| RFC 9695 | The 'haptics' Top-level Media Type | December 2024 |
| Muthusamy & Ullrich | Standards Track | [Page] |
This memo registers and documents the 'haptics' top-level media type, under which subtypes for representation formats for haptics may be registered. This document also serves as a registration for a set of subtypes, which are representative of some existing subtypes already in use.¶
This is an Internet Standards Track document.¶
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9695.¶
Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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The term 'haptics' refers to the generation of touch-related sensations in a device or interface. Haptics is widely used in consumer devices in order to provide touch-based feedback to users. The most common use of haptics is in mobile devices, where it is used to provide feedback to users interacting with the touchscreen, e.g., typing on a virtual keyboard. Haptic technologies are unlike audio and visual enabling technologies in the sense that they require some form of actuation in order to create a tactile sensation. For mobile phones and game controllers, these actuators are typically small vibrating motors. For large touchscreens in vehicles, these actuators can be specialized piezoelectric materials. Haptic capabilities are found in nearly every modern smartphone, game, and virtual reality controller, making these devices an ideal target for enhanced media experiences.¶
Internet Media Types [RFC6838] are used to label content carried over Internet protocols. This document defines a new top-level type, 'haptics', according to [RFC9694]. This top-level type indicates that the content specifies haptic data. Under this top-level type, different representation formats of haptics may be registered.¶
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
Haptic signals provide an additional layer of entertainment and sensory immersion for the user, when combined with audio and video signals. Haptic tracks, in separate files, can be combined with audio/video files and played back in sync to provide an overall immersive media experience (audio, visual, tactile) for the user. More recently, haptic tracks embedded in standard file formats, such as ISOBMFF (ISO Base Media File Format), enable playback of the haptic signals over one or more actuators, simultaneously with audio and video playback [ISOBMFF-IS]. Haptic signals are also part of media streams that use RTP, such as those for streaming games, XR, and wearables.¶
Historically, there has not been a registration of formats for haptics. However, haptics was proposed as a first-order media type (at the same level as audio and video) in ISOBMFF in April 2020. The proposal has since progressed to International Standard, and was published in January 2022 [ISOBMFF-IS]. Haptics is officially part of the ISO/IEC 14496-12 (ISOBMFF) standard, 7th Edition. Given this development, a strong case can be made for haptics to be added to the list of top-level media types recognized by the IETF.¶
We envision the following designations for haptics in mp4 files, once the top-level type 'haptics' is registered:¶
There are multiple sub-modalities of haptics:¶
Therefore, designating 'haptics' as a top-level media type enables the definition of data formats pertaining to these sub-modalities in a more streamlined manner. This would not be possible if 'haptics' were to be placed under other top-level types like 'audio', 'video', or 'application'.¶
The top-level media type 'audio' pertains to the human sense of hearing; the top-level media type 'video' pertains to the human sense of seeing; so it only makes sense for the (equally important) human sense of touch to be represented by another top-level media type 'haptics'. Placing 'haptics' under 'audio' or 'video' is not reflective of the kinds of files or use cases that would need haptics but have nothing whatsoever to do with audio or video.¶
Haptics is rapidly becoming a standard feature of consumer electronic devices. For example:¶
Haptic media is expected to be commonly exchanged between these devices. Since they represent the majority of CE devices, a strong case can be made for 'haptics' as a top-level media type.¶
There are multiple instances of existing haptic data formats that will live as sub-types under the proposed 'haptics' top-level media type. While these subtypes have *not* been registered with IANA or standardized (yet), the prevalence of these haptic data formats in a large number of devices around the world, pre-dating the standardization of haptic tracks in ISOBMFF, provides a compelling argument for 'haptics' to be designated as a top-level media type:¶
'ivs': The IVS haptic data format [MPEG-Haptics-Encoder] is in use:¶
'hapt': The HAPT haptic data format is currently a vendor-specific format that is in use:¶
The following Japanese game developers use the HAPT format as part of Immersion's TouchSense SDK:¶
Given the widespread use of these subtypes, it makes sense for 'haptics' to be a top-level media type.¶
The MPEG ISOBMFF proposal included an informative annex of known haptic coding formats with proposed FourCCs (four-character codes) for them. These codes are not registered yet, but the plan is indeed to standardize these haptic coding formats in the near future. Once standardized, these types should also be registered as subtypes of the 'haptics' top-level media type:¶
From the above arguments, it is clear that haptics does not really belong under any other media type. To reiterate, there are three main reasons why the 'haptics' media type does not fit under the 'application' top-level type:¶
Haptics are interpreted data structures that represent collections of different media rendering instructions intended to be decoded and rendered on target device hardware. Haptic data can be represented as collections of signal data and/or descriptive text in XML/JSON or a similar format. Signal data is typically not executed by endpoint processors and represents minimal security risk. Descriptive text is typically parsed and represented in memory using standard XML data structures. This data is utilized to construct one or more signals that are sent to the endpoint device hardware.¶
Because of the media/rendering nature of the data path for haptic-coded data, the security profile of haptic data is expected to be largely consistent with the security profile of visual and audio media data.¶
As with any synthesized media data (audio, video, and haