Gapless playback - Revision history

89.72.105.169: https://hydrogenaud.io/index.php/topic,104585.0.html

2016-11-21T20:39:39Z

https://hydrogenaud.io/index.php/topic,104585.0.html

← Older revision		Revision as of 20:39, 21 November 2016
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	* (Ogg) [[Vorbis]]		* (Ogg) [[Vorbis]]
			* [[Opus]]
	* [[Speex]]		* [[Speex]]

Mjb: /* How to add or repair gap metadata in MP3s */

2015-01-12T04:29:51Z

How to add or repair gap metadata in MP3s

← Older revision		Revision as of 04:29, 12 January 2015
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	# Determine the encoder delay (number of silent samples at the beginning of each track). This number should be identical for all tracks if they were encoded with the same software. For example, for tracks encoded with [[Gogo]], since it's [[LAME]]-based, the delay should be 576 samples, but it wouldn't hurt to check visually in the editor.		# Determine the encoder delay (number of silent samples at the beginning of each track). This number should be identical for all tracks if they were encoded with the same software. For example, for tracks encoded with [[Gogo]], since it's [[LAME]]-based, the delay should be 576 samples, but it wouldn't hurt to check visually in the editor.
	# For each track that should end with gapless transition, determine the number of silent samples at the end (the padding). Unfortunately this procedure can not be reliably automated, because silent samples may not strictly equal zero (due to the encoder filter ringing). You'll need to visually search for the waveform cut-off, which probably won't be abrupt.		# For each track that should end with gapless transition, determine the number of silent samples at the end (the padding). Unfortunately this procedure can not be reliably automated, because silent samples may not strictly equal zero (due to the encoder filter ringing). You'll need to visually search for the waveform cut-off, which probably won't be abrupt.
	# Determine the true length of the track in samples: true length = (raw length) - (encoder delay) - (padding). ~~This~~ number should be a multiple of 588 (the audio CD sector size). If it is not, then either you incorrectly determined number of padding samples, or the content was not encoded from ~~the~~ audio CD, or possibly it was digitally processed prior to mp3 encoding.		# Determine the true length of the track in samples: true length = (raw length) - (encoder delay) - (padding). If the track came from an audio CD, then this number should be a multiple of 588 (the audio CD sector size). If it is not, then either you incorrectly determined the number of padding samples, or the content was not encoded from an audio CD, or possibly it was digitally processed prior to mp3 encoding.
	# Edit the mp3 info frame with foobar2000 (local menu -> utilities -> edit mp3 gapless playback information). Enter the encoder delay from step 2 into the "encoder delay" field and the true track length from step 4 into the "padding" field. Save the changes.		# Edit the mp3 info frame with foobar2000 (local menu -> utilities -> edit mp3 gapless playback information). Enter the encoder delay from step 2 into the "encoder delay" field and the true track length from step 4 into the "padding" field. Save the changes.

92.23.163.8: /* Test samples */ fixed download link to gapless_WAVPACK_free_of_right.zip

2014-04-08T22:10:18Z

Test samples: fixed download link to gapless_WAVPACK_free_of_right.zip

← Older revision		Revision as of 22:10, 8 April 2014
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	== Test samples ==		== Test samples ==
	* [http://~~guruboolez~~.~~free.fr/samples~~/~~gapless~~/gapless_WAVPACK_free_of_right.zip]: 17 very short gapless samples (2 MB)		* [http://tiffman.com/gtkpod/gapless_WAVPACK_free_of_right.zip]: 17 very short gapless samples (2 MB)

	== External links ==		== External links ==

71.106.67.83: /* Compression scheme artifacts */ m gm

2013-03-17T07:57:27Z

Compression scheme artifacts: m gm

← Older revision		Revision as of 07:57, 17 March 2013
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	=== Compression scheme artifacts ===		=== Compression scheme artifacts ===
	Most lossy audio compression schemes add a small amount of silence both ends of the audio. Due to the introduction of such gaps, the duration of the output is slightly increased. Silence at the beginning is called '''delay''' and silence at the end is '''padding'''. Delay can be called '''encoder delay''' or '''decoder delay''' depending on what part of the compression scheme introduces the delay. Padding normally is only added by the encoder. [[#Common encoder delay values\|Common encoder delay values]] are in a table below.		Most lossy audio compression schemes add a small amount of silence to both ends of the audio. Due to the introduction of such gaps, the duration of the output is slightly increased. Silence at the beginning is called '''delay''' and silence at the end is '''padding'''. Delay can be called '''encoder delay''' or '''decoder delay''' depending on what part of the compression scheme introduces the delay. Padding normally is only added by the encoder. [[#Common encoder delay values\|Common encoder delay values]] are in a table below.

