg-4 codec and 30 FPS. all you're doing is changing the bitrate.
in imovie go to file > export.. > and export to quicktime with expert settings.
in the next window press the "options" button and then click the video tab. use the slider there to change the bitrate.. it's basically like mp3 bitrates only on a larger scale.
try something like 300 kbits/second to begin with. if you're happy with it, fine.. if not up it to 350.. and so on.
you might want to try it on a tiny file clip first, so you can see how the results look.
at 300 kbits/second you'll end up with 3 MB or so per minute of footage.

[Czachorski]

Well, I played around with limiting the data rate, and I think that you have been a little optimisitc with your math. At 300 kb/s, I am getting a file size of about 1.2 GB per hour, or about 20 mb/s, not the 3 mb/s that you estimated. The movie at 300 kb/s looks about as 95% as good as the movie without a bit rate limitiation (resulting in twice the file size). So it comes down to a simple optimization question - is it worth it to have 95% of the quality at half the file size? For me, since I have plenty of HD space (380 GB) and these are critical videos, I am going to take the larger file size with the slightly better quality.
Regarding your math, doesn't a data rate of 300 kb/s x 60sec/min = 18000 kb/min, or 18 mb/min?? (not the 3 mb/min that you estimated) This is essentially the file size that I am getting with limiting the data rate to 300 kb/s. It seems like your estimates, and my files sizes are off by a factor of 8. Did you do something funny with a bit versus a byte or something when you made your calculation? Am I doing something wrong here, either with my math, or with my settings?
I can achieve a file size of 3MB/min at a data rate of 50 kb/s, and although it is quite impressive looking for such a small file size, I would say that at this bit rate, the video quality is only 60% as good as the original, which is unacceptable for my archives. However, I am impressed with the quality of this setting for the file size, and could see using it to email clips to people or to post videos on the web. So, overall thanks for the tip!!!

[geek_rock]

hmm.. this is sounding mighty confusing now.
i just exported from imovie using mpeg 4 codec, (320 x 240, 30FPS) with these settings..
video track - improved, 300 kbits/second
audio track - 128kbits/second, 44.1 khz
i exported a 30 second clip and my overall file size is 1.4 MB. which would be = 60 seconds = 2.8 MB (rounded down figures).
quicktime says my video track has a data rate of 33.3 k bytes/sec, and the video track has 15.6 k bytes/sec.

[Czachorski]

A few items to note -
I am using iMovie2. The mpeg4 settings that I get give me a quality setting choice, which I am setting to good, which is one notch below the "best" setting. I opened the movie that I exported with a bit rate of 300 kb/s and quicktime said that the bit rate was like 297 kb/s.
To address my original question at the top of this thread, I checked the bit rate of the videos that I exported to mpeg4 without any bit rate limitations. For the footage from my 8 mm camcorder that had a file size of about 2 GB/hour, quicktime says that the bit rate is 738 kb/s, and for the footage from my hi-8 camcorder, quicktime say that the bit rate is 869 kb/s. Strange that these bit rates do not multiply out to match the files sizes that I am getting (off by about 50%), but it does raise an interesting point - somehow when I export to mpeg4, the codec is recognizing that there is more information in the DV stream file captured from hi-8 and increasing the bit rate accordingly. Very interesting.

[halo_echoes]

i have no idea what is causing the problem, but you definitely shouldn't be getting nowhere near those large file sizes for mpeg4 video. the file sizes geek rock posted are about what you should be getting.
what version of quicktime pro are you running btw? from the description of your mpeg4 export settings, it sounds like you're still running 6.0. if this is the case, you may want to consider upgrading to 6.1 as a start, they integrated more advanced mpeg4 export options to the most recent version.

