Hacker Guide/Audio Output - Revision history

DoesItReallyMatter: Light copy-edit

2019-05-30T22:36:47Z

Light copy-edit

← Older revision		Revision as of 22:36, 30 May 2019
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	{{Back to\|Hacker Guide}}		{{Back to\|Hacker Guide}}
	==Description==		==Description==
	An audio output module is used to pass decoded audio frames to the audio output hardware. Normally, the audio frames contain an integral number of audio samples coded linearly, i.e. [~~http~~:~~//en.wikipedia.org/wiki/~~Pulse-code~~%20modulation~~ PCM]. However, to address the need for digital audio pass-through, the audio output may also receive coded audio frames encapsulated as [~~http~~:~~//en.wikipedia.org/wiki/~~S/PDIF S/PDIF] packets.		An audio output module is used to pass decoded audio frames to the audio output hardware. Normally, the audio frames contain an integral number of audio samples coded linearly, i.e. [[wikipedia:Pulse-code modulation\|PCM]]. However, to address the need for digital audio pass-through, the audio output may also receive coded audio frames encapsulated as [[wikipedia:S/PDIF\|S/PDIF]] packets.

	This describes the fourth version of the audio output layer, found in [[VLC]] version 1.2.0. Versions 0.5.0 to 1.1.x were based on a partly similar but nevertheless incompatible interface known as aout3.		This describes the fourth version of the audio output layer, found in [[VLC]] version 1.2.0. Versions 0.5.0 to 1.1.x were based on a partly similar but nevertheless incompatible interface known as aout3.
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	Currently, the following formats are supported:		Currently, the following formats are supported:
	{\|		{\| class="mw-datatable sortable"
	!FOURCC		! scope="col" \| FOURCC
	!Description		! scope="col" \| Description
	!C ~~type~~		! scope="col" \| [[C Type]]
	!~~Endianess~~		! scope="col" \| Endianness
	!On entry		! scope="col" \| On entry
	!On return		! scope="col" \| On return
	\|-		\|-
	\|VLC_CODEC_FL32		\|VLC_CODEC_FL32
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	==== Convenience aliases ====		==== Convenience aliases ====
	VLC_CODEC_FL32 is an alias for VLC_CODEC_F32L or VLC_CODEC_F32B depending on architecture ~~endianess~~.		VLC_CODEC_FL32 is an alias for VLC_CODEC_F32L or VLC_CODEC_F32B depending on architecture endianness.
	The full list of convenience native ~~endianess~~ FOURCC is		The full list of convenience native endianness FOURCC is
	* VLC_CODEC_FL32 (float)		* VLC_CODEC_FL32 (float)
	* VLC_CODEC_FL64 (double)		* VLC_CODEC_FL64 (double)
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	If possible, it is recommended that the audio output uses a format as close to the input as possible. This is to conversion and loss of quality. Nevertheless, it is often necessary to use different a output format due to hardware limitation:		If possible, it is recommended that the audio output uses a format as close to the input as possible. This is to conversion and loss of quality. Nevertheless, it is often necessary to use different a output format due to hardware limitation:
	- resample if the aout->format.i_rate is modified,		* resample if the aout->format.i_rate is modified,
	- remix the channels if aout->format.i_physical_channels and/or aout->format.i_original_channels are modified,		* remix the channels if aout->format.i_physical_channels and/or aout->format.i_original_channels are modified,
	- convert the sample format is aout->format.i_format is modified.		* convert the sample format is aout->format.i_format is modified.

	=== Warning ===		=== Warning ===
	Beware that the Open() callback '''must not change''' aout->format until it is absolutely certain to return VLC_SUCCESS (0). If it were to change the format and then return an initialization failure, subsequent modules would get corrupt ~~informations~~ about the input format!		Beware that the Open() callback '''must not change''' aout->format until it is absolutely certain to return VLC_SUCCESS (0). If it were to change the format and then return an initialization failure, subsequent modules would get corrupt information about the input format!

	== Playback ==		== Playback ==
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	change_string_list (alsa_devices, alsa_devices_text, NULL)		change_string_list (alsa_devices, alsa_devices_text, NULL)
	</syntaxhighlight>		</syntaxhighlight>
	If however the underlying subsystem provides its own (per-application) settings, as is the case for [[PulseAudio]], there should not be any persistent configuration item. It would be ~~redumdant~~.		If however the underlying subsystem provides its own (per-application) settings, as is the case for [[PulseAudio]], there should not be any persistent configuration item. It would be redundant.