	Many compression schemes involve a time/frequency domain transform (such as an [[MDCT]]) which unavoidably introduces a certain amount of silence (part of the encoder delay) at the beginning of the stream. This gap can be enlarged at decode time when a reverse-MDCT is performed, because the reverse transform will also introduce a gap (decoder delay) of its own.		Many compression schemes involve a time/frequency domain transform (such as an [[MDCT]]) which unavoidably introduces a certain amount of silence (part of the encoder delay) at the beginning of the stream. This gap can be enlarged at decode time when a reverse-MDCT is performed, because the reverse transform will also introduce a gap (decoder delay) of its own.

Mjb: /* Testing for gapless */ minor copy edits

2012-07-27T07:48:14Z

Testing for gapless: minor copy edits

← Older revision		Revision as of 07:48, 27 July 2012
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	The best way to test for gapless playback is by using ''Test Samples'' listed at the end of this page.		The best way to test for gapless playback is by using ''Test Samples'' listed at the end of this page.

	~~Some people attempts~~ to ~~detect~~ gapless by generating pure tones, and encoding them into a lossy format. This is not recommended for two reasons:		It's tempting to test gapless playback by generating tracks with pure tones, and encoding them into a lossy format. This is not recommended for two reasons:

	1. Unless the first tone ends at 0 level and the second tone starts at 0 level, a glitch will be heard during transition.		# Unless the first tone ends at 0 level and the second tone starts at 0 level, a glitch will be heard during transition.
	2. Some decoders chop off the end and/or the start of the audio data. So the playback will be perceived as gapless, while it is actually not.		# Some decoders chop off the end and/or the start of the audio data. So the playback will be perceived as gapless, while it is actually not.

	See the discussion on [http://www.hydrogenaudio.org/forums/index.php?showtopic=40995&st=0&p=360548&#entry360548 this HA thread].		See the discussion on [http://www.hydrogenaudio.org/forums/index.php?showtopic=40995&st=0&p=360548&#entry360548 this HA thread].

Mjb: + a link to a post about what iTunes does

2011-02-01T00:57:36Z

+ a link to a post about what iTunes does

← Older revision		Revision as of 00:57, 1 February 2011
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	== Test samples ==		== Test samples ==
	* [http://guruboolez.free.fr/samples/gapless/gapless_WAVPACK_free_of_right.zip]: 17 very short gapless samples (2 MB)		* [http://guruboolez.free.fr/samples/gapless/gapless_WAVPACK_free_of_right.zip]: 17 very short gapless samples (2 MB)

			== External links ==
			* [http://yabb.jriver.com/interact/index.php?topic=47033.msg322589#msg322589 some info about how iTunes/QuickTime writes and handles gapless playback info]


	[[Category:Technical]]		[[Category:Technical]]

Mjb: /* How to add or repair gap metadata in MP3s */ waveform cutoff isn't always easy to spot, in my experience

2010-10-31T22:47:34Z

How to add or repair gap metadata in MP3s: waveform cutoff isn't always easy to spot, in my experience

← Older revision		Revision as of 22:47, 31 October 2010
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	# Decode all files to uncompressed wav format with foobar2000 (this is important, because if you open the mp3 directly with the wave editor its internal decoder may add extra silence at the beginning and/or at the end). You need to convert separate tracks to separate wav files, not to a single wav file.		# Decode all files to uncompressed wav format with foobar2000 (this is important, because if you open the mp3 directly with the wave editor its internal decoder may add extra silence at the beginning and/or at the end). You need to convert separate tracks to separate wav files, not to a single wav file.
	# Determine the encoder delay (number of silent samples at the beginning of each track). This number should be identical for all tracks if they were encoded with the same software. For example, for tracks encoded with [[Gogo]], since it's [[LAME]]-based, the delay should be 576 samples, but it wouldn't hurt to check visually in the editor.		# Determine the encoder delay (number of silent samples at the beginning of each track). This number should be identical for all tracks if they were encoded with the same software. For example, for tracks encoded with [[Gogo]], since it's [[LAME]]-based, the delay should be 576 samples, but it wouldn't hurt to check visually in the editor.
	# For each track that should end with gapless transition, determine the number of silent samples at the end (the padding). Unfortunately this procedure can not be reliably automated, because silent samples may not strictly equal zero (due to the encoder filter ringing). You'll need to visually search for the waveform cut-off.		# For each track that should end with gapless transition, determine the number of silent samples at the end (the padding). Unfortunately this procedure can not be reliably automated, because silent samples may not strictly equal zero (due to the encoder filter ringing). You'll need to visually search for the waveform cut-off, which probably won't be abrupt.
	# Determine the true length of the track in samples: true length = (raw length) - (encoder delay) - (padding). This number should be a multiple of 588 (the audio CD sector size). If it is not, then either you incorrectly determined number of padding samples, or the content was not encoded from the audio CD, or possibly it was digitally processed prior to mp3 encoding.		# Determine the true length of the track in samples: true length = (raw length) - (encoder delay) - (padding). This number should be a multiple of 588 (the audio CD sector size). If it is not, then either you incorrectly determined number of padding samples, or the content was not encoded from the audio CD, or possibly it was digitally processed prior to mp3 encoding.
	# Edit the mp3 info frame with foobar2000 (local menu -> utilities -> edit mp3 gapless playback information). Enter the encoder delay from step 2 into the "encoder delay" field and the true track length from step 4 into the "padding" field. Save the changes.		# Edit the mp3 info frame with foobar2000 (local menu -> utilities -> edit mp3 gapless playback information). Enter the encoder delay from step 2 into the "encoder delay" field and the true track length from step 4 into the "padding" field. Save the changes.

