OpusFAQ - Revision history

Jmspeex at 06:37, 13 April 2013

2013-04-13T06:37:49Z

← Older revision		Revision as of 06:37, 13 April 2013
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	If libopus is built with -DNONTHREADSAFE_PSEUDOSTACK (instead of VAR_ARRAYS, or USE_ALLOCA) it will use a user provided block of heap instead of stack for many things resulting in much lower the stack usage. However this makes the resulting library non-threadsafe and is not recommend on anything except limited embedded platforms.		If libopus is built with -DNONTHREADSAFE_PSEUDOSTACK (instead of VAR_ARRAYS, or USE_ALLOCA) it will use a user provided block of heap instead of stack for many things resulting in much lower the stack usage. However this makes the resulting library non-threadsafe and is not recommend on anything except limited embedded platforms.
		+
		+	=== How can I ensure that my software interoperates with other software implementing Opus? ===
		+
		+	For applications using Ogg files, there are some [http://people.xiph.org/~greg/opus_testvectors/ Ogg Opus testvectors] to test decoders and you can test encoders with opusdec. For RTP applications, the opusrtp tool can be useful. In general, here's a list of specific issues to check:
		+	* Can your application handle all frame sizes, including changing the frame size from frame to frame?
		+	* Does your application properly react to lost packet by calling the decoder with a NULL packet?

DOS386: added 2 (someone please check them)

2013-02-03T08:43:34Z

added 2 (someone please check them)

← Older revision		Revision as of 08:43, 3 February 2013
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	Opus is distinguished from most formats for high quality audio (AAC, Vorbis, MP3) by having low delay and it is distinguished from most low delay formats (G.711, GSM, Speex) by supporting high audio quality. It meets or exceeds existing codecs' quality across a wide range of bitrates, and it operates at lower delay than virtually any existing compressed format. Further, the Opus format itself and the reference implementation are available under liberal royalty-free licenses, making it easy to adopt, compatible with free software, and suitable for usage as part of the basic infrastructure of the Internet. See the Opus [http://opus-codec.org/comparison comparison page] for more details.		Opus is distinguished from most formats for high quality audio (AAC, Vorbis, MP3) by having low delay and it is distinguished from most low delay formats (G.711, GSM, Speex) by supporting high audio quality. It meets or exceeds existing codecs' quality across a wide range of bitrates, and it operates at lower delay than virtually any existing compressed format. Further, the Opus format itself and the reference implementation are available under liberal royalty-free licenses, making it easy to adopt, compatible with free software, and suitable for usage as part of the basic infrastructure of the Internet. See the Opus [http://opus-codec.org/comparison comparison page] for more details.
		+
		+	=== Does Opus make all those other lossy codecs obsolete? ===
		+
		+	Theoretically, yes. From technical point of view (loss, delay, bitrates, ...) it can replace both Vorbis and Speex, and the common proprietary codecs too.
		+
		+	=== Will Opus replace Vorbis in video files? ===
		+
		+	For OGG Theora video files, it can, just the overall size reduction will be minimal, and it will break compatibility with existing players.
		+
		+	For WebM video files, same does apply, but additionally this would need a change of the spec, as the current spec says that the only allowed video codec is VP8 and the only allowed audio codec is Vorbis.

	=== How do I use Opus? What programs support Opus? ===		=== How do I use Opus? What programs support Opus? ===

EvanCarroll at 19:14, 21 January 2013

2013-01-21T19:14:13Z

← Older revision		Revision as of 19:14, 21 January 2013
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	Opus being optimized for the Internet obviously means that it has good packet loss robustness and concealment, but it goes further. One of the first things we've been asked when designing Opus was to make the rate '''really''' adaptable because we never know what kind of rates will be available. This not only meant having a wide range of bitrates, but also being able to vary in small increments. This is why Opus scales from about 6 kb/s to 512 kb/s, in increments of 0.4 kb/s (one byte with 20 ms frames). The reason Opus can have more than 1200 possible bitrates spending 11 bits signalling the bitrate is because UDP already encodes the packet size. One last aspect is that Opus is simple to transport over RTP, as can be seen from [http://tools.ietf.org/html/draft-spittka-payload-rtp-opus Opus RTP payload format]. For example, it's possible to decode RTP packets without having even seen the SDP or any out-of-band signalling.		Opus being optimized for the Internet obviously means that it has good packet loss robustness and concealment, but it goes further. One of the first things we've been asked when designing Opus was to make the rate '''really''' adaptable because we never know what kind of rates will be available. This not only meant having a wide range of bitrates, but also being able to vary in small increments. This is why Opus scales from about 6 kb/s to 512 kb/s, in increments of 0.4 kb/s (one byte with 20 ms frames). The reason Opus can have more than 1200 possible bitrates spending 11 bits signalling the bitrate is because UDP already encodes the packet size. One last aspect is that Opus is simple to transport over RTP, as can be seen from [http://tools.ietf.org/html/draft-spittka-payload-rtp-opus Opus RTP payload format]. For example, it's possible to decode RTP packets without having even seen the SDP or any out-of-band signalling.
		+
		+	=== What applications for Android can play Opus? ===
		+
		+	Right now, there are just a few but that list is fast growing. Please reference [http://android.stackexchange.com/q/37970/7425 this question on android.stackexchange.com]. Feel free to suggest other applications.
		+

