MP3 - Revision history

Maikmerten: /* Encoders/decoders (supported platforms) */ "Helix MP3" to "Helix MP3 Encoder" to differentiate from the Helix MP3 Decoder (which also exists)

2024-03-25T09:42:57Z

Encoders/decoders (supported platforms): "Helix MP3" to "Helix MP3 Encoder" to differentiate from the Helix MP3 Decoder (which also exists)

← Older revision		Revision as of 09:42, 25 March 2024
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	=== Encoders/decoders (supported platforms) ===		=== Encoders/decoders (supported platforms) ===
	* [[LAME]] (Win32/Posix)		* [[LAME]] (Win32/Posix)
	* [[Helix MP3]] (Win32/Posix)		* [[Helix MP3 Encoder]] (Win32/Posix)
	* [[Audioactive]] (Win32)		* [[Audioactive]] (Win32)
	* [[Blade]] (Win32/Posix)		* [[Blade]] (Win32/Posix)

Maikmerten: /* Encoders/decoders (supported platforms) */ add Helix MP3

2024-03-25T09:41:45Z

Encoders/decoders (supported platforms): add Helix MP3

← Older revision		Revision as of 09:41, 25 March 2024
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	=== Encoders/decoders (supported platforms) ===		=== Encoders/decoders (supported platforms) ===
	* [[LAME]] (Win32/Posix)		* [[LAME]] (Win32/Posix)
			* [[Helix MP3]] (Win32/Posix)
	* [[Audioactive]] (Win32)		* [[Audioactive]] (Win32)
	* [[Blade]] (Win32/Posix)		* [[Blade]] (Win32/Posix)

12.218.147.66: /* Pros */ Patents have expired. There is no more licensing program.

2020-06-06T05:23:08Z

Pros: Patents have expired. There is no more licensing program.

← Older revision		Revision as of 05:23, 6 June 2020
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	* Fast decoding, lower complexity than [[Advanced Audio Coding\|AAC]] or [[Vorbis]]		* Fast decoding, lower complexity than [[Advanced Audio Coding\|AAC]] or [[Vorbis]]
	* Anyone can create their own implementation (Specs and demo sources available)		* Anyone can create their own implementation (Specs and demo sources available)
	* ~~Relaxed licensing schedule~~		* Since the patents have expired, MP3 is in the public domain.

	=== Cons ===		=== Cons ===

82.231.158.103: /* LAME tag */

2019-11-14T01:55:36Z

LAME tag

← Older revision		Revision as of 01:55, 14 November 2019
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	* separate delay & padding values for gapless playback		* separate delay & padding values for gapless playback
	* various encoder settings (expanded in LAME 3.94 to include presets)		* various encoder settings (expanded in LAME 3.94 to include presets)
	The modified header is also included in CBR files (effective LAME 3.94), with "Info" instead of "~~XING~~" near the beginning.		The modified header is also included in CBR files (effective LAME 3.94), with "Info" instead of "Xing" near the beginning.

	====Specs====		====Specs====

Dynamic: /* Model 2 technical details */ Replaced mentions of BM with Basilar Membrane - please edit if incorrect

2013-01-29T15:46:33Z

Model 2 technical details: Replaced mentions of BM with Basilar Membrane - please edit if incorrect

← Older revision		Revision as of 15:46, 29 January 2013
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	;3. Grouping of spectral values into threshold calculation partitions.		;3. Grouping of spectral values into threshold calculation partitions.

	The uniform [[frequency]] decomposition and poor selectivity of the filterbank do not reflect the response of the BM. To accurately model the masking phenomenon characteristic of the BM, the spectral values are grouped into a large number of partitions. The exact number of threshold partitions depends on the choice of sampling rate. This transformation provides a resolution of approximately either 1 FFT line or 1/3 critical band, whichever is smaller. At low frequencies, a single line of the FFT will constitute a partition, while at high frequency\|frequencies many lines are grouped into one.		The uniform [[frequency]] decomposition and poor selectivity of the filterbank do not reflect the response of the ear's Basilar Membrane. To accurately model the masking phenomenon characteristic of the Basilar Membrane, the spectral values are grouped into a large number of partitions. The exact number of threshold partitions depends on the choice of sampling rate. This transformation provides a resolution of approximately either 1 FFT line or 1/3 critical band, whichever is smaller. At low frequencies, a single line of the FFT will constitute a partition, while at high frequency\|frequencies many lines are grouped into one.

