Using Camtasia to capture a thirty second video clip (Camtasia was unable to capture audio) of a television programme playing in actual size mode, which was 746 x 466 pixels in 16bit colour, in iTunes, I published this for various uses that were pre-set by Camtasia and obtained the following results:
|Original Capture File||CAMREC||329,468||749 x 466||15|
|DVD||AVI||294,190||720 x 480||15|
|HD||MP4||2,481||1280 x 720||15|
|iPad||MP4||1,104||640 x 360||15|
|iPhone||M4V||3,392||480 x 320||15|
|iPod||M4V||2,651||320 x 240||15|
|Web||MP4||976||640 x 360||15|
Given that each of these uses is designed for a target device with particular requirements guided by the resolution of the device and the format the video needs to be presented in, this results in different types of compression. “Compression is achieved when redundant data are removed for the video signal” according to Thapa (2010) and if we assume that the ultimate goal is perfect quality and zero network transmission time, the only way to approach this is some kind of compression or performance enhancement of the network and devices involved. Of course this is not achievable as limitations exist in all infrastructures, hardware and bandwidths, therefore we are usually faced with compressing files to a level of compromise that allows acceptable speed and quality.
From the above results, it is interesting to note that the differing resolutions for the same image formats do not necessarily follow a proportional file size pattern. This is due to the compression techniques used and the extra information that the file must contain for the target device or as Abomhara et al (2010) concluded that “each scalable video coding scheme seeks tradeoffs on the three factors”; efficiency, flexibility and complexity. It was also noticeable from the results that a particular format and resolution where a higher quality to the eye (another difficult quality to measure) was expected, such as HD, this was not the case due to the original capture resolution being lower than the conversion to HD resolution and therefore significant blurring occurred as Camtasia used the video’s complexity to amplify the size.
Overall the highest quality was provided by the DVD format AVI (an editing rather than production format with little compression) however even with an internal gigabit network speed, watching over a network caused interruptions as the file size over bandwidth was too large to be watchable. Therefore I found the best compromise was the web usage file as it remained at almost the original resolution, whilst with a small file size was perfectly acceptable to watch over a network.
Abomhara, M, Khalifa, O, Zakana, O, Zaidan, A, Zaidan, B, & Rame, A 2010, ‘Video Compression Techniques: An Overview’, Journal of Applied Sciences, 10, 16, pp. 1834-1840, Computers & Applied Sciences Complete, EBSCOhost, viewed 26 February 2011.
Thapa, G 2010, ‘Video Compression Techniques: A Survey’, IUP Journal of Systems Management, 8, 3, pp. 50-66, Computers & Applied Sciences Complete, EBSCOhost, viewed 26 February 2011.