6.1 and WebRTC codecs for web pages

The evaluation of 6.1 in an accessibility audit for the WAD is quite difficult without any technical information coming from the technical provider (e.g. black box evaluation). As the WebRTC standard is now mentioned in 6.2.3 (v4.1.1a), would it be possible to mention in 6.1 which WebRTC audio codecs are compliant with the requirements of 6.1?

Examples of compliant codecs, according to our analysis:

• Opus Wideband (WB)
• Opus Super Wideband (SWB)
• Opus Fullband (FB)
• G.722
• iSAC

Examples of non-compliant codecs, according to our analysis:

• Opus Narrowband (NB)
• Opus Mediumband (MB)
• G.711 PCM
• iLBC

Only Opus and G.711 PCM are required in all implementations of the WebRTC standard, according to RFC 7874.

The selection of an audio codec is done for every WebRTC audio connection and is based on a negociation between the client and the server. This negociation can be fine-tuned on the client-side to avoid some codecs.

Proposal: Include examples of WebRTC audio codecs which comply with 6.1: Opus Wideband, Opus Super Wideband, Opus Fullband, G.722, iSAC, and mention that G.711 PCM, which is an audio codec required for all WebRTC implementations, is not compliant with 6.1.

6.1_WebRTC_audio_codecs.xlsx

changed the description

changed the description

added RTT label

added Total Conversation label

RFC 7875 proposes addition of AMR-WB (=G722.2) and G.722 to the recommended audio codecs for WebRTC. It seems from the excel file in this issue as G.722 is generally accepted among web browsers. AMR-WB seems not yet to be widely accepted in browsers. AMR-WB would be to prefer if possible, because it takes only about 16 kbit/s for the same quality for which G.722 needs 64 kbit/s.
A similar format for 6.1 with a simple requirement and a note with a list of options for varying technical environments as for RTT in clause 6.2.10 (in the 4.1.1c version in #219 ) might be useful also for audio.

Do you think that, with the information provided by @vagnera, and the other information that you quote above, it would be possible to draft a potential note for 6.1 in a similar way to the one for 6.2.10. I suggested that you try this, as you have had a lot of practice at drafting and adapting the 6.2.10 note that would be hugely valuable!

Yes, I can try.

Total conversation is not discussed in this issue. I have removed the Total Conversation label.

removed Total Conversation label

Note X:  Specifications for audio codec implementation are provided for a number of technologies. The following list provides an overview of the situation at the time of authoring the present document. It is presented here as a guide for achieving interoperability and suitable quality. It should be noted that most audio codecs can be used with varying parameter settings resulting in varying quality and that listing of them here assumes that they are used with settings making them provide sufficient quality to meet the requirements in the present clause. All audio codecs for the technologies listed are using RFC 3550 RTP [i.50] for media transport:

a)          General VoIP and Multimedia communication: IETF, providing standards for Voice Over IP (VOIP) and Multimedia communications over IP based on the Session Initiation Protocol (SIP) IETF RFC 3261 [i.49]. In this technology, the following audio codecs with possibility for sufficient quality are commonly used: Recommendation ITU-T G.722 [i.21], Recommendation ITU‑T G.722.2 [i.22] also called AMR-WB. IETF RFC 6716 [ietfrfc6716] updated by IETF RFC 8251 [ietfrfc8251] called OPUS.

b)          IP Multimedia Sub-System (IMS): 3GPP, providing standards for mobile communication systems, including IP Multimedia Sub-System (IMS) has standardised the Multimedia Telephony concept, for communications with voice, video and RTT using the set of protocols specified in ETSI TS 126 114 (=3GPP TS 26.114) [i.10]. Multimedia Telephony is specified to use Recommendation ITU‑T G.722.2 [i.22] also called AMR-WB for wide band audio, and also EVS specified in ETSI TS 126 441 [i.ts126441]. For interoperability with other systems, Recommendation ITU-T G.722 [i.21] is specified.

c)          GSMA, providing selected profiles of standards for implementing globally interoperating mobile communications services has in GSMA PRD IR.92 [i.44] specified how to apply ETSI TS 126 114 [i.10] to implement RTT and Voice over LTE (VoLTE) and in GSMA PRD IR.94 [i.45] Video over LTE (ViLTE) in 4G mobile systems.. A similar document is published for RTT, voice and video over 5G in GSMA NG.114 [i.45]. Wide band audio is specified in these documents to use the same audio codecs as under b).