	;4. Estimation of tonality indices.		;4. Estimation of tonality indices.
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	It is necessary to identify tonal and non-tonal (noise-like) components because the masking abilities of the two types of signals differ. Model 2 does not explicitly separate tonal and non-tonal components. Instead, it computes a tonality index as a function of frequency. This is an indicator of the tone-like or noise-like nature of the spectral component. The tonality index is based on a measure of predictability. Linear extrapolation is used to predict the component values of the current window from the previous two analysis windows. Model 2 uses this index to interpolate between pure tone-masking-noise and noise-masking-tone values. Tonal components are more predictable and thus have a higher tonality index. As this process has memory, it is more likely to discriminate better between tonal and non-tonal components, unlike psychoacoustic Model 116.		It is necessary to identify tonal and non-tonal (noise-like) components because the masking abilities of the two types of signals differ. Model 2 does not explicitly separate tonal and non-tonal components. Instead, it computes a tonality index as a function of frequency. This is an indicator of the tone-like or noise-like nature of the spectral component. The tonality index is based on a measure of predictability. Linear extrapolation is used to predict the component values of the current window from the previous two analysis windows. Model 2 uses this index to interpolate between pure tone-masking-noise and noise-masking-tone values. Tonal components are more predictable and thus have a higher tonality index. As this process has memory, it is more likely to discriminate better between tonal and non-tonal components, unlike psychoacoustic Model 116.

	;5. Simulation of the spread of masking on the BM.		;5. Simulation of the spread of masking on the Basilar Membrane.

	A strong signal component affects the audibility of weaker components in the same critical band and the adjacent bands. Model 2 simulates this phenomenon by applying a Spreading function to spread the energy of any critical band into its surrounding bands. On the [[Bark]] scale, the spreading function has a constant shape as a function of partition number, with slopes of +25 and –10 dB per Bark.		A strong signal component affects the audibility of weaker components in the same critical band and the adjacent bands. Model 2 simulates this phenomenon by applying a Spreading function to spread the energy of any critical band into its surrounding bands. On the [[Bark]] scale, the spreading function has a constant shape as a function of partition number, with slopes of +25 and –10 dB per Bark.

Mjb: /* Gapless playback info */ minor phrasing adjustment to previous edit

2013-01-21T05:11:27Z

Gapless playback info: minor phrasing adjustment to previous edit

← Older revision		Revision as of 05:11, 21 January 2013
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	====Gapless playback info====		====Gapless playback info====
	In addition to the seek-point table, the Fraunhofer format contains a combined encoder delay & padding value (measured in samples), which can assist [[gapless playback]]. The encoder delay value is the number of samples added to the beginning of the audio data, and the encoder padding value is the number of samples added to the end. There's also a decoder delay, usually 529 samples of junk samples added to the beginning by the decoder. To determine the starting and ending samples ~~for trimming~~ delay ~~and~~ padding ~~from~~ the decoder output, MP3 players can perform the following calculation:		In addition to the seek-point table, the Fraunhofer format contains a combined encoder delay & padding value (measured in samples), which can assist [[gapless playback]]. The encoder delay value is the number of samples added to the beginning of the audio data, and the encoder padding value is the number of samples added to the end. There's also a decoder delay, usually 529 samples of junk samples added to the beginning by the decoder. To determine the starting and ending samples of the non-delay, non-padding portion of the decoder output, MP3 players can perform the following calculation:

	<nowiki>		<nowiki>

Mjb: /* VBRI, XING, and LAME headers */ more precise info about seek table. corrected a few things. can't assume delay & padding are silent, or that there's always enough padding. formatting, headings.

2013-01-21T05:09:52Z

VBRI, XING, and LAME headers: more precise info about seek table. corrected a few things. can't assume delay & padding are silent, or that there's always enough padding. formatting, headings.

← Older revision		Revision as of 05:09, 21 January 2013
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	Xing and Fraunhofer each developed their own formats for this header. The Xing-format header is just called the ''Xing header'' or ''XING header''. The Fraunhofer-format header is called the ''VBRI header'' or ''VBR Info header''.		Xing and Fraunhofer each developed their own formats for this header. The Xing-format header is just called the ''Xing header'' or ''XING header''. The Fraunhofer-format header is called the ''VBRI header'' or ''VBR Info header''.

