![]() ![]() įLAC is optimized for decoding speed at the expense of encoding speed. The meaning of each compression level varies by implementation. The levels are labeled from 0 to 8, with higher numbers resulting in a higher compression ratio, at the cost of compression speed. Regardless of the amount of compression, the original data can always be reconstructed perfectly.įor user's convenience, the reference implementation defines 9 compression levels, which are presets of the more technical parameters to the encoding algorithm. The amount of compression is determined by various parameters, including the order of the linear prediction model and the block size. Įven though the reference encoder uses a single block size for the whole stream, FLAC allows the block size in samples to vary per block. In place of a mid channel, the left channel or the right channel may be encoded instead, which is sometimes more space-efficient. The channels are transformed into a side channel, which is the difference between the two input channels, and a mid channel, the sum of the two input channels. As FLAC compresses losslessly, the decoded waveform is identical to the waveform before encoding.įor two-channel stereo, the encoder may choose to joint-encode the audio. The result is formed by adding the residual and the calculated waveform. The description of the mathematical approximation is then used to calculate a waveform. The compressed residual is first decoded. The decoding process is the reverse of encoding. In many cases, a description of the approximation and the encoded residual takes up less space than using pulse-code modulation. Finally, the difference between the approximation and the input, called residual, is encoded using Rice coding. A description of the approximation, which is only a few bytes in length, is then written. The encoder then tries to find a good mathematical approximation of the block, either by fitting a simple polynomial, or through general linear predictive coding. If the audio contains multiple channels, each channel is encoded separately as a subblock. In the first stage, the input audio is split into blocks. The FLAC encoding algorithm consists of multiple stages. FLAC uses Vorbis comments for textual metadata like track title and artist name. It may also contain other information, the album cover for example. Properties like the sample rate and the number of channels are always contained in the metadata. The data block contains the audio information. The rest of the header contains the number of samples, position of the frame, channel assignment, and optionally the sample rate and bit depth. A frame header begins with a sync word, used to identify the beginning of a valid frame. Each frame is encoded independent of each other. The encoded audio is divided into frames, which consists of a header, a data block, and a CRC16 checksum. File structure Ī FLAC file consists of the magic number fLaC, metadata, and encoded audio. Design įLAC is a lossless encoding of linear pulse-code modulation data. In 2019, FLAC was proposed as an IETF standard. ![]() Version 1.3.0 was released on, at which point development was moved to the git repository. is home to other free compression formats such as Vorbis, Theora, Speex and Opus. On 29 January 2003, the Xiph.Org Foundation and the FLAC project announced the incorporation of FLAC under the banner. Version 1.0 was released on 20 July 2001. The bitstream format was frozen when FLAC entered beta stage with the release of version 0.5 of the reference implementation on 15 January 2001. FLAC has support for metadata tagging, album cover art, and fast seeking.ĭevelopment was started in 2000 by Josh Coalson. Digital audio compressed by FLAC's algorithm can typically be reduced to between 50 and 70 percent of its original size and decompresses to an identical copy of the original audio data.įLAC is an open format with royalty-free licensing and a reference implementation which is free software. FLAC ( / f l æ k/ Free Lossless Audio Codec) is an audio coding format for lossless compression of digital audio, developed by the Xiph.Org Foundation, and is also the name of the free software project producing the FLAC tools, the reference software package that includes a codec implementation. ![]()
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