What is Compression?

compressing

What is the point of Compression?

The point of using compression is to reduce the size of a data file, so that it takes up less space and is quicker to download.

Having uncompressed footage will take up a lot of space. Compressing the video before it is uploaded onto platform will reduce the size of the video so that it takes up less space. Uncompressed files hold a lot of different information within them and each data is encoded.

Here is a list of different file extension for video file format that can be used.

mov

avi

wmv .

mp4

mpeg

What is spatial compression?

Spatial compression looks at the algorithm in every single frame and compresses them in to an image. This will reducing the video file sizes by compressing the pixels within each frame independently.

A compression algorithm applied to a single frame of videoindependently, where the video image is compressed much like a JPEG image would be compressed”. Information from http://www.webopedia.com/TERM/S/spatial_compression.html

Example below

spatial-comp

What is temporal compression?

Temporal compression looks a series of frames over time and also motion. It will look at the Pixies that are the same and it will remember them if there are more frame that have the same pixies. It will also keep track of the changers over time. Also know as inter compression. Temporal compression space and time which makes the file size a lot smaller.

A type of compression used by some codecs that assumes framesbeside each other look similar. The first frame in the series would be entirely digitized (called a key frame). In the next frame only the information that has changed is digitized. Because temporal compression makes one frame depend on another it makes editing temporally compressed video difficult”. Information from http://www.webopedia.com/TERM/T/temporal_compression.html

Example below

temporal-compress

What is bit rate?

Bit rate is the amount of data contained within a second of the video. The higher the bit rate the higher image quality there will be in the video output. Also the higher the bit rate, the more data storage is required per second of video.

  “Remember that 1 byte consists of 8 bits. Video data rates are given in bits per second. The data rate for a video file is the bitrate. So a data rate specification for video content that runs at 1 megabyte per second would be given as a bitrate of 8 megabits per second (8 mbps). The bitrate for an HD Blu-ray video is typically in the range of 20 mbps, standard-definition DVD is usually 6 mbps, high-quality web video often runs at about 2 mbps, and video for phones is typically given in the kilobits (kbps). For example, these are the targets we usually see for H.264 streaming:
LD 240p 3G Mobile @ H.264 baseline profile 350 kbps (3 MB/minute)
LD 360p 4G Mobile @ H.264 main profile 700 kbps (6 MB/minute)
SD 480p WiFi @ H.264 main profile 1200 kbps (10 MB/minute)
HD 720p @ H.264 high profile 2500 kbps (20 MB/minute)
HD 1080p @ H.264 high profile 5000 kbps (35 MB/minute)

Below we recommend a few tools for detecting bitrate and codecs”. Information from http://help.encoding.com/knowledge-base/article/understanding-bitrates-in-video-files/

Example below,

bitrate

 

bit-rate

 

What is the balancing act with compression? i.e. file size/ quality.

Compression it is important because files that have been compression there data speed for transferring is increased, which means less time downloading and will also take up less store space.

The larger the file size the better image quality there it will have. The smaller file sizes the lower quality of image it will have.

Video takes up a lot of space. Uncompressed footage from a camcorder takes up about 17MB per second of video. Because it takes up so much space, video must be compressed before it is put on

the web. “Compressed” just means that the information is packed into a smaller space. There are two kinds of compression: lossy and lossless.

Lossy compression means that the compressed file has less data in it than the original file. In some cases, this translates to lower quality files, because information has been “lost,” hence the name. However, you can lose a relatively large amount of data before you start to notice a difference. Lossy compression makes up for the loss in quality by producing comparatively small files. For example, DVDs are compressed using the MPEG-2 format, which can make files 15 to 30 times smaller, but we still tend to perceive DVDs as having high-quality picture.

Lossless compression is exactly what it sounds like, compression where none of the information is lost.

This is not nearly as useful because files often end up being the same size as they were before compression. This may seem pointless, as reducing the file size is the primary goal of compression. However, if file size is not an issue, using lossless compression will result in a perfect-quality picture. For example, a video editor transferring files from one computer to another using a hard drive might choose to use lossless compression to preserve quality while he or she is working”. Information from http://desktopvideo.about.com/od/glossary/g/vidcompression.htm

“In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storage, handling, and transmitting content”. information from https://en.wikipedia.org/wiki/Lossy_compression

Examples below,

 lossy-1 lossless_lossy_compression_720 lossy lossy-compression-ratios-pic

 

Categories of compression – Lossless and Lossy

Lossless is used on Text or Programs

Lossy is used on image, video and audio

 

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