	Both formats specify a table of seek points which help players ~~jump to approximate points in the file~~. ~~In addition to the seek-point table~~, ~~the Fraunhofer format contains a combined encoder delay & padding value (measured~~ in ~~samples), which can assist [[gapless playback]]. The encoder delay value is the number of null samples added to the beginning~~, ~~the encoder padding one is the number of samples added to the end of the audio data. In addition, there is the notion of~~ a ~~decoder delay, which is 529 samples~~ in ~~all known MP3s~~. ~~To get the gapless range of samples of the decoded data, perform the following calculation:~~		====Seek table====
			Both formats specify a table of seek points, which help players correlate playback position (e.g., in seconds, or as a percentage) with byte offsets in the file.

	~~gapless_range_start~~ = ~~encoder_delay + decoder_delay~~		====Gapless playback info====
	~~gapless_range_end = num_frames * samples_per_frame~~ - ~~encoder_padding + decoder_delay~~		In addition to the seek-point table, the Fraunhofer format contains a combined encoder delay & padding value (measured in samples), which can assist [[gapless playback]]. The encoder delay value is the number of samples added to the beginning of the audio data, and the encoder padding value is the number of samples added to the end. There's also a decoder delay, usually 529 samples of junk samples added to the beginning by the decoder. To determine the starting and ending samples for trimming delay and padding from the decoder output, MP3 players can perform the following calculation:

			<nowiki>
			gapless_range_start = encoder_delay + decoder_delay
			if encoder_padding < decoder_delay:
			gapless_range_end = total_samples
			else:
			gapless_range_end = total_samples - encoder_padding + decoder_delay</nowiki>

			Alternatively, when <code>encoder_padding</code> < <code>decoder_delay</code>, a player could feed an extra MP3 frame to the decoder (e.g. a silent frame, or the first frame of the next MP3 in a sequence), and then use the second <code>gapless_range_end</code> calculation. At least one player (Rockbox) does the latter to handle an uncommon type of MP3 encoded specially for gapless playback, where one long stream is split up and written into separate files.

			====LAME tag====
	The [[LAME]] encoder extends the Xing header format. This modified header is sometimes called a ''LAME header'' or ''LAME tag'', although the actual LAME tag is only the LAME-specific data embedded in unused space in the header.		The [[LAME]] encoder extends the Xing header format. This modified header is sometimes called a ''LAME header'' or ''LAME tag'', although the actual LAME tag is only the LAME-specific data embedded in unused space in the header.

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	The modified header is also included in CBR files (effective LAME 3.94), with "Info" instead of "XING" near the beginning.		The modified header is also included in CBR files (effective LAME 3.94), with "Info" instead of "XING" near the beginning.

			====Specs====
	The Fraunhofer VBRI header and the LAME tag have explicit specifications. The Xing format can only be inferred from the C code the company provided to read the headers. Here are links to the code and specs:		The Fraunhofer VBRI header and the LAME tag have explicit specifications. The Xing format can only be inferred from the C code the company provided to read the headers. Here are links to the code and specs:
	* [http://gabriel.mp3-tech.org/mp3infotag.html LAME MP3 Info Tag spec]		* [http://gabriel.mp3-tech.org/mp3infotag.html LAME MP3 Info Tag spec]

Mjb: /* VBRI, XING, and LAME headers */ FhG moved stuff around again, but also made available the real VBRI header spec

2013-01-21T03:19:41Z

VBRI, XING, and LAME headers: FhG moved stuff around again, but also made available the real VBRI header spec

← Older revision		Revision as of 03:19, 21 January 2013
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	The modified header is also included in CBR files (effective LAME 3.94), with "Info" instead of "XING" near the beginning.		The modified header is also included in CBR files (effective LAME 3.94), with "Info" instead of "XING" near the beginning.

