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Why are my file sizes so different?
September 10, 2010 9:58 AM   Subscribe

I'm having a problem with screen recording software on Windows XP.

I have two identical computers, both of which have been recently re-formatted and had fresh installs of Windows XP. I am using them to record screen video of both sides of IM conversations. I am using the open source program CamStudio to record the screen activity. Both computers have identical settings in CamStudio.

Here's the problem: Computer A will produce an .avi file of about 500MB for an approximately 30-minute video; the *same* 30 minute conversation on Computer B is producing .avi files of 1.5-1.6GB!

Why is the second computer producing such large file sizes? I'm concerned in part because CamStudio documentation can only handle file sizes up to 2GB, and I'm worried about corrupted files (this is part of a research project). I'm concerned that the massive discrepancy in file sizes is indicative of a larger problem that could cause the computer to fail in the middle of a session.

I am a Mac person, and I inherited these computers (they are probably more than 5 years old), so I'm not as adept at Windows troubleshooting.

Please hope me MetaFilter!!
posted by DiscourseMarker to Computers & Internet (12 answers total) 1 user marked this as a favorite
 
Are you capturing the whole screen or just individual windows? Are both desktops at the same resolution? What about color depth?
posted by Rhomboid at 10:16 AM on September 10, 2010


Both are currently set to the same resolution (1152x864) and color quality (highest). I am capturing the full screen on both computers.
posted by DiscourseMarker at 10:21 AM on September 10, 2010


In that case it sounds like different codecs are being used to encode the files. I know you said the settings in CamStudio are the same, but if there are different codecs installed on the two machines then CamStudio might be choosing differently based on some heuristic. Run the video files through something like Mediainfo and look at the type of codec, framerate, and bitrate. A program like Gspot will show you the list of installed codecs on each machine so that you can look for differences.
posted by Rhomboid at 10:42 AM on September 10, 2010


Thanks Rhomboid--I will investigate the codecs and see what I find.
posted by DiscourseMarker at 10:47 AM on September 10, 2010


Oh and anti-aliasing (what Windows calls 'font smoothing') and/or subpixel rendering (what Windows calls ClearType) will make a huge difference in compressibility of text, so that would be another thing to check, in the display properties page.
posted by Rhomboid at 10:48 AM on September 10, 2010


We ran Gspot--I'm not sure I quite know how to interpret the results. Here is Computer A (the smaller files) and Computer B (larger files).

Also, I was looking under Display Preferences (at least I think I was) but couldn't find anti-aliasing--but perhaps I was looking in the wrong place.
posted by DiscourseMarker at 3:01 PM on September 10, 2010


The larger file is encoded at 9505 kbit/s and the smaller one is encoded at 2513 kbit/s, so that explains the size difference. But more worryingly than that is the these clips seem to be encoded with the FOURCC 'CRAM' which is Microsoft Video 1, a codec which is obsolete garbage from 1992, a legacy remnant of Windows 3.1. You really don't want to be using that codec, as it probably has little to no sane bitrate control. If you can switch to something more modern your file sizes should be a lot smaller and more consistent. For example WMV9 has a profile for screencasts, called "Windows Media Video 9 Screen" with a FOURCC of 'MSS2'. I would have thought that CamStudio would have installed its own screencast-optimized codec as well, but if you are going to distribute this to other people for viewing you probably don't want to use that. Look again through the encoding options for the codec selection -- it may be hidden away under advanced settings. If you can't figure out the settings in CamStudio then another option is to just produce uncompressed streams and use a different tool to encode and compress the video with a modern, proper codec after the fact.
posted by Rhomboid at 10:07 PM on September 10, 2010


I'm pretty sure that CamStudio had at least a few options for video codecs--I'm not at work now so I'll have to check on Monday. If we change toe codec in the CamStudio preferences, will that override the use of the old Microsoft Video 1 codec, and fix the bit rate issue?
posted by DiscourseMarker at 10:08 AM on September 11, 2010


Yes, the codec choice is exclusively in the hands of the encoding application, although you can always re-encode the files afterward if you can't get CamStudio to cooperate, although if it comes down to that you'd be better off setting CamStudio to output uncompressed video or a lossless codec so that you don't have a double quality loss by compressing it twice. I don't know if it will fix the bitrate issue -- it could be that the ancient CRAM codec had incredibly poor bitrate control and that is what was causing the disparity, or it could be some as-yet unidentified difference. Choosing the right codec can be a very complicated process that involves details your workflow, what kind of visual quality is acceptable, whether the file will be streamed, who your intended audience is, how they will be getting the video, what kind of OS and software they will be expected to have, and so on.
posted by Rhomboid at 11:18 AM on September 11, 2010


CamStudio has 4 options: Cinepak Codec. Radius, Intel Indeo Video 4.5, Intel IYUV codec and the Microsoft video 1 that is what it was previously set to, and what seems to be the default.

These videos will be mostly used by me; I need pretty clear recordings to be able to make transcripts of people's screen actions. I may also want to display excerpts at conferences, so a quality that would wok ok for projecting would be nice. The videos won't be streamed or otherwise distributed, except to 1 or 2 other members of my research team.
posted by DiscourseMarker at 11:12 AM on September 13, 2010


Yikes. Those are all pretty much all ancient and horrible. That tells me that CamStudio is using the VFW API, because if it were using DirectShow you would at least expect to see options to encode in WMV9 which is by default included with Windows. But if it's mostly for your own use then I suppose it's not that big of a deal. Indeo 4.5 sounds like the best of the bunch, but try experimenting with them and see which ones give you the best results.

Also, about the anti-aliasing settings: in XP it's under Control Panel -> Display -> Appearance tab -> Effects -> "Use the following method to smooth edges of screen fonts". If you're using LCDs then you probably want that set to ClearType for the most readable fonts (see also ClearType tuner) but even if you're using CRTs then having anti-aliasing enabled (i.e. font smoothing = yes) would be a good idea. But for encoding screencasts it could go either way -- a modern DCT based codec would probably do better (i.e. smaller file size) with anti-aliased fonts, but MS Video 1 (and likely some of those others on the list) would probably do a better job with anti-aliasing disabled due to the fewer number of colors.
posted by Rhomboid at 3:45 AM on September 14, 2010


So my research assistant and I spent 2.5 hours fiddling with these yesterday, to no avail. Turns out Intel 4.5 codec produces files we can't open, and the other Intel codec wouldn't work at all (we got an error message when we tried to record). We tried a different free program, HyperCam, but it had the same codecs and the Cinepak coded on both programs gave us smaller and consistent file sizes, but the quality was not good enough for what I need.

So now I'm going to try a new, up-to-date program, Camtasia 7, and keep my fingers crossed that it will run on these machines (Camtasia says you should have a minimum of 1GB RAM, which is exactly what we have installed).
posted by DiscourseMarker at 7:43 AM on September 14, 2010


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