[Czachorski]

Yes I am on QT 6.1
I guess I am puzzled why both of you keep making that comment about the files sizes. The files sizes I am getting are exactly equal to the bit rates that I am setting. At 300 kb/s, I am getting 300 x 60 = 18,000 kb/min or 18 mb/min, which is about 1 GB per hour. (BTW - this is much, much smaller than native DV stream which 200 mb/s or 12 GB per hour) What size files are you saying that I should be getting at 300 kb/s, besides 300 kb/s?????????
I really do need a more technical explanation than "those files sizes are big, I don't know what you are doing wrong......" I can see my math being wrong, and I can see my computer screwing something up, but is it some kind of amazing coincidence that I am setting my bit rate to 300 kb/s and my resulting file size for a 1 minute clip is coming out at 18 mb, which is 300 x 60 / 1000 ?? This seems to make sense to me.
I would be very interested to know what file size you get when you export a 1 minute DV stream file to mpeg4 with a bit rate limitation of 300 kb/s. And then, what is the proper math to compute that file size. Maybe I have some double error somewhere in my computer and head. /forums/ubbthreads/images/graemlins/confused.gif

[geek_rock]

all i know is, i used these settings:
quicktime setting screenshot
(video - 300, audio - 128)
and my files are coming out at about 3 megabytes per minute.
maybe you're doing your maths wrong or something.. but if you use these exact settings in imovie then you should end up with the same sized file as me.

[Czachorski]

Thanks for the screen shot. Very interesting, because my export dialog box dosn't look like that. It is close, but not exactly. Is that QT 6.1 in OS 10.2.4? That is what I am running. I posted a screen shot at this web page. Take a look. See what I mean. A little different. Weird, eh? (Yeah, I know it says 500 kb/s on the screen - I was playing around with different settings).
What was the source of your video? Based on the playing around that I have done with exporting to mpeg4, if your source is a low bit rate, your export will be a low bit rate. Perhaps your source was about 50 kb/s? Or was your source DV stream footage from a digital camcorder, or some other format?
I am very curious about this, since I am relatively new at all the DV stuff, and I am very much interested in understanding all of this. Where is Daft&Dewey-eyed when you need him???? Help!!!!

[geek_rock]

hmm.. are you running quicktime pro or just quicktime? i've got pro, maybe that has something to do with it..
now somebody correct me if i'm wrong.. but i was under the impression that dv is a standard bitrate no matter what the source is originally - so if you ran a dvd player thru the dazzle, or a vcr, or a camcorder, or whatever, your resulting files' bitrates would be all the same..
this is getting way confusing now.. maybe someone else can shed some light? /forums/ubbthreads/images/graemlins/crazy.gif

[Daft&Dewey-eyed]

Well, this is a rather interesting discussion, and I don't know that I'll really be able to shed any light on it, but here's my take:
The DV format is a compressed video format. DV compression is a fairly mild 5 to 1 compression with 4:1:1 color sampling (although color sampling is not exactly germane to this discussion). DV has a constant data rate of about 3.6 MB/s (25 Mbps). DV compression is accomplished in real time by a hardware chip in a camera or DV bridge like the Dazzle or Canopus devices.
When you recompress your DV file using another codec, new rules apply to it. Each new codec has its own way of doing things. The MPEG codecs work by essentially capturing the first frame of a shot in full resolution and then saving only the parts of the remaining frames that are different from the first frame. This makes MPEG compression very efficient, but quite difficult to edit.
File sizes will vary in MPEG compression for a variety of reasons. Scenes with more motion will have more information that changes in each frame, and will result in larger file sizes. It is also quite likely that the better footage from Hi-8 has something to do with the larger MPEG file sizes.
DV is a standard bitrate, but the images carried by the DV stream can still vary in quality and content. A different codec will recompress based on the picture content, not the bitrate.
2 GB per hour is not a terribly huge file size, particularly if it yeilds satisfactory image quality. It is certainly possible to achieve much smaller file sizes with the MPEG-4 codec, but quality will suffer. If you are looking for high quality images and not bothered by the file size, don't worry about it.
I won't comment about all the math being bandied about, because I'm really rotten with arithmetic.