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What is an audio format ?
An audio file format is a file format for storing audio data
on a computersystem.
The data can then be stored uncompressed,
orcompressed to reduce the file size.
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3 major groups of audio file formats:
Uncompressed audio formats
Lossless data compression
Lossy compression
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Uncompressed audio formats
There is one major uncompressed audioformat, PCM .
Pulse-code modulation is
a digital representation of an
analog signal where the magnitude of the
signal is sampled regularly at uniform intervals
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PCM stored as
.WAVOn Windows
.AIFFOn Mac OS
.CDAAudio CD
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Examples
wav standard audio file container formatused mainly in Window PCs.
Aiff the standard audio file format used by
Apple. It is like a wav file for the Mac raw a raw file can contain audio in any codec
but is usually used with PCM audio data.
au the standard audio file format usedby Sun, Unix and Java
Large in sizearound 10 MB per
minute.
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Lossless data compression:
It allows the exact original data to bereconstructed from the compressed data.
For example, it is used in the popular ZIP file
format Lossless compression is used in cases where it
is important that the original and the
decompressed data be identical
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Examples
flac- a lossless compression codec. If you compress a
PCM file to flac and then restore it again it will be a
perfect copy of the original.
Apple Lossless Windows Media Audio Lossless (WMA Lossless)
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Lossy compression:
Lossy compression is a datacompression method which discards (loses)
some of the data, in order to achieve its goal,
with the result that decompressing the datayields content that is different from the
original, though similar enough to be useful in
some way.
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Examples
mp3- By eliminating portions of the audio file that areessentially inaudible, mp3 files are compressed toroughly one-tenth the size of an equivalent PCM filewhile maintaining good audio quality.
wma - the popular Windows Media Audio format owned by
Microsoft.
aac- the Advanced Audio Coding format is based on the
MPEG4 audio standard owned by Dolby.
atrac (.wav) - It always has a .wav file extension.
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Common formats and their description:
The WAV format WAV files tend to be very large, since
they are not compressed at all. WAVs are used where space is not a huge issue, or where
compression is not possible for other reasons standardcompact discs, for example, use an uncompressed digitalaudio file using pulse-code modulation (PCM).
The MP3 format MP3 files are ideal for sharing online, orin any context where space is at a premium, because theycan be compressed down to much smaller sizes than WAV
formats. The quality is reduced most MP3s are encoded at
anywhere between 160 and 320 kb/s, as opposed to the1411.2 kb/s of a WAV file but for many people the lossof sound fidelity is unnoticeable, especially with cheaper
speakers.
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AAC It is a newer compression system, and isgenerally agreed upon as having a higher-
quality sound at the same compression levelsas MP3.
Windows Media Audio (.wma)Windows Media Audio (.wma) was developed
to compete with the MP3 format for WindowsMedia Player. Microsoft claims that the WMAfiles are compressed three times more thanMP3s yet retain their original sound quality.
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MP3 VS AAC
It's advantage is that AAC files are of smaller
size but of comparatively good.
128kbps mp3 = 96kbps AAC without little
noticeable loss of quality, and the file will be
600kb ~ 750kb smaller in size. If you convert
192kbps mp3 to AAC the target file will be of
96kbps with tiny loss of sound quality, butHALF of the mp3 file size.
Is aac better ?
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Ring tone encoding formats
AAC: Some phones like the SonyEricsson W810i support ring tones in ".m4a" AAC
format. The iPhone supports ring tones in ".m4r"
AAC format.
AMR: Audio compression format specialized in
speech used by Nokia before mp3 became standard.
MID / MIDI: Popular sound format.
eMelody: Older monophonic Ericsson format.
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In telecommunications and computing, bitrateis the number ofbits that are conveyed or
processed per unit of time.
How does bit rate effect file size ?For a 128kbps MP3/AAC file, each second of audiorequires 128kilobits of data. We are talking about kiloBITShere, not kilobytes (there are 8 bits in a byte).