Mjb: Working toward having a section of best practices for producing gapless CD rips, I'm first making some clarifying additions, moves, and changes to the existing explanations of causes of gaps. Not done

2010-10-31T06:41:20Z

Working toward having a section of best practices for producing gapless CD rips, I'm first making some clarifying additions, moves, and changes to the existing explanations of causes of gaps. Not done

← Older revision		Revision as of 06:41, 31 October 2010
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	The typical situation is this:		The typical situation is this:
	# Someone uses [[DAE]] software to extract audio data from an audio CD and save it to separate files, one for each track.		# Someone uses [[DAE]] software to extract audio data from an audio CD and save it to separate files, one for each track.
	# During or after the creation of the files, the audio data is compressed with a codec like MP3.		# During or after the creation of the files, the audio data is compressed with a lossy codec like MP3.
	# Upon playback, a click or a brief (fraction-of-a-second) pause can be heard between tracks.		# Upon playback, a click or a brief (fraction-of-a-second) pause can be heard between tracks.

			Even if two lossily-compressed tracks are decompressed and merged into a single track, a gap will usually remain between them.

	== Why gaps occur ==		== Why gaps occur ==
	There are two main reasons why gaps occur during playback.		There are two main reasons why gaps occur during playback: compression scheme artifacts and poorly designed playback systems.

	=== Compression scheme artifacts ===		=== Compression scheme artifacts ===
	Most lossy audio compression schemes add a small amount of silence to the beginning of a ~~track~~. ~~One reason that this happens is because many such~~ schemes involve a time/frequency domain transform (such as an [[MDCT]]) which ~~can introduce gaps called~~ encoder delay. ~~These gaps~~ can be enlarged at decode time when a reverse-MDCT is performed, because the reverse transform will also introduce ~~gaps~~ (decoder delay) of its own. Another factor is the fact that transforms act on data in units of fixed-size blocks. In order ~~for~~ the ~~audio signal to be encoded in its entirety~~, ~~small amounts of~~ silence ~~are~~ appended to the input before the transform. If the amount ~~of padded silence is not accounted for, the padding will be decoded together with the audio data, also introducing gaps between tracks. Due~~ to ~~the introduction of such gaps~~, the ~~playtime~~ of the ~~audio data is often slightly increased~~. ~~(See [http://lame.sourceforge.net/tech-FAQ.txt LAME Technical FAQ])~~		Most lossy audio compression schemes add a small amount of silence both ends of the audio. Due to the introduction of such gaps, the duration of the output is slightly increased. Silence at the beginning is called '''delay''' and silence at the end is '''padding'''. Delay can be called '''encoder delay''' or '''decoder delay''' depending on what part of the compression scheme introduces the delay. Padding normally is only added by the encoder. [[#Common encoder delay values\|Common encoder delay values]] are in a table below.

			Many compression schemes involve a time/frequency domain transform (such as an [[MDCT]]) which unavoidably introduces a certain amount of silence (part of the encoder delay) at the beginning of the stream. This gap can be enlarged at decode time when a reverse-MDCT is performed, because the reverse transform will also introduce a gap (decoder delay) of its own.

			Another part of the encoder delay and padding is related to the overlapping nature of MDCT transforms; each segment of the encoded audio depends in part on adjacent segments. Therefore, a little bit of extra signal is required at both ends of the input in order to fully and accurately encode the frequencies found in the original ends. The encoder may add a consistent number of silent samples to one or both ends to achieve this.

			Yet another factor is the fact that transforms act on data in units of fixed-size blocks. In order to fill up the last block, silence may be appended to the input before the transform. This makes the overall padding amount hard to predict, if the length of the input isn't known.

