Compression of Video files - massive reduction in size!

[bus_ter]

I noticed that my captured videos from the webcam using Sharpcap are rather large.

A 3 minute capture in 640x480 at 15fps is a whopping 1791 MB in size!

It occurred to me that you can download a DVD film in DVD quality at 30fps, 2 hours in length for about 700MB.

Webcam footage is comparatively *very* low quality, and should compress well without losing any noticeable quality.

So I did a compression of my capture file (divx), keeping the same resolution and fps. The resultant file ..... 6 MB!

I played the files together and they looked identical. I then ran the new 6 MB file through Registax with the same settings. Resulting file looked exactly the same!

So my questions is. Why are we dealing with massive file sizes of very low quality video? Captured video quality is so low that it can be compressed right down without losing any visible detail.

[GlassWalker]

How long did it take you to convert the original file to divx? Codecs like that are computationally intensive, so you need to have the right hardware to back it up if you want to do it real time. Also it is still lossy. I've wondered about a half step, of using lossless or near lossless compression. There are many lossless schemes, which wont offer as much space savings a lossy format would allow, but still offer a tangible space saving with relatively low computational cost.

Personally I'd like to have the best data available to start with. If you wish to store the file long term and want to reduce its space requirements, then perhaps the right choice of compression is appropriate.

[bus_ter]

Only took about 60 seconds to compress the file. There is by definition a loss of information, but in practice it's so small I can't tell you which stacked image came from the 6mb video and which from the 1791mb video! A little like saving a Raw/TIFF image file as a .jpg. You have to look really hard to see any difference.

If nothing else it gives people the opportunity to upload their video files for others to process. I've already done that tonight, and it's interesting to see what others can do with your capture.

[themos]

Yes, you can compress video because the human eye is not sensitive to much detail when the images are moving. What we are trying to do is to combine all these frames in one static image and then the eye will see the detail. If you start compressing the video, at some point you will lose that detail and you cannot know beforehand when to stop compressing. Incidentally, that's why we don't push the cheap USB1 webcams to frame rates higher than 10fps (although they are capable of it), we can't afford the compression.

[jimmyjamjoejoe]

As said above, compression on the fly is very cpu hungry. For stacking etc, you may as well keep the original, since even the tiniest details will be brought out. However if you're storing the video for nostalgic reasons, or wanting to upload the video itself, you'd be amazed how much compression you can get with a decent codec like h.264.

I used to record 1080p game footage via fraps, and h.264 would crunch several gig to around 100mb, while retaining hd resolution without noticeable quality loss.

[Cath]

Any lossy video/image compression will remove fine data (and not so fine data/details) from your images/videos and replace it with compression artifacts (unwanted).

If your going to compress your video before working on it, then you must use a lossless compression if you don't want to loose data/information. I use HuffYUV compression (codec) if I need to compress video files before/while working on then. I have regularly worked with 60 to 80GB video files, so your 1.791GB file is actually nothing when it comes to video files/editing.

Canon CR2 raw image files use compression, but it's lossless jpeg compression, which is fine.

Lossless compression doesn't reduce the file sizes anything like lossy compression does but that's OK, because when/if you come to upload your final video to the internet you would then be fine to use a lossy compression scheme (if it's purely for viewing, such as youtube, vimeo etc).