Prodicus: update to add vlc,ffmpeg to supporting apps after new releases; fix typos.

2012-10-19T23:07:40Z

update to add vlc,ffmpeg to supporting apps after new releases; fix typos.

← Older revision		Revision as of 23:07, 19 October 2012
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	=== How do I use Opus? What programs support Opus? ===		=== How do I use Opus? What programs support Opus? ===

-	Opus decoding support is now included in many applications, including Firefox and ~~Foobar2000~~, as well as in frameworks such as GStreamer. For now, the best way to '''encode''' Opus files is to use the opusenc command-line tool from the opus-tools package. For real-time applications, Opus support should soon be available in the Google webrtc codebase. Opus is still a new codec, expect many more applications to support it in the near future.	+	Opus decoding support is now included in many applications, including Firefox, foobar2000, and VLC, as well as in frameworks such as GStreamer and FFmpeg. For now, the best way to '''encode''' Opus files is to use the opusenc command-line tool from the opus-tools package. For real-time applications, Opus support should soon be available in the Google webrtc codebase. Opus is still a new codec, expect many more applications to support it in the near future.

	=== Does Opus support higher sampling rates, such as 96 kHz or 192 kHz? ===		=== Does Opus support higher sampling rates, such as 96 kHz or 192 kHz? ===
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	Yes.		Yes.

-	=== In what ~~way~~ is Opus optimized for the Internet? ===	+	=== In what ways is Opus optimized for the Internet? ===

	Opus being optimized for the Internet obviously means that it has good packet loss robustness and concealment, but it goes further. One of the first things we've been asked when designing Opus was to make the rate '''really''' adaptable because we never know what kind of rates will be available. This not only meant having a wide range of bitrates, but also being able to vary in small increments. This is why Opus scales from about 6 kb/s to 512 kb/s, in increments of 0.4 kb/s (one byte with 20 ms frames). The reason Opus can have more than 1200 possible bitrates spending 11 bits signalling the bitrate is because UDP already encodes the packet size. One last aspect is that Opus is simple to transport over RTP, as can be seen from [http://tools.ietf.org/html/draft-spittka-payload-rtp-opus Opus RTP payload format]. For example, it's possible to decode RTP packets without having even seen the SDP or any out-of-band signalling.		Opus being optimized for the Internet obviously means that it has good packet loss robustness and concealment, but it goes further. One of the first things we've been asked when designing Opus was to make the rate '''really''' adaptable because we never know what kind of rates will be available. This not only meant having a wide range of bitrates, but also being able to vary in small increments. This is why Opus scales from about 6 kb/s to 512 kb/s, in increments of 0.4 kb/s (one byte with 20 ms frames). The reason Opus can have more than 1200 possible bitrates spending 11 bits signalling the bitrate is because UDP already encodes the packet size. One last aspect is that Opus is simple to transport over RTP, as can be seen from [http://tools.ietf.org/html/draft-spittka-payload-rtp-opus Opus RTP payload format]. For example, it's possible to decode RTP packets without having even seen the SDP or any out-of-band signalling.
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	Even when FEC is not used, telling the encoder about the expected level of loss will help it make more intelligent decisions. By default the implementation assumes there is no loss.		Even when FEC is not used, telling the encoder about the expected level of loss will help it make more intelligent decisions. By default the implementation assumes there is no loss.

-	=== I can't use malloc or much stack on my embedded platform ~~how~~ do I make Opus work? ===	+	=== I can't use malloc or much stack on my embedded platform. How do I make Opus work? ===

	A normal build of libopus only uses malloc/free in the _create() and _destroy() calls, so Opus is safe for realtime use so long as the codec state is pre-created.		A normal build of libopus only uses malloc/free in the _create() and _destroy() calls, so Opus is safe for realtime use so long as the codec state is pre-created.

