Reducing Video File Sizes
Size does matter. These three words ring especially true for video files. Video files are among the largest files there are on a PC. They fill up your hard disk, slow down your PC, get too big to copy to other computers. They can also be almost impossible to distribute over the Internet. Though the Internet bandwidth available is always increasing, and storage devices like large hard drives and DVDs become less expensive every year, a typical video continues to take up 'too much space'.
Today, there are a lots of video formats available. This article discusses three popular file formats, and some ways in which you can significantly reduce file sizes.
- AVI
- Windows Media Video (WMV)
- Flash Video (FLV)
Format Comparison
AVI stands for Audio Video Interleaved. This format has been around for some time. The AVI format is very flexible because you have a choice of several different compressors to balance file size against quality. It's also very easy to navigate and edit using software like
Video Edit Magic. AVI files are not a good choice for distribution because file size is simply too large, even with compression.
Before distribution, convert AVI files to a different format using
Digital Media Converter Pro. Both Windows Media and Flash Video are excellent alternatives when distributing video files.
WMV provides good quality with extremely small file sizes. It is one of the most popular choices for video email, web video, and permanent storage on a PC.
Flash Video (FLV) has become the format of choice for web video applications. Created specifically to use with Adobe Flash in web applications, it was designed from the bottom up for streaming over the Internet. Flash Video is rarely used for non-streaming applications.
AVI
You can get the best possible quality by using an uncompressed AVI file. However, uncompressed AVI files are enormous, too big to practically distribute or to store.
Some ways to reduce the size of AVI files are:
- Reduce the resolution
- Reduce the frame rate
- Change the compressor
- Changing Audio Settings
The article
Understanding Compression In AVI has an in-depth description of AVI compression.
Reducing the resolution
The "resolution" is the size of the video image, expressed in pixels (dots). The resolution of standard TV is 512 x 492 pixels, a US DVD 720x480, and high-definition TV (HDTV)can be as high as 1920 x 1080 . The higher the resolution, the sharper the picture. However, the higher the resolution, the larger the file size will be.
You can reduce the resolution of the original AVI file to significantly decrease the file size. When you reduce the resolution from 640 X 480 to 320 X 240, both the height and width are reduced by a factor of 2, reducing the file's size to ¼ of the original.
Reducing the Frame Rate
Digital video is actually a series of images, which change rapidly and give the illusion of motion. The frame rate is the number of frames displayed per second. The frame rate has a significant impact on the file size. US television has a frame rate of 30 frames per second (fps), while films in theaters are usually shown at 24 frames per second. Lowering the frame rate of your video to 15 or 10 fps can reduce the file size by as much as ½ or 2/3. However, reducing the frame rate may affect the smoothness of the playback. Acceptable frame rates vary depending on the specific video clip. You may have to experiment to find the lowest acceptable value.
Changing the compressor
Uncompressed AVI files are huge. AVI codecs (COmpressor DECompressor) greatly reduce file size while maintaining optimum quality. You can choose from the several codecs available from different sources. However, you should keep in mind that your audience must have the same codec to uncompress and view the file. Different compressors deliver different results. Cinepak Codec, from Radius, is a good choice for distribution to a wide audience, since it has the widest compatibility. (Cinepak is included with all versions of Microsoft Windows.) Xvid is a good choice for high
Changing Audio Settings
The audio portion of an AVI file can also be compressed. As with video compression, audio compression will dramatically reduce file size, by sacrificing some quality. In practice, high-quality audio compression often produces sound so close to the original that the difference is hard to detect. Very commonly-used audio codecs for AVI files include MPEG 1 Layer 3 (MP3) and CCITT µ-law (sometimes written as m-Law). For most codecs, you can also select the sample frequency. This is the number of times per second (ranging from 8,000 to 48,000 times per second) that the encoder measures sound levels. In general, the lower the number here, the more high-pitched sounds will be lost in the compression process, but also the smaller the final file size.
Reducing AVI file size using Digital Media Converter Pro
By changing these parameters with
Digital Media Converter Pro , you can greatly decrease the size of an AVI file.
To convert and reduce file size using Digital Media Converter Pro:
- Start Digital Media Converter Pro.
- On the File menu, select Add Files.
- Select the AVI file you want to reconvert to a smaller AVI file.
- On the Tools menu, select Settings.
- Under the General Tab, select Video Formats, then AVI as the Convert to Format.
- Select the Properties tab. You can change the parameters discussed in the preceding section from this window.
Now, you're ready to convert your video files into small AVI files. Select files for conversion and click the Convert button on the toolbar.
Windows Media Video
Windows Media Video files are created using pre-defined profiles that are configured for a specific distribution methods, for instance WMV For Desktop Viewing or WMV for Portable Devices. The Profile handles all the detailed settings like choosing a codec, frame rate, and so on. Profiles are pre-defined, and are designed to create extremely small files.
For example, to share a video over the Internet, you can select a WMV profile designed to create files for streaming from a video hosting server like
Video Desk.
To convert to Windows Media Format using Digital Media Converter Pro:
- Start Digital Media Converter Pro.
- On the File menu, select Add Files.
- Select the file you want to reconvert to WMV. You can also select an existing WMV file, and use a different profile that will produce a smaller file size.
- On the Tools menu, select Settings .
- Under General Settings , select Video Formats , then an appropriate WMV profile depending upon your distribution needs. For the very smallest video sizes, use WMV for Web Server . For the best balance of size and video/audio quality, we recommend WMV for Desktop Viewing.
Now, you're ready to convert video files into small WMV files. Select files for conversion and click the Convert button on the tool bar.
Flash Video
Flash Video was designed for use over the Internet, especially video hosting services like
Video Desk. Currently, FLV is the format of choice for Internet video, combining very good compression with good quality audio and video. This video format can also be played on almost any type of computer (Windows, Macintosh, Linux, and more).
When creating a Flash Video file, you select both an audio and a video bitrate for the file. These two control the size of the file, and also its quality. High bitrates make larger files with better quality. You may have to experiment to find bitrates that give acceptable quality with small file sizes. There is never a reason to use bitrates higher than those in the original file you are converting.
You should always use MP3 audio compression if you are trying to create small files.
File size can be especially important for FLV files, because they are almost all made for web playback. In many cases, you will pay your hosting service based on both the size of the files, and the amount of data streamed, so smaller files can directly save you money.
A final word: selecting the file format is the first decision you need to make when you want the smallest file sizes. Windows Media Video is a good, general purpose format. WMV files can be edited, played on a PC, or distributed over the Internet. Flash Video (FLV) is the most widely-used and widely-supported file format for Internet distribution today.