d)          Web technologies: For communication in Web Technologies, W3C and IETF have created the WebRTC concept specified in IETF RFC 8825 [i.ietfrfc8825] where the mandatory audio codecs with wide band audio capabilities are specified in IETF RFC 7874 [i.ietfrfc7874] to be Opus, while also Recommendation ITU-T G.722 [i.itutg722] is recommended by IETF RFC 7875 [i.ietfrfc7875] and usually provided in implementations.

e)          Emergency communications: An interface to IP based emergency communications is specified in TS 103 479 [i.47], making use of Recommendation ITU-T G.722.2 [i.itutg722] AMR-WB for wide-band audio . A corresponding standard exists for North America. For emergency apps, ETSI TS 103 478 [i.46] is specified in ETSI TS 103 945 [i.ts103945] to implement wide band audio by use of Opus IETF RFC 6716 [ietfrfc6716]. The use of these standards for accessible and interoperable emergency communications is specificed in ETSI TS 103 919 [i.55].

f)           Relay services: ETSI ES 202 975[i.5] specifies in its annexes A and B interfaces to relay services, referring to the present document for specific technologies.

Here is a version that should be exactly what you proposed, with just minor improvements to the English:

Note X:  Specifications for audio codec implementation are provided for a number of technologies. The following list provides an overview of the situation at the time of authoring the present document. It is presented here as a guide for achieving interoperability and suitable quality. It should be noted that most audio codecs can be used with varying parameter settings resulting in varying quality. They are listed here on the assumption that they are used with settings that allow them to provide sufficient quality to meet the requirements in the present clause. All audio codecs for the technologies listed are using RFC 3550 RTP [i.50] for media transport:

a)          General VoIP and Multimedia communication: IETF, providing standards for Voice Over IP (VOIP) and Multimedia communications over IP based on the Session Initiation Protocol (SIP) IETF RFC 3261 [i.49]. In this technology, the following audio codecs capable of delivering sufficient quality are commonly used: Recommendation ITU-T G.722 [i.21], Recommendation ITU‑T G.722.2 [i.22] also called AMR-WB. IETF RFC 6716 [ietfrfc6716] updated by IETF RFC 8251 [ietfrfc8251] called OPUS.

b)          IP Multimedia Sub-System (IMS): 3GPP, that provides standards for mobile communication systems, including IP Multimedia Sub-System (IMS) has standardised the Multimedia Telephony concept, for communications with voice, video and RTT using the set of protocols specified in ETSI TS 126 114 (=3GPP TS 26.114) [i.10]. Multimedia Telephony is specified to use Recommendation ITU‑T G.722.2 [i.22], also called AMR-WB for wide band audio, and also EVS specified in ETSI TS 126 441 [i.ts126441]. For interoperability with other systems, Recommendation ITU-T G.722 [i.21] is specified.

c)          GSMA, that provides selected profiles of standards for implementing globally interoperating mobile communications services, has in GSMA PRD IR.92 [i.44] specified how to apply ETSI TS 126 114 [i.10] to implement RTT and Voice over LTE (VoLTE) and, in GSMA PRD IR.94 [i.45], Video over LTE (ViLTE) in 4G mobile systems. A similar document is published for RTT, voice and video over 5G in GSMA NG.114 [i.45]. Wide band audio is specified in these documents to use the same audio codecs as under b).

d)          Web technologies: For communication in Web Technologies, W3C and IETF have created the WebRTC concept specified in IETF RFC 8825 [i.ietfrfc8825] where the mandatory audio codecs with wide band audio capabilities are specified in IETF RFC 7874 [i.ietfrfc7874] to be Opus, while Recommendation ITU-T G.722 [i.itutg722] is also recommended by IETF RFC 7875 [i.ietfrfc7875] and is usually provided in implementations.

e)          Emergency communications: An interface to IP based emergency communications is specified in TS 103 479 [i.47], it makes use of Recommendation ITU-T G.722.2 [i.itutg722] AMR-WB for wide-band audio. A corresponding standard exists for North America. For emergency apps, ETSI TS 103 478 [i.46] is specified in ETSI TS 103 945 [i.ts103945] to implement wide band audio by use of Opus IETF RFC 6716 [ietfrfc6716]. The use of these standards for accessible and interoperable emergency communications is specified in ETSI TS 103 919 [i.55].

f)           Relay services: ETSI ES 202 975[i.5] specifies in its annexes A and B interfaces to relay services, referring to the present document for specific technologies.

Opus and G.722 are on their way in to e) emergency communication TS 193 479 by EMTEL, in draft next version.

So, I suggest to accept the note above with the following addition to e)

IETF RFC 6716 [ietfrfc6716] updated by IETF RFC 8251 [ietfrfc8251] called OPUS, and Recommendation ITU-T G.722 [i.21].

