There are various reasons why you might want to compress a video; perhaps you'd like to send it to someone by email, or maybe you need to free up some space on your hard drive. As many different reasons as there are for compressing files, there's also a large number of options to choose from and various file formats that the original video may be converted into. What we'd like to do here is give you a quick explanation of what video compression actually is and the factors you need to consider to get the best results.
What is it?
Depending on the length and the resolution of the videos you record, video files can easily get quite large, taking up several gigabytes of storage space on your computer's hard drive. At that point, if you want to send them to someone via email or upload them onto a website, they're often too large. If you want to reduce the file size of a video, compression is one of the options available. When you record a video, you're typically recording 24 frames per second; the rapid succession of these images is what the eye perceives as movement.
But since these 24 frames per second are so close together in time, only a small portion of each individual frame actually changes, and not the picture as a whole. Compression takes advantage of this feature, and instead of storing each individual frame, it only stores the changes that occur from frame to frame, as perceived by the program you're using. Reducing the amount of data involved ultimately results in a more compact file size. This allows very large video files to be converted into significantly smaller ones, depending on the compression rate. This will, of course, also have an effect on the quality of the picture.
What kinds of video compression are there?
If you want to use compression to reduce the size of a video file, there are several different options to choose from. One question you're going to want to ask is which format you want to end up with. You should base your decision here on finding a format that's recognized by as many different systems and programs as possible. One such video format would be MP4.
Then there's the question of resolution: If a video's only going to be viewed on mobile devices anyway, it's not necessarily going to need to be in 4K with 3840 x 1260 pixels; even a full HD resolution of 1280 x 720 would be too large in this case. But naturally, reducing the resolution causes a decrease in picture quality, sometimes quite drastically, and this cannot be reversed. For this reason you should always hold onto the original video file until you're absolutely sure you're satisfied with the compressed version. But if you want to reduce the size of a video file without any loss in quality, you should probably stick with the resolution from the original file.
What are the bit rates for various media formats?
- Standard audio CD: 1.4 Mbps
- Standard-definition TV: 3.5
- Mbps 720p mkv file: 8 Mbps
- High-definition TV: 8-15 Mbps
- Standard-definition DVD: 9.6 Mbps
- 1080p mkv file: 12 Mbps
- Blu-ray Disc: 20-40 Mbps
One more important issue when it comes to video compression is the codec you use. A codec is a certain pair of algorithms that work together to code and decode the data. Different kinds of codecs use different base formats and setting options, so they be a significant factor in the size of the compressed video file. When it comes to choosing a codec, once again you should try to use one that's recognized and supported by as many systems as possible, H.264 being one such codec.
Bit rate has to do with how fast the data is transferred. As such, it's measured in bits per second (bit/s), which of course lets you know many bits are transferred each second. The bit rate can be changed during the process of video compression; as a rule, the higher the bit rate, the higher the picture quality, and as such the larger the file.
Sound also has a certain role to play when reducing the size of a video, of course, even though when it comes to file size, audio tracks are significantly less substantial compared to video files. If your video has as soundtrack in WAV format, you're going to want to compress it along with the rest, and should opt for MP3 with a rate of 320 kb/s. The quality of this audio format is in most cases more than good enough, and the file size is much smaller than you find with WAV files. Particularly in the case of longer videos, this will have a noticeable impact on the eventual size of the file. Of course you can also reduce the file size of MP3s themselves (down to say, 128 kb/s or 96 kb/s), but this will have a perceptible effect on the sound quality.
As you can see, there are several different factors that go into video compression, but our video compressor Movie Edit Pro will do most of the work for you and help you convert your videos in no time.