Author Topic: Compression Help Please  (Read 1997 times)

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Jake_82

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Compression Help Please
« on: January 20, 2003, 03:13:47 PM »
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I'm trying to compress a 10:30 long video so I can upload it and put a link to it here... I tried using DivX at 1-pass 200kbps for 320x180 and it looks fine but it ends up being 130 mbs or so, and I only have about 70 megs on my server, plus I doubt anyone wants to download that much for only 10 minutes of video... what do you guys suggest? I'm using Premiere 6.5 by the way
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Jake_82

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Compression Help Please
« Reply #1 on: January 20, 2003, 03:21:13 PM »
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Nevermind, I figured it out... I got it down to 30 megs so I'll upload it in a couple hours  :D
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sphinx

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Compression Help Please
« Reply #2 on: January 20, 2003, 08:58:08 PM »
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Quote from: Jake_82
Nevermind, I figured it out... I got it down to 30 megs so I'll upload it in a couple hours  :D


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Xixax

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Compression Help Please
« Reply #3 on: January 20, 2003, 09:04:29 PM »
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Might want to think about also using the Windows Media Export feature of Premiere. It'll squeeze files down nice and small, and no extra codecs are needed.
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kotte

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Compression Help Please
« Reply #4 on: December 31, 2004, 02:00:46 AM »
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I've compressed a 40 second 150 MB video clip down to 6,8 MB with a decent quality.
Why is it that when it has 8 seconds left the picture kinda fast-forwards by itself? Leaving the audio playing over white at the end. Happens only with Sorensen. This has happened on several clips.

matt35mm

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Compression Help Please
« Reply #5 on: January 17, 2005, 08:36:04 PM »
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What gives a higher quality image: one pass or two pass?  I don't really know what that means.

Also, if anyone knows how to get the highest quality image for a DVD using something like Apple's Compressor, I'd appreciate the help.

matt35mm

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Compression Help Please
« Reply #6 on: January 18, 2005, 10:59:02 PM »
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... I have to burn this DVD tomorrow.  I'd really like it to look the best it can.  Can anybody help?

ono

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Compression Help Please
« Reply #7 on: January 19, 2005, 02:09:44 AM »
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I think one pass is higher quality.  Don't hold me to it.  Thinking logically, a "pass" sounds like when the program compresses a file.  A file only compressed once will have better quality.

kotte

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Compression Help Please
« Reply #8 on: April 16, 2005, 03:22:40 AM »
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I've had a lot of headaches over compression. Didn't know how to do it right. I didn't know how and in what program etc. And what's a good data rate bla bla bla.

This tutorial and Quick Time Pro is all you need (the tutorial anyway)...

The key to getting good compression is to understand the concept of video data rate. The data rate is how much video data is stored for each second of video. If you have a 1 minute video clip that is 60 MB, then the data rate is 1 MB/sec (60 MB/60 seconds). In your case, you are using 500 MB to store 7 minutes of video (actually, some of that 500MB is audio, but we'll ignore that for now). So your data rate is 500MB/420 seconds = 1.2MB/sec.

There's no such thing as the "right" data rate. Whether a data rate is appropriate depends on what you are going to do with the video. 1.2MB/sec is a great data rate for DVD video. For web video, it's terrible. In general, you have to make a trade-off between resolution, quality, and filesize. For web video, I use a rule of thumb that one minute of 320x240 resolution should take no more than 5 MB. I find that this gives decent quality without sacrificing too much resolution and filesize. For your video, that would mean 7 * 5 = 35 MB for your entire video. You'll need to decide whether that's small enough. I'll assume that it is. Then our data rate is 5MB/60 seconds = 83.3 KBytes per second. That is what we will use to control our filesize.

That only includes the video. The audio is separate. The latest version of Quicktime Pro supports exporting in MPEG-4 format. I strongly suggest using that. To save space, choose a sample rate of 22.050 KHz and Stereo (stereo sound is worth a little extra space, but if you know that your sound is mono, choose Mono instead). Click the Options button, and choose 64kbits/second for your bit rate. The bit rate is like the data rate: how much data to store for a second of audio/video. 64kbits/second is a good tradeoff.

For the video settings, set your size to 320x240 (or equivalent, if you using other than a 4:3 aspect ratio). For compressions, select Sorenson video. Choose Best for quality (we are controlling size via the data rate, so we want the encoder to do the best it can with that date rate). Choose the frame rate that matches your video, probably 29.97 (don't try to save space by reducing the frame rate; all of our space savings should come from choosing an appropriate data rate). For the keyframe setting, set it to match the frame rate (round 29.97 to 30), so that there is a keyframe every second. This will keep your video smooth as it plays. Then do the most important part: check the "Limit data rate to" box and enter 83 in the box to set your data rate to 83 KB/sec. Click OK, and save your file. If you've done everything right, you should end up with a 35MB file (maybe a little bit bigger because of the audio), just as we intended. If you are happy with the quality of the output, then you're done. If not, you can increase the bitrate to improve quality (at a cost of space).

 

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