WEEK 8 COMPRESSION

COMPRESSION

In this week lesson we looked at compression, what is it and the different types of compression available. The lesson started off by viewing our montages and receiving feedback on how to improve it. From this we went straight into video compression and individually asked to name some of the compression formats we’ve used or heard of, these are common ones:

  • H.264
  • JPEG
  • TIFF
  • MPEG2/4
  • FLV
  • GIFF
  • Microsoft AVI
  • MP4
  • WAV
  • Quick Time
  • MOV

So what is compression? Compression is when a logical file size is reduced into a smaller file, in order to save storage space. This makes it faster when transferring files from one network to another. With regards to video, there are in fact two formats to work with; file format and the actual video format. The file is the container for the video and is available in a wide range of formats such as : MOV, Jpeg, TIFF, PNG etc..

The video format is the type of compression that is being used to compress the video these include: Apple Proress, MPEG-4, H.264 etc.

Why do we have 2 formats?

In the lesson I learnt the reason why we have two file format is because the two formats one that’s is different.

  • The file format mainly decides what type of player will be able recognise/understand the format  in order to play the video
  • The video format decides what type of player will be able to play/understand the video file, in addition also the quality of the video.

We needed to know as there’s no one format that works on everything unfortunately. Therefore we a required to know what platform it is going to be played on. This will allow us to choose the appropriate file format or choose the appropriate video.

Compression can be characterised by two different codecs; lossy and lossless.  A lossless codec is one that maintains the quality of the video to a 1 to 1 compression. Whilst a lossy codec does not preserve the quality of the video.

The data rate of compression is the rate of which data (bits) its transferred. Bit rate is one that is measured in bits per second, but has higher denominations (Kbps and Mbps).

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HOMEWORK 

This weeks homework was to compress the montage video created in the previous lesson in order to see the difference in terms of quality. We were required to compress the video 4 different types of compressions on the video.

  • First compression: A lossless Compression (quality 10/10)
  • Second compression: A lossy Compression (quality 7/10)
  • Third compression: A lossy Compression (quality 5/10)
  • Fourth compression: A lossy Compression (quality 3/10)

First compression: This compression has a quality of 100/100, the filetype is .avi, this is a lossless compression therefore no quality loss. This has the largest file size. The reason why I did was to capture the original quality of the footage.

Second compression: This compression is set to a quality of 70/100, the filetype is .mov and the codec is .H264, the reason why i did this compression was to show that there is only negligible loss in quality whilst still saving disk space can be achieved.

Third Compression: This compression has a quality of 50/100, the filetype is .mov and the codec is Cinepak. The reason I did this to find a compression that is a compromise between file size and image quality.

Fourth compression: I did a lossy compression with a quality of 30/100, the file type is .mov and the codec is mpeg 4, I did this because I wanted to see how low a quality that I could achieve whilst maintaining a reasonable quality.

These videos were edited using After Effects. The following screenshots shows some of the process that was undertook to compress the video. I chose after affects because it was one that was available on my laptop even though I’ve gotten around to using Final Cut Pro. I decided this would be a good starting point to compress my video with the help YouTube tutorials.

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