Martin.leese: /* What is Opus? Who created it? */ Tense

2012-09-12T20:04:44Z

What is Opus? Who created it?: Tense

← Older revision		Revision as of 20:04, 12 September 2012
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	=== What is Opus? Who created it? ===		=== What is Opus? Who created it? ===

-	Opus is a totally open, royalty-free, highly versatile audio codec. It is primarily designed for interactive speech and music transmission over the Internet, but is also applicable to storage and streaming applications. It incorporates technology from Skype's SILK codec and Xiph.Org's CELT codec. It ~~is being~~ standardized by the Internet Engineering Task Force (IETF) as '''[http://tools.ietf.org/html/rfc6716 RFC 6716]'''.	+	Opus is a totally open, royalty-free, highly versatile audio codec. It is primarily designed for interactive speech and music transmission over the Internet, but is also applicable to storage and streaming applications. It incorporates technology from Skype's SILK codec and Xiph.Org's CELT codec. It has been standardized by the Internet Engineering Task Force (IETF) as '''[http://tools.ietf.org/html/rfc6716 RFC 6716]'''.

-	Opus has been in development since early 2007. Programmers associated with Xiph.Org, Skype, and several other organizations have contributed to its development and to the standardization process as part of the IETF's codec working group.	+	Opus has been in development since early 2007. Programmers associated with Xiph.Org, Skype, and several other organizations have contributed to its development and to the standardization process as part of the IETF's codec working group.

	=== How does Opus compare to other codecs? ===		=== How does Opus compare to other codecs? ===

Jmspeex at 16:45, 11 September 2012

2012-09-11T16:45:47Z

← Older revision		Revision as of 16:45, 11 September 2012
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	Unlike most ITU-T codecs, Opus is only defined in terms of its decoder. The encoder can keep evolving as long as the bitstream it produces can be decoded by the reference decoder. This is what made it possible for MP3 encoders to improve far beyond the original l3enc and the dist10 reference implementation. Although it is unlikely that Opus encoders will see such spectacular evolution, we certainly hope that future encoders will become much better than the reference encoder. In fact, there is already an [http://www.opus-codec.org/development/ experimental branch] that significantly improves on the reference encoder's quality.		Unlike most ITU-T codecs, Opus is only defined in terms of its decoder. The encoder can keep evolving as long as the bitstream it produces can be decoded by the reference decoder. This is what made it possible for MP3 encoders to improve far beyond the original l3enc and the dist10 reference implementation. Although it is unlikely that Opus encoders will see such spectacular evolution, we certainly hope that future encoders will become much better than the reference encoder. In fact, there is already an [http://www.opus-codec.org/development/ experimental branch] that significantly improves on the reference encoder's quality.
		+
		+	=== Will all future Opus releases comply with the [http://tools.ietf.org/html/rfc6716 Opus specification]? ===
		+
		+	Yes.

	=== In what way is Opus optimized for the Internet? ===		=== In what way is Opus optimized for the Internet? ===

Jmspeex at 04:47, 11 September 2012

2012-09-11T04:47:14Z

← Older revision		Revision as of 04:47, 11 September 2012
Line 42:		Line 42:

	Unlike most ITU-T codecs, Opus is only defined in terms of its decoder. The encoder can keep evolving as long as the bitstream it produces can be decoded by the reference decoder. This is what made it possible for MP3 encoders to improve far beyond the original l3enc and the dist10 reference implementation. Although it is unlikely that Opus encoders will see such spectacular evolution, we certainly hope that future encoders will become much better than the reference encoder. In fact, there is already an [http://www.opus-codec.org/development/ experimental branch] that significantly improves on the reference encoder's quality.		Unlike most ITU-T codecs, Opus is only defined in terms of its decoder. The encoder can keep evolving as long as the bitstream it produces can be decoded by the reference decoder. This is what made it possible for MP3 encoders to improve far beyond the original l3enc and the dist10 reference implementation. Although it is unlikely that Opus encoders will see such spectacular evolution, we certainly hope that future encoders will become much better than the reference encoder. In fact, there is already an [http://www.opus-codec.org/development/ experimental branch] that significantly improves on the reference encoder's quality.
		+
		+	=== In what way is Opus optimized for the Internet? ===
		+
		+	Opus being optimized for the Internet obviously means that it has good packet loss robustness and concealment, but it goes further. One of the first things we've been asked when designing Opus was to make the rate '''really''' adaptable because we never know what kind of rates will be available. This not only meant having a wide range of bitrates, but also being able to vary in small increments. This is why Opus scales from about 6 kb/s to 512 kb/s, in increments of 0.4 kb/s (one byte with 20 ms frames). The reason Opus can have more than 1200 possible bitrates spending 11 bits signalling the bitrate is because UDP already encodes the packet size. One last aspect is that Opus is simple to transport over RTP, as can be seen from [http://tools.ietf.org/html/draft-spittka-payload-rtp-opus Opus RTP payload format]. For example, it's possible to decode RTP packets without having even seen the SDP or any out-of-band signalling.

