> > Formats and file sizes

Formats and file sizes

What kind and what size?

(Have a look at our Resources section for some useful software tips for working with images, audio, video etc ...).

What format should images be for the web?

Image formats for display on web page are:

  • JPG (for photos and images with lots of colours)
  • GIF (for logos and images with large blocks of the same colour)
  • PNG (similar usage to GIF. Unfortunately, different browsers vary somewhat in the way they display PNG colours and transparent areas)

Image formats that should under no circumstances be uploaded for display on web pages are:

  • TIFF
  • BMP
  • EPS ... etc

These are all designed for print usage, and will be both too large (and technically incompatible) for web usage.

Images for download purposes may be of any format, as these are intended to be downloaded by the user and opened using a different computer programme.

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How big should images for the web be?

Physical size

Generally speaking, websites tend to be optimised to display at a resolution of 1024 x 768 pixels, as this is the most common size of computer monitors currently in use. Therefore, 1024 pixels is normally the absolute maximum width for an image that you would like to display directly on a web page. In practice, as a single image is most unlikely to take up the entire width of the user's screen, images for web usage tend to be considerably smaller.

When websites are created, there is usually a style guide defining standard dimensions for images used on the pages.

File size

The file format, amount of colours and physical dimensions of an image can all effect the size of your image file.

However, as a rough rule of thumb, any single image that you intend to display directly on a web page should be smaller than 450-500kB. If images are any bigger, your web pages will load slowly in the visitor's web browser, impairing the general usage of the site.

Images for download purposes may be bigger, but bear in mind, the larger the file size, the slower the download.

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What format should audio and video files be for the web?

In contrast to images, web browsers do not automatically play audio and video files without a special 'plug-in'. Therefore, Firefox tends to open audio files using Apple's Quickime software (if installed), whilst Microsoft Internet Explorer will use the Windows Media Player by default.

It is important to note that by simply linking to an audio or video file, you cannot be sure that your users will be able to play it. For this reason, Content Curator uses a (Flash-based) player module built into the website to allow users to play media content. As long as the user's browser has the Adobe Flash player installed (this is extremely widely supported), then the user will be able to play the file.

The standard format for audio files is:

  • MP3

The standard format for video files used by Content Curator is:

  • FLV (Flash video files)

Other file formats (e.g. WAV for audio or AVI for video are not designed for web usage and are likely to be far too big to upload).

For help and information on converting media files to different formats, contact us!

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How do I compress audio and video files for the web?

Just like a JPEG image, audio and video files (MP3 and FLV respectively) provide you with the option to compromise the quality / fidelity of your recording for file size. The more the file is 'compressed', the smaller the file size, but the lower the quality. Remember, smaller file sizes mean faster download times and better usability.

MP3 Compression

The main factor in MP3 compression is 'bitrate'.

  • If your file is less that 5-6 minutes long, try using a bitrate of 192 kps. This will provide a good audio quality (in fact, your listeners are unlikely to notice any drop in audio quality at all).
  • If your file is longer that 5-6 minutes, try using a bitrate of 128 kps. There will be a moderate drop in audio fidelity, but the filesize will be comparitively smaller than the same file encoded at a higher bitrate.

FLV compression

FLV compression is considerably more complex than MP3 compression, and the options available to you differ wildly depending on the software you are using. In order to reduce file sizes, try reducing the audio quality (see above) or reducing the video bitrate.

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How big should audio and video files for the web be?

This is much more difficult to say than in the case of images, as the file size will depend on the length of your recording, as well as the quality in which the audio / video is encoded.

Generally speaking, however, any single file more than 30 Mb in size is placing a considerable burden on the server in terms of data transfer. Therefore, try to keep your files smaller than this.

NOTE: A 30 Mb MP3 encoded at 128 kps would be about 30 minutes long. A 30 Mb FLV video could be anything up to 10-12 minutes long.

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