29/11/16 – Compression
When producing and exporting videos, one of the main features for consideration is the video format and the file format. These two terms are often mistakenly used interchangeably, however there is a distinct difference.
The file format is the extension to the end of the filename. Common examples in everyday life include .docx, .pptx, .pdf and .exe. Those more related to video and film include .mov, .flv, .exr, .tiff and .avi. The file format will decide what type of application can open, read and handle the file. For example, VLC media player can accept most of the common file types. Apple iPhones and iPads however cannot read or open flash files.
The video format, sometimes called the codec, determines how compression is added to the data itself. Common examples include Animation, Apple ProRes, H.264, REDCODE and XDCAM. The video format largely determines the quality of the file once it has been opened in an appropriate piece of software.
Some video formats are described as ‘lossy’, and others as ‘lossless’. This is because of the differing ways in which video codecs compress the files. A .raw image file is lossless, because the camera records all of the light information that the sensor records – this can result in very large file sizes. However, a .jpeg, for example, is a lossy format. As the file is compressed, some of the sensor data is thrown away. Under normalcircumstances, the effect is not noticed, and file sizes are greatly reduced. If the compressed images are enlarged too much, however, the result of the compression can be seen as the image would not be clear.
Another way to describe the quality of audio or video files is bitrate. This is a measure of the amount of data transmitted in a given amount of time, usually a second – either Kbps (Kilobits per second), Mbps (Megabits per second) or less commonly Gbps (Gigabits per second).
Below are four videos. They all have exactly the same content, but each is encoded with different settings. The first one is a lossless compression with a 10/10 quality. The next is a lossy compression with a 8/10 quality, and the remainder are lossy with 5/10 and 3/10 quality respectively. The difference that the compression makes should be clear from the buffering time when comparing each video, as well as the resolution of the video – especially when in full-screen mode.
Video 1: H.264 – Maximum Render Quality – 1920 x 1080
Video 2: MPEG-2 – HD1080p – 1920 x 1080
Video 3: Quicktime – NTSC DV Widescreen 24p
Video 4: MPEG-4 – 3GPP – 352 x 288
References and Further Reading:
- http://dt7v1i9vyp3mf.cloudfront.net/styles/news_large/s3/imagelibrary/V/VM_VideoCodecs_00.jpg?Lj9wdFfHHGdi92wy3Jqc1hoA1ZgM0ZOB=&itok=mwlGZIfv
- http://www.fallenempiredigital.com/blog/2013/02/08/a-guide-to-common-video-formats-containers-compression-and-codecs/
- http://tubularinsights.com/file-formats-containers-compression/
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