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codecs
https://developer.mozilla.org/en-US/docs/Web/Media/Formats/Audio_concepts
audio is represented by a stream of samples, each specifying the amplitude of the audio waveform as measured for a given slice of the overall waveform of the audio signal
Higher the amplitude (height) of the wave, the louder the sound is at that instant. The lower the frequency, the fewer the oscillations. High frequencies produce more oscillations. The units of frequency are called hertz (Hz). Humans with normal hearing can hear sounds between 20 Hz and 20,000 Hz. Frequencies above 20,000 Hz are known as ultrasound
sample rate number of samples taken per second.The more samples you take, the smoother the wave becomes.
sample size The size of an individual sample. Mostly 16 bit signed integers.
channel count number of channels contained in the audio signal. In stereo sound, there are two audio sources: one speaker on the left, and one on the right.
Each of these is represented by one channel.
two types of audio channel(standard and LFE-Low frequency Enhancement)
Monophonic audio has one channel, stereo sound has two channels, 5.1 surround sound has 6 channels (five standard and one LFE)
- (8 kHz). This is enough for human speech to be comprehensible.
- (44.1 Khz) CDs provide uncompressed 16-bit stereo sound at 44.1 kHz.
- (48 kHz. This is used for computer audio and DVD
- (96 kHz) High resolution audio
- (192 kHz) Ultra-high resolution
44.1 kHz is considered the minimum "high fidelity" sampling rate based on Nyquist shannon sampling theorem.
High-resolution (96 kHz) and ultra-high resolution (192 kHz) audio are useful for audio mastering, where you need as much quality as possible while manipulating and editing the sound before downsampling to the sample rate you will use for the final product.
A coder or encoder encodes a data stream or a signal for transmission or storage, possibly in encrypted form, and the decoder function reverses the encoding for playback or editing.
lossy data compresion discrete cosine transform (DCT), used in compression standards such as JPEG images, H.26x and MPEG video, and MP3 and AAC audio.
Audio codecs for cell phones need to have very low latency between source encoding and playback.
In contrast, for recording or broadcasting can use high-latency audio compression techniques to achieve higher fidelity at a lower bit rate.
format of audio and video media files is defined in two/three parts, audio and/or video codec used and container(metadata) format
Popular : Ogg, ASF, QuickTime, RealMedia, Matroska, and DivX Media Format
ISO Standardized: MPEG transport stream, MPEG program stream, MP4, and ISO base media file format.
Other : AVI
https://developer.mozilla.org/en-US/docs/Web/Media/Formats/Video_codecs
Encoded or compressed audio is used on the web.