	The LAME tag ~~has an~~ explicit ~~specification, but the~~ Xing ~~and Fraunhofer formats~~ can only be inferred from the C code the ~~companies~~ provided to read the headers:		The Fraunhofer VBRI header and the LAME tag have explicit specifications. The Xing format can only be inferred from the C code the company provided to read the headers. Here are links to the code and specs:
	* [http://gabriel.mp3-tech.org/mp3infotag.html LAME MP3 Info Tag spec]		* [http://gabriel.mp3-tech.org/mp3infotag.html LAME MP3 Info Tag spec]
	* [http://www.~~iis~~.~~fraunhofer.de~~/bf/~~amm/download/MP3%20VBR~~-~~Header%20Software%20Development%20Kit~~.~~zip~~ Fraunhofer MP3 VBR-Header SDK]		* [http://www.all4mp3.com/tools/tech-and-tools.php All4mp3 mp3 Tech & Tools downloads] - official distribution site for Fraunhofer's ''Source code to add VBRi header to mp3 file'' (contains header spec) and ''MP3 VBR-Header SDK'' (header-reading C code sample)
	* [http://www.mp3-tech.org/programmer/sources/vbrheadersdk.zip Xing Variable Bitrate MP3 Playback SDK]		* [http://www.mp3-tech.org/programmer/sources/vbrheadersdk.zip Xing Variable Bitrate MP3 Playback SDK]
	* [http://mp3decoders.mp3-tech.org/decoders_lame.html#delays Information about common encoder and decoder delays]		* [http://mp3decoders.mp3-tech.org/decoders_lame.html#delays Information about common encoder and decoder delays]

Mjb: /* VBRI, XING, and LAME headers */ correction to previous edit

2013-01-20T13:58:51Z

VBRI, XING, and LAME headers: correction to previous edit

← Older revision		Revision as of 13:58, 20 January 2013
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	* separate delay & padding values for gapless playback		* separate delay & padding values for gapless playback
	* various encoder settings (expanded in LAME 3.94 to include presets)		* various encoder settings (expanded in LAME 3.94 to include presets)
	The modified header is also included in CBR files (effective LAME 3.94), with "~~INFO~~" ~~(Fraunhofer-style)~~ instead of "XING" near the beginning.		The modified header is also included in CBR files (effective LAME 3.94), with "Info" instead of "XING" near the beginning.

	The LAME tag has an explicit specification, but the Xing and Fraunhofer formats can only be inferred from the C code the companies provided to read the headers:		The LAME tag has an explicit specification, but the Xing and Fraunhofer formats can only be inferred from the C code the companies provided to read the headers:

Mjb: /* VBRI, XING, and LAME headers */ added detail about content, usage, and history of LAME tag

2013-01-20T13:31:11Z

VBRI, XING, and LAME headers: added detail about content, usage, and history of LAME tag

← Older revision		Revision as of 13:31, 20 January 2013
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	gapless_range_end = num_frames * samples_per_frame - encoder_padding + decoder_delay		gapless_range_end = num_frames * samples_per_frame - encoder_padding + decoder_delay

	The [[LAME]] encoder ~~further extended~~ the Xing format ~~to work for CBR and to include encoder settings and separate delay & padding values~~. This ~~version of the Xing~~ header is ~~often~~ called a ''LAME header'' or ''LAME tag'', although ~~according to the spec,~~ the actual LAME tag is only the ~~portion that's different from~~ a ~~normal Xing~~ header. It has an explicit specification, but the Xing and Fraunhofer formats can only be inferred from the C code the companies provided to read the headers:		The [[LAME]] encoder extends the Xing header format. This modified header is sometimes called a ''LAME header'' or ''LAME tag'', although the actual LAME tag is only the LAME-specific data embedded in unused space in the header.

			When the header was first added in LAME 3.12, the LAME tag contained only a 20-byte LAME version string. In LAME 3.90, this region was expanded to hold additional data, such as:
			* audio and info tag CRCs
			* separate delay & padding values for gapless playback
			* various encoder settings (expanded in LAME 3.94 to include presets)
			The modified header is also included in CBR files (effective LAME 3.94), with "INFO" (Fraunhofer-style) instead of "XING" near the beginning.

			The LAME tag has an explicit specification, but the Xing and Fraunhofer formats can only be inferred from the C code the companies provided to read the headers:
	* [http://gabriel.mp3-tech.org/mp3infotag.html LAME MP3 Info Tag spec]		* [http://gabriel.mp3-tech.org/mp3infotag.html LAME MP3 Info Tag spec]
	* [http://www.iis.fraunhofer.de/bf/amm/download/MP3%20VBR-Header%20Software%20Development%20Kit.zip Fraunhofer MP3 VBR-Header SDK]		* [http://www.iis.fraunhofer.de/bf/amm/download/MP3%20VBR-Header%20Software%20Development%20Kit.zip Fraunhofer MP3 VBR-Header SDK]