Jmspeex at 05:13, 31 August 2012

2012-08-31T05:13:27Z

← Older revision		Revision as of 05:13, 31 August 2012
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	=== Does Opus support higher sampling rates, such as 96 kHz or 192 kHz? ===		=== Does Opus support higher sampling rates, such as 96 kHz or 192 kHz? ===

-	Yes and no. Opus encoding tools like opusenc will happily encode files that are sampled at 96 or 192 kHz~~. Decoders are free to output at these rates; in particular, by default, opusdec will output at the sampling rate of the original file~~. However, input at these rates is internally converted to 48 kHz, and then only frequencies up to 20 kHz are encoded. The reason is simple: lossy codecs are designed to preserve audible ~~detail~~ while discarding irrelevant information. Since the human ear can only hear up to 20 kHz at best (usually lower than that), frequency content above 20 kHz is the first thing to go. See ~~Chris Montgomery~~'s [http://people.xiph.org/~xiphmont/demo/neil-young.html 24/192 Music Downloads ...and why they make no sense] for more details.	+	Yes and no. Opus encoding tools like opusenc will happily encode files that are sampled at 96 or 192 kHz. However, input files at these rates are internally converted to 48 kHz, and then only frequencies up to 20 kHz are encoded. The reason is simple: lossy codecs are designed to preserve audible details while discarding irrelevant information. Since the human ear can only hear up to 20 kHz at best (usually lower than that), frequency content above 20 kHz is the first thing to go. See Monty's [http://people.xiph.org/~xiphmont/demo/neil-young.html 24/192 Music Downloads ...and why they make no sense] for more details.

	=== What are the licensing requirements? ===		=== What are the licensing requirements? ===

Jmspeex at 05:09, 31 August 2012

2012-08-31T05:09:51Z

← Older revision		Revision as of 05:09, 31 August 2012
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	=== How do I use Opus? What programs support Opus? ===		=== How do I use Opus? What programs support Opus? ===

-	Opus decoding support is now included in many applications, including Firefox and Foobar2000, as well as in frameworks such as GStreamer. For now, the best way to '''encode''' Opus files is to use the opusenc command-line tool from the opus-tools package. For real-time applications, Opus support should soon be available in the Google webrtc codebase.	+	Opus decoding support is now included in many applications, including Firefox and Foobar2000, as well as in frameworks such as GStreamer. For now, the best way to '''encode''' Opus files is to use the opusenc command-line tool from the opus-tools package. For real-time applications, Opus support should soon be available in the Google webrtc codebase. Opus is still a new codec, expect many more applications to support it in the near future.

	=== Does Opus support higher sampling rates, such as 96 kHz or 192 kHz? ===		=== Does Opus support higher sampling rates, such as 96 kHz or 192 kHz? ===

Jmspeex at 05:08, 31 August 2012

2012-08-31T05:08:27Z

← Older revision		Revision as of 05:08, 31 August 2012
Line 11:		Line 11:
	=== How does Opus compare to other codecs? ===		=== How does Opus compare to other codecs? ===

-	Opus is distinguished from most formats for high quality audio (AAC, Vorbis, MP3) by having low delay and it is distinguished from most low delay formats (G.711, GSM, Speex) by supporting high audio quality. It meets or exceeds existing codecs' quality across a wide range of bitrates, and it operates at lower delay than virtually any existing compressed format. Further, the Opus format itself and the reference implementation are available under liberal royalty-free licenses, making it easy to adopt, compatible with free software, and suitable ~~for~~ for usage as part of the basic infrastructure of the Internet. See the Opus [http://opus-codec.org/comparison comparison page] for more details.	+	Opus is distinguished from most formats for high quality audio (AAC, Vorbis, MP3) by having low delay and it is distinguished from most low delay formats (G.711, GSM, Speex) by supporting high audio quality. It meets or exceeds existing codecs' quality across a wide range of bitrates, and it operates at lower delay than virtually any existing compressed format. Further, the Opus format itself and the reference implementation are available under liberal royalty-free licenses, making it easy to adopt, compatible with free software, and suitable for usage as part of the basic infrastructure of the Internet. See the Opus [http://opus-codec.org/comparison comparison page] for more details.

	=== How do I use Opus? What programs support Opus? ===		=== How do I use Opus? What programs support Opus? ===