So what would note e) look like after your addition". I see that note e) already includes RFC6716 and OPUS, so the addition would be a duplication. I am puzzled.

e) would be like this. I see that it is unpleasantly compact but works

e)          Emergency communications: An interface to IP based emergency communications is specified in TS 103 479 [i.47]. It makes use of Recommendation ITU-T G.722.2 [i.itutg7222] AMR-WB, IETF RFC 6716 [ietfrfc6716] updated by IETF RFC 8251 [ietfrfc8251] OPUS, and Recommendation ITU-T G.722 [i.21]. for wide-band audio. A corresponding standard exists for North America. For emergency apps, ETSI TS 103 478 [i.46] is specified in ETSI TS 103 945 [i.ts103945] to implement wide band audio by use of Opus IETF RFC 6716 [ietfrfc6716] updated by IETF RFC 8251 [ietfrfc8251] . The use of these standards for accessible and interoperable emergency communications is specified in ETSI TS 103 919 [i.55].

So, the final note to consider for agreement becomes:

Note X:  Specifications for audio codec implementation are provided for a number of technologies. The following list provides an overview of the situation at the time of authoring the present document. It is presented here as a guide for achieving interoperability and suitable quality. It should be noted that most audio codecs can be used with varying parameter settings resulting in varying quality. They are listed here on the assumption that they are used with settings that allow them to provide sufficient quality to meet the requirements in the present clause. All audio codecs for the technologies listed are using RFC 3550 RTP [i.50] for media transport:

a)          General VoIP and Multimedia communication: IETF, providing standards for Voice Over IP (VOIP) and Multimedia communications over IP based on the Session Initiation Protocol (SIP) IETF RFC 3261 [i.49]. In this technology, the following audio codecs capable of delivering sufficient quality are commonly used: Recommendation ITU-T G.722 [i.21], Recommendation ITU‑T G.722.2 [i.22] also called AMR-WB. IETF RFC 6716 [ietfrfc6716] updated by IETF RFC 8251 [ietfrfc8251] called OPUS.

b)          IP Multimedia Sub-System (IMS): 3GPP, that provides standards for mobile communication systems, including IP Multimedia Sub-System (IMS) has standardised the Multimedia Telephony concept, for communications with voice, video and RTT using the set of protocols specified in ETSI TS 126 114 (=3GPP TS 26.114) [i.10]. Multimedia Telephony is specified to use Recommendation ITU‑T G.722.2 [i.22], also called AMR-WB for wide band audio, and also EVS specified in ETSI TS 126 441 [i.ts126441]. For interoperability with other systems, Recommendation ITU-T G.722 [i.21] is specified.

c)          GSMA, that provides selected profiles of standards for implementing globally interoperating mobile communications services, has in GSMA PRD IR.92 [i.44] specified how to apply ETSI TS 126 114 [i.10] to implement RTT and Voice over LTE (VoLTE) and, in GSMA PRD IR.94 [i.45], Video over LTE (ViLTE) in 4G mobile systems. A similar document is published for RTT, voice and video over 5G in GSMA NG.114 [i.45]. Wide band audio is specified in these documents to use the same audio codecs as under b).

d)          Web technologies: For communication in Web Technologies, W3C and IETF have created the WebRTC concept specified in IETF RFC 8825 [i.ietfrfc8825] where the mandatory audio codecs with wide band audio capabilities are specified in IETF RFC 7874 [i.ietfrfc7874] to be Opus, while Recommendation ITU-T G.722 [i.itutg722] is also recommended by IETF RFC 7875 [i.ietfrfc7875] and is usually provided in implementations.

e)          Emergency communications: An interface to IP based emergency communications is specified in TS 103 479 [i.47]. It makes use of Recommendation ITU-T G.722.2 [i.itutg7222] AMR-WB, IETF RFC 6716 [ietfrfc6716] updated by IETF RFC 8251 [ietfrfc8251] OPUS, and Recommendation ITU-T G.722 [i.21]. for wide-band audio. A corresponding standard exists for North America. For emergency apps, ETSI TS 103 478 [i.46] is specified in ETSI TS 103 945 [i.ts103945] to implement wide band audio by use of Opus IETF RFC 6716 [ietfrfc6716] updated by IETF RFC 8251 [ietfrfc8251]. The use of these standards for accessible and interoperable emergency communications is specified in ETSI TS 103 919 [i.55].

f)           Relay services: ETSI ES 202 975[i.5] specifies in its annexes A and B interfaces to relay services, referring to the present document for specific technologies.

added Included in EN label

The proposed note has been included as Note 1 of the revised version of clause 6.1.1 in the latest editor's draft.

closed