	~~This issue is technical but also standards-related. The popular [[MP3]] standard, for example, defines no way to record~~ the amount of delay or padding for ~~later removal. Also~~, the ~~encoder delay may vary from encoder to encoder~~, ~~making automatic removal difficult. (See [http://mp3decoders.mp3-tech.org/decoders_lame.html lame v3.81 and 3.87 beta mp3 decoding quality test results] for a table~~ of ~~encoder delay values~~.~~) Even~~ if ~~two tracks are decompressed and merged into a single track~~, a gap will ~~usually remain between them. More recent compressed audio formats have been designed to address this problem, and can therefore produce gapless audio if played back correctly~~.		If the amount of encoder delay and padding are not all accurately accounted for, the encoded silence will be decoded together with the audio data, creating gaps at the ends of the track. Likewise, if the decoder delay is not accounted for, the gap at the end will be further enlarged.

	=== ~~Poor design~~ ===		This issue is technical but also standards-related. The popular [[MP3]] standard, for example, defines no way to record the amount of delay or padding for later removal. Encoder delay may vary from encoder to encoder, making automatic removal difficult. Some encoders use [[MP3#VBRI, XING, and LAME headers\|a nonstandard header]] to store actual encoder delay & padding values, but not all players/decoders support it. More recent (newer than MP3) compressed audio formats have been designed to address this problem, and can therefore produce gapless audio if played back correctly.

			=== Poorly designed playback systems ===
	Even when the audio file itself does not contain undesirable gaps, software/firmware/hardware design often adds gaps during playback. In some cases, software closes and re-opens the output stream when switching tracks, causing the hardware to create a very short "click". This problem is solved in more sophisticated designs of gapless playback.		Even when the audio file itself does not contain undesirable gaps, software/firmware/hardware design often adds gaps during playback. In some cases, software closes and re-opens the output stream when switching tracks, causing the hardware to create a very short "click". This problem is solved in more sophisticated designs of gapless playback.

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	== How to add or repair gap metadata in MP3s ==		== How to add or repair gap metadata in MP3s ==

	You will need a wave editor with a proper selection zoom feature (to count samples) and foobar2000 to edit the delay/padding info in the mp3 files.		You will need a wave editor with a proper selection zoom feature (to count samples) and foobar2000 to edit the delay/padding info in the mp3 files.

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	=== Common encoder delay values ===		=== Common encoder delay values ===
	* '''LAME''' - 576 samples		{\|class="wikitable" border=1
	* '''iTunes''' (MP3~~, not AAC) -~~ 528 samples		!encoder
	* '''FhG''' ~~(incl~~. ~~Windows Media Player)~~ - ~~672 samples~~		!delay
			\|-
			\|align="right"\|'''LAME'''
			\|align="center"\|576 samples
			\|-
			\|align="right"\|'''iTunes/QuickTime''' MP3
			\|align="center"\|528 samples
			\|-
			\|align="right"\|'''Windows Media Player/FhG FastEnc'''
			\|align="center"\|672 samples
			\|}
			Additional values for older encoders are given at [http://mp3decoders.mp3-tech.org/decoders_lame.html lame v3.81 and 3.87 beta mp3 decoding quality test results].

	==Alternative solutions==		==Alternative solutions==

Mjb: moved Gapless to Gapless playback over redirect: Seems appropriate, given the article's content

2010-10-31T04:17:31Z

moved Gapless to Gapless playback over redirect: Seems appropriate, given the article's content

← Older revision	Revision as of 04:17, 31 October 2010
(No difference)

Mjb: /* How to add or repair gap metadata in MP3s */ +common encoder delay values

2010-10-08T18:39:35Z

How to add or repair gap metadata in MP3s: +common encoder delay values

← Older revision		Revision as of 18:39, 8 October 2010
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	# Determine the true length of the track in samples: true length = (raw length) - (encoder delay) - (padding). This number should be a multiple of 588 (the audio CD sector size). If it is not, then either you incorrectly determined number of padding samples, or the content was not encoded from the audio CD, or possibly it was digitally processed prior to mp3 encoding.		# Determine the true length of the track in samples: true length = (raw length) - (encoder delay) - (padding). This number should be a multiple of 588 (the audio CD sector size). If it is not, then either you incorrectly determined number of padding samples, or the content was not encoded from the audio CD, or possibly it was digitally processed prior to mp3 encoding.
	# Edit the mp3 info frame with foobar2000 (local menu -> utilities -> edit mp3 gapless playback information). Enter the encoder delay from step 2 into the "encoder delay" field and the true track length from step 4 into the "padding" field. Save the changes.		# Edit the mp3 info frame with foobar2000 (local menu -> utilities -> edit mp3 gapless playback information). Enter the encoder delay from step 2 into the "encoder delay" field and the true track length from step 4 into the "padding" field. Save the changes.

			=== Common encoder delay values ===
			* '''LAME''' - 576 samples
			* '''iTunes''' (MP3, not AAC) - 528 samples
			* '''FhG''' (incl. Windows Media Player) - 672 samples

	==Alternative solutions==		==Alternative solutions==