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Relation b/w size of file and bit rate x = length of song (in seconds)
y = bitrate (in kilobits per second)z = resultant file size (in kilobytes)
z = (x * y) / 8
Example
So if you have a 5 minute song, encoding at 128kbps, you woulddo this as follows:
5 minutes = 300 seconds128kbps * 300 seconds = 38,400 kilobits of data38,400 kilobits / 8 = 4,800 kb
To take this one step further, you can convert this intoMegabytes by dividing by 1,024, so 4800/1024 = 4.6875Mb
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List of audio formats Wav: standard audio file container format used mainly in Windows PCs. Ogg:-- a free, open source container format supporting a variety of codecs Mpc: -- Musepack or MPC (formerly known as MPEGplus
Flac:--Free Lossless Audio Codec Aiff:-- the standard audio file format used by Apple Raw:-- a raw file can contain audio in any codec but is usually used with PCM audio data Au:-- the standard audio file format used by Sun, Unix and Java
mp3- the MPEG Layer-3 format is the most popular format for downloading and storingmusic.
gsm- designed for telephony use in Europe, gsm is a very practical format for telephone
quality voice. dct- A variable codec format designed for dictation. wma- the popular Windows Media Audio format owned by Microsoft aac- the Advanced Audio Coding format is based on the MPEG4 audio standard owned
by Dolby. atrac (.wav)- the older style Sony ATRAC format ra- a Real Audio format designed for streaming audio over the Internet ram- a text file that contains a link to the Internet address where the Real Audio file is
stored dss- Digital Speech Standard files are an Olympus proprietary format. msv- a Sony proprietary format for Memory Stick compressed voice files dvf- a Sony proprietary format for compressed voice files; commonly used by Sony
dictation recorders.
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mp3- the MPEG Layer-3 format is the most popular format for downloading andstoring music.
gsm- designed for telephony use in Europe, gsm is a very practical format fortelephone quality voice.
dct- A variable codec format designed for dictation.
wma- the popular Windows Media Audio format owned by Microsoft
aac- the Advanced Audio Coding format is based on the MPEG4 audio standardowned by Dolby.
atrac (.wav)- the older style Sony ATRAC format
ra- a Real Audio format designed for streaming audio over the Internet
ram- a text file that contains a link to the Internet address where the Real Audio fileis stored
dss- Digital Speech Standard files are an Olympus proprietary format.
msv- a Sony proprietary format for Memory Stick compressed voice files
dvf- a Sony proprietary format for compressed voice files; commonly used by Sonydictation recorders.
KWS: Kyocera's ringer format Morse code: Text files with a .MORSE extension get converted into morse code
songs
MOT: An older ringer format for Motorola phones.
Nokia / SCKL / OTT: Nokia Smart Messaging format
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PDB: Palm database. This is the format used to load ring tones on PDAphones
PMD: Format co-created by Qualcomm and Japanese company Faith
QCP: File format generated by Qualcomm PureVoice software. RTTTL: A popular text format for ring tones
RTX: Similar to RTTTL with some advanced features. Also the octaves aredifferent on RTX.
Samsung1 & Samsung2: Samsung keypress format
Siemens Keypress: Can create and read in a Siemens text file format Siemens SEO: Siemens SEO binary format
SMAF: Yamaha music format that combines MIDI with instrument sound data(aka Module files)
SRT: Sipura ringtone for Sipura Technology VoIP phones
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Video FormatsAVI:- Audio Video Interleaved, is developed
by Microsoft in 1992
Advantages
High image quality
Application in multi-platforms
Disadvantages
Large volume
higher-version Windows Media Player simplycant play AVI videos which are edited with earlier
codes, and vise versa
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MPEG, Moving Picture Expert Group
Is the format of VCD, SVCD, DVD
This format applies lossy compression to reduce redundant info in
active images, and to express it more clearly
MPEG makes use of the fact that the two contiguous images are
almost the same
MOV, developed by Apple
features a high compression ratio and near perfect definition
most outstanding trait is its trans-platform ability, supporting
Windows other than its intimate pal MacOS.
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ASF
Is an extensible file format designed primarily
for storing and playing synchronized digital
media stream.
ASF is the container format for Windows
Media Audio and Windows Media Video-
based content. (WMA,WMV)
WMA
WMV
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Mobile video formats
3GPP (.3gp)
It was developed by the 3rd GenerationPartnership Project, hence the name 3GPP.
Flash Lite Flash Lite is a streamlined version of Flash that
was developed specifically for mobile phonesand portable devices.
The full version of Flash of course is the singlemost common online video file format.
It is designated by an .FLV file extension
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MPEG-4
Is a good sharing format for mobile video
Also commonly used for online video in general but isone of the smaller formats so it works well for mobilevideo too.
MP4
Defines the storage of MPEG-4 audio, scenes andmultimedia.
The entire scene is described by an initial objectdescriptor (IOD). This is stored in a special box withinthe movie atom in MP4 files.
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The latest
H.264 Coding Format
Also known as MPEG-4 Part 10 or AVC (for
Advanced Video Coding).
Provide good video quality at substantially
lower bit rates than previous standards.
Provides quarter-pixel precision for motion
compensation enables very precise description
of the displacements of moving areas.
More attractive for video network delivery and
for delivery of HD, high definition video