Bit reservoir - Revision history

Dynamic: Rewritten example in bits per frame and kbps equivalent to avoid mixing bits per 'moment' and kilobits per second as if they were the same.

2012-07-10T18:36:48Z

Rewritten example in bits per frame and kbps equivalent to avoid mixing bits per 'moment' and kilobits per second as if they were the same.

← Older revision		Revision as of 18:36, 10 July 2012
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	The term '''bit reservoir''' is used exclusively in the [[MP3]] specification.		The term '''bit reservoir''' is used exclusively in the [[MP3]] specification.

	[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that bitrate is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen bitrate; they need a higher [[bitrate]] than the defined one. Therefore, the MP3 spec defines a bit reservoir.		[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that bitrate is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen bitrate; they need a higher [[bitrate]] than the defined one. Therefore, the MP3 spec defines a bit reservoir, intended especially to allow transient sounds to be encoded better.

	Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the [[Psychoacoustic#Psychoacoustic Model\|psymodel]] and the settings of the encoder) the CBR bitrate is set to 160 kbps. 30 bits are not used (160 - 130 = 30). those bits can be saved for following frames. To limit the streams complexity, the maximum reservoir size is 511 bytes (4088 bits) however this also limits the ability to cope with sustained complex passages of sound.		'''Example:'''

	With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the psymodel and the quality settings. So VBR (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (~~eg 160 - 130 = 30 spare~~ bits).		An MP3 file is to be encoded at 160 kbps CBR from CD source material, sampled at 44100 stereo samples per second.

			Because each MP3 frame is 1152 samples long, allowing 160000 bits per second, each frame can contain 4179 bits of data (= 160000 x 1152 / 44100).

			Imagine that a certain frame needs only 3056 bits to be properly encoded (as calculated by the [[Psychoacoustic#Psychoacoustic Model\|psymodel]] and the settings of the encoder). This is equivalent to about 117 kbps momentary bitrate (=3056 x 44100 / 1152). 1123 bits are not used (4179 - 3056 = 1123). Those bits together with any unused bits in the next few frames can be saved to a reservoir for use in following frames that may require more than 4179 bits each.

			To limit the stream's complexity, the maximum reservoir size is 4088 bits (511 bytes). If the maximum reservoir of 4088 bits is available in addition to the 4179 bits allocated by the 160 kbps CBR bitrate of our example, there are 8267 bits available, equivalent to a momentary bitrate of 316 kbps for one frame, but if used completely, no reservoir would be available to the very next frame, restricting that frame to 4179 bits (160 kbps), even if the psymodel deems that more than this is desirable. This limits the ability to cope with sustained passages of complex sound, but often proves adequate to cope with brief transients such as percussive sounds without setting the constant bitrate to, say, 320 kbps throughout the file.

			With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the psymodel and the quality settings. So VBR (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do so to collect bits that would otherwise be wasted to fill an available framesize. For example, our example frame requiring 3056 bits (117 kbps) might be stored in a 3343 bit frame (128 kbps) and donate the extra 287 bits to the reservoir, or it might be stored in a 2925 bit frame (112 kbps) using 131 bits from the existing bit reservoir from preceding frames to make up the shortfall.


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

Sebastian Mares at 13:56, 20 December 2010

2010-12-20T13:56:16Z

← Older revision		Revision as of 13:56, 20 December 2010
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	[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that bitrate is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen bitrate; they need a higher [[bitrate]] than the defined one. Therefore, the MP3 spec defines a bit reservoir.		[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that bitrate is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen bitrate; they need a higher [[bitrate]] than the defined one. Therefore, the MP3 spec defines a bit reservoir.

	Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the [[Psychoacoustic#Psychoacoustic Model\|psymodel]] and the settings of the encoder) the CBR bitrate is set to 160 kbps. 30 bits are not used (160 - 130 = 30). those bits can be saved for following frames. To limit the streams complexity, the maximum reservoir size is 511 bits however this also limits the ability to cope with sustained complex passages of sound.		Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the [[Psychoacoustic#Psychoacoustic Model\|psymodel]] and the settings of the encoder) the CBR bitrate is set to 160 kbps. 30 bits are not used (160 - 130 = 30). those bits can be saved for following frames. To limit the streams complexity, the maximum reservoir size is 511 bytes (4088 bits) however this also limits the ability to cope with sustained complex passages of sound.

	With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the psymodel and the quality settings. So VBR (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).		With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the psymodel and the quality settings. So VBR (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).

Pepoluan: Destroy redundant links

2006-10-02T21:30:33Z

Destroy redundant links

← Older revision		Revision as of 21:30, 2 October 2006
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	The term '''bit reservoir''' is used exclusively in the [[MP3]] specification.		The term '''bit reservoir''' is used exclusively in the [[MP3]] specification.

	[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that [[bitrate]] is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen [[bitrate]]; they need a higher [[bitrate]] than the defined one. Therefore, the [[MP3]] spec defines a bit reservoir.		[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that bitrate is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen bitrate; they need a higher [[bitrate]] than the defined one. Therefore, the MP3 spec defines a bit reservoir.

	Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the ~~psychoacoustic model~~ and the settings of the encoder) the [[CBR]] bitrate is set to 160 kbps. 30 bits are not used (160 - 130 = 30). those bits can be saved for following frames. To limit the streams complexity, the maximum reservoir size is 511 bits however this also limits the ability to cope with sustained complex passages of sound.		Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the [[Psychoacoustic#Psychoacoustic Model\|psymodel]] and the settings of the encoder) the CBR bitrate is set to 160 kbps. 30 bits are not used (160 - 130 = 30). those bits can be saved for following frames. To limit the streams complexity, the maximum reservoir size is 511 bits however this also limits the ability to cope with sustained complex passages of sound.

	With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the ~~[[Psychoacoustic#Psychoacoustic Model\|~~psymodel]] and the quality settings. So [[VBR]] (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).		With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the psymodel and the quality settings. So VBR (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).


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

Pepoluan: Fix link to PsyModel

2006-10-02T21:27:07Z

Fix link to PsyModel

← Older revision		Revision as of 21:27, 2 October 2006
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	~~=In~~ MP3:=		The term '''bit reservoir''' is used exclusively in the [[MP3]] specification.

	[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that [[bitrate]] is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen [[bitrate]]; they need a higher [[bitrate]] than the defined one. Therefore, the [[MP3]] spec defines a bit reservoir.		[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that [[bitrate]] is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen [[bitrate]]; they need a higher [[bitrate]] than the defined one. Therefore, the [[MP3]] spec defines a bit reservoir.
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	Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the psychoacoustic model and the settings of the encoder) the [[CBR]] bitrate is set to 160 kbps. 30 bits are not used (160 - 130 = 30). those bits can be saved for following frames. To limit the streams complexity, the maximum reservoir size is 511 bits however this also limits the ability to cope with sustained complex passages of sound.		Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the psychoacoustic model and the settings of the encoder) the [[CBR]] bitrate is set to 160 kbps. 30 bits are not used (160 - 130 = 30). those bits can be saved for following frames. To limit the streams complexity, the maximum reservoir size is 511 bits however this also limits the ability to cope with sustained complex passages of sound.

	With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the [[psymodel]] and the quality settings. So [[VBR]] (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).		With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the [[Psychoacoustic#Psychoacoustic Model\|psymodel]] and the quality settings. So [[VBR]] (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).


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

Pepoluan at 08:04, 2 September 2006

2006-09-02T08:04:26Z

← Older revision		Revision as of 08:04, 2 September 2006
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	With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the [[psymodel]] and the quality settings. So [[VBR]] (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).		With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the [[psymodel]] and the quality settings. So [[VBR]] (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).


			[[Category:Technical]]

Chigung: vbr does still use bit reservior - try comparing --nores encodes for proof. Also observe max bitreservoir of 511 with encspot (rather than320)

2005-05-09T02:24:48Z

vbr does still use bit reservior - try comparing --nores encodes for proof. Also observe max bitreservoir of 511 with encspot (rather than320)

← Older revision		Revision as of 02:24, 9 May 2005
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	[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that [[bitrate]] is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen [[bitrate]]; they need a higher [[bitrate]] than the defined one. Therefore, the [[MP3]] spec defines a bit reservoir.		[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that [[bitrate]] is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen [[bitrate]]; they need a higher [[bitrate]] than the defined one. Therefore, the [[MP3]] spec defines a bit reservoir.

	Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the psychoacoustic model and the settings of the encoder) the [[CBR]] bitrate is set to ~~192~~ kbps. 62 bits are not used (~~192~~ - 130 = 62). those bits can be ~~used~~ for the ~~next frame. This also works with consecutive frames~~, ~~until~~ the ~~point where~~ the ~~bitreservoir has the size~~ of ~~a 320 kbit frame~~.		Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the psychoacoustic model and the settings of the encoder) the [[CBR]] bitrate is set to 160 kbps. 30 bits are not used (160 - 130 = 30). those bits can be saved for following frames. To limit the streams complexity, the maximum reservoir size is 511 bits however this also limits the ability to cope with sustained complex passages of sound.

	With [[VBR]], the encoder can choose the needed framesize ~~at any~~ moment, again as defined by the [[psymodel]] and the quality settings. ~~That's why~~ [[VBR]] (e.g. in [[LAME]]) doesn't use bit reservoir.		With [[VBR]], the encoder can choose the needed framesize for each moment, again as defined by the [[psymodel]] and the quality settings. So [[VBR]] (e.g. in [[LAME]]) doesn't use bit reservoir nearly as much, but still may do to collect bits that would otherwise be wasted to fill an available framesize (eg 160 - 130 = 30 spare bits).

Jan at 10:46, 22 March 2005

2005-03-22T10:46:30Z

New page

=In MP3:=

[[CBR]] (and also to some degree [[ABR]]) uses a constant defined [[bitrate]]. Because that [[bitrate]] is taken into consideration at every frame, there will be certain moments of such complexity that they can't be properly encoded within the limitations of the chosen [[bitrate]]; they need a higher [[bitrate]] than the defined one. Therefore, the [[MP3]] spec defines a bit reservoir.

Example: a certain moment in a song needs 130 kbit to be accurately encoded (as defined by the psychoacoustic model and the settings of the encoder) the [[CBR]] bitrate is set to 192 kbps. 62 bits are not used (192 - 130 = 62). those bits can be used for the next frame. This also works with consecutive frames, until the point where the bitreservoir has the size of a 320 kbit frame.

With [[VBR]], the encoder can choose the needed framesize at any moment, again as defined by the [[psymodel]] and the quality settings. That's why [[VBR]] (e.g. in [[LAME]]) doesn't use bit reservoir.