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Files Types

Media files can be divided into four groups:

  1. Image compression formats (JPG, BMP, GIF, PNG)
  2. Audio compression formats (MP3, WMA)
  3. Video compression formats (MPEG 1, 2, 4; M-JPEG, WMV)
  4. Media container formats (AVI, MP4, ASF, WMA)

1. Image compression formats

The aim of image compression formats is to reduce the picture size, while not affecting the quality of a picture much. This is reached by reducing redundancy in the picture data.

Popular files are JPEG, BMP, GIF or PNG.

a. JP(E)G (Joint Photographic Experts Group)

JP(E)G stands for Joint Photographic Experts Group. It is the file format which is used by digital cameras to store pictures. In that sense it is the most important file format for digital photo frames. Furthermore it is widely used for publishing photographs in the internet. For photographs it is the ideal format, compared with GIF and PNG. GIF can just display 256 colours, while PNG files are much bigger than JPEG files. However, for linear drawings or text, PNG and GIF are more suitable.
JPEG is an ISO standard, which was created in the early 1990s. Usually, JPEG files have the file ending .jpeg or .jpg.

b. BMP

BMP files are used by Microsoft Windows to display graphics. They are typically not compressed, resulting in a large file size. Therefore, BMP are not used on the internet.

c. GIF (Graphics Interchange Format)

GIF (Graphics Interchange Format) are usually used on the internet for simple drawings, text or icons. The colors are limited to 256. In contrary to JPEG, it allows animations.

d. PNG

PNG is the third most usual format for images on the web and is similar to JPEG.

2. Audio compression formats

Audio compression has the aim to reduce the size of audio files. They use an algorithm (codec) to reduce the size.

Popular file types here are MP3 and WMA.

a. MP3

MP3 (correct name: MPEG-1 Layer III) compresses audio on a CD by a factor of about 10 while not affecting the quality much. Most people consider the quality of a MP3 is quite good, and therefore it is widely used, especially on the internet. Normal MP3 have a bit rate of 128 Kbps (kilobits per second). However, also higher bit rates, meaning better quality, exists.

b. WMA (Windows Media Audio)

WMA is similar to MP3, however, by far not that popular. A difference is that WMA can optionally support digital rights management.

3. Video compression formats

Video compression has the aim to reduce the file size of videos without losing much quality. Popular formats are MPEG 1, 2 and 4, MJEPG and WMV.

a. MPEG 1

This is a group of audio and video coding and compression standards. It was developed by MPEG (Moving Picture Experts Group). The video codec is used by the Video CD (VCD) format, while the quality approximately equals the quality of a VHS tape. The MPEG-1 audio layer 3 is the correct name for the famous MP3 audio format.

b. MPEG 2

MPEG 2 is a standard for audio and video coding. It is widely used for digital television. They are also used by many HDTV broadcasts.

c. MPEG 4

MPEG 4 should not be confused with MP4. MP4 is just one part of MPEG 4, namely MPEG 4 Part 14.
MPEG 4 are, like MPEG 1 and 2, standards for audio and video coding. Xvid and DivX are popular MPEG 4 codecs.

d. M-JPEG (Motion JPEG)

M-JPEG is a video format, where each video frame consists of a JPEG image.

e. WMV (Windows Media Video)

WMV are video codecs developed by Microsoft.

4. Media container formats

A container is a file, which contains other files. The container itself is used to identify and interleave the different files. WAV is a container just for audio, while TIFF is a container just for images. Several container for videos exist. They may be able to support audio, video and subtitles. The most popular video containers are AVI, MOV, ASF and MP4. Although MOV is used on digital cameras (at least at my Nikon camera) for videos, I have not seen a digital photo frame that supports MOV so far. MOV is the QuickTime container.

Because containers are just there to identify the underlying data, it may happen that a digital photo frame that supports AVI, does not play a AVI-movie. This can happen, when the underlying audio or video codec is not supported by the DPF.

a. AVI (Audio Video Interleave)

AVI is a video container developed by Microsoft in the early 1990s. Although having some limitations, AVI is very popular, especially for sharing file in the internet. AVI is supported by many video software programs.

b. MP4

MP4 is part of MPEG 4, its correct name is MPEG 4 PArt 14. It is a container format standard developed by Motion Picture Experts Group. Most MP4 files have .mp4 extension, while some, just audio file containing files, may have .m4a extension. Apple's iPod and iTunes use .m4a for audio files and .m4v for video files.

c. ASF (Advanced Systems Format)

ASF is another file container developed by Microsoft.

d. WAV (Waveform audio format)

WAV is an audio container developed by Microsoft and IBM. Most WAV files contain uncompressed audio data. Therefore, their file size is very big.


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