	{{Hacker_Guide}}		{{Hacker_Guide}}

	[[Category:Pages to check]]		[[Category:Pages to check]]

DoesItReallyMatter: +{{Back to|Hacker Guide}}

2019-04-17T06:38:05Z

+{{Back to|Hacker Guide}}

← Older revision		Revision as of 06:38, 17 April 2019
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			{{Back to\|Hacker Guide}}
	==Description==		==Description==
	An audio output module is used to pass decoded audio frames to the audio output hardware. Normally, the audio frames contain an integral number of audio samples coded linearly, i.e. [http://en.wikipedia.org/wiki/Pulse-code%20modulation PCM]. However, to address the need for digital audio pass-through, the audio output may also receive coded audio frames encapsulated as [http://en.wikipedia.org/wiki/S/PDIF S/PDIF] packets.		An audio output module is used to pass decoded audio frames to the audio output hardware. Normally, the audio frames contain an integral number of audio samples coded linearly, i.e. [http://en.wikipedia.org/wiki/Pulse-code%20modulation PCM]. However, to address the need for digital audio pass-through, the audio output may also receive coded audio frames encapsulated as [http://en.wikipedia.org/wiki/S/PDIF S/PDIF] packets.

DoesItReallyMatter: rel2abs, syntaxhighlight

2019-02-15T21:04:05Z

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DoesItReallyMatter: Added the page with :Category:Pages to check, note was on the talk page

2019-01-21T11:36:50Z

Added the page with Category:Pages to check, note was on the talk page

← Older revision		Revision as of 11:36, 21 January 2019
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	{{Hacker_Guide}}		{{Hacker_Guide}}

			[[Category:Pages to check]]

Corbax: /* Configuration */

2013-11-14T17:23:47Z

Configuration

← Older revision		Revision as of 17:23, 14 November 2013
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	If however the underlying subsystem provides its own (per-application) settings, as is the case for [[PulseAudio]], there should not be any persistent configuration item. It would be redumdant.		If however the underlying subsystem provides its own (per-application) settings, as is the case for [[PulseAudio]], there should not be any persistent configuration item. It would be redumdant.

	~~[[Category:Coding]]~~
	{{Hacker_Guide}}		{{Hacker_Guide}}

Corbax at 16:18, 30 October 2013

2013-10-30T16:18:59Z

← Older revision		Revision as of 16:18, 30 October 2013
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	[[Category:Coding]]		[[Category:Coding]]
	{{~~Documentation~~}}		{{Hacker_Guide}}

Edwardw: /* Volume management */

2013-10-19T02:32:29Z

Volume management

← Older revision		Revision as of 02:32, 19 October 2013
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	/* ...*/		/* ...*/
	}		}

			* '''aout''' is the audio output instance.
			* '''volume''' is a float (0.0f = 0% volume, 1.0f = 100% volume, 2.0f = 200% volume).
			* '''muted''' is true if muted.

	If the volume is modified asynchronously outside of LibVLC, the audio output module can notify LibVLC. This enables the VLC UI to show the correct value:		If the volume is modified asynchronously outside of LibVLC, the audio output module can notify LibVLC. This enables the VLC UI to show the correct value:

Edwardw: /* Priority */

2013-10-19T02:13:09Z

Priority

← Older revision		Revision as of 02:13, 19 October 2013
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	Unless a specific module has been provisioned in the VLC preferences, or specified through the --aout command line parameter, [[LibVLC]] will try to each audio output module in order of decreasing priority until one succeeds. As usual modules with a priority of zero will never be probed unless configured explicitly.		Unless a specific module has been provisioned in the VLC preferences, or specified through the --aout command line parameter, [[LibVLC]] will try to each audio output module in order of decreasing priority until one succeeds. As usual modules with a priority of zero will never be probed unless configured explicitly.

	Thus, on [[Linux]] for instance, the [[PulseAudio]] module has a higher priority than the [[ALSA]] one, and the [[OSS]] module has the smallest (non-zero) priority. The file audio output has zero priority and will not be used normally. This is so that VLC uses PulseAudio if available, otherwise ALSA, otherwise OSS.		Thus, on [[Linux]] for instance, the [[Documentation:Modules/pulse\|PulseAudio]] module has a higher priority than the [[Documentation:Modules/alsa\|ALSA]] one, and the [[Documentation:Modules/oss\|OSS]] module has the smallest (non-zero) priority. The file audio output has zero priority and will not be used normally. This is so that VLC uses PulseAudio if available, otherwise ALSA, otherwise OSS.

	== Initialization ==		== Initialization ==

Corbax: /* Configuration */

2013-10-01T14:45:43Z

Configuration

← Older revision		Revision as of 14:45, 1 October 2013
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	If however the underlying subsystem provides its own (per-application) settings, as is the case for [[PulseAudio]], there should not be any persistent configuration item. It would be redumdant.		If however the underlying subsystem provides its own (per-application) settings, as is the case for [[PulseAudio]], there should not be any persistent configuration item. It would be redumdant.

			[[Category:Coding]]
	{{Documentation}}		{{Documentation}}
	~~[[Category:Coding]]~~

Corbax at 14:39, 1 October 2013

2013-10-01T14:39:12Z

← Older revision		Revision as of 14:39, 1 October 2013
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	If however the underlying subsystem provides its own (per-application) settings, as is the case for [[PulseAudio]], there should not be any persistent configuration item. It would be redumdant.		If however the underlying subsystem provides its own (per-application) settings, as is the case for [[PulseAudio]], there should not be any persistent configuration item. It would be redumdant.

			{{Documentation}}
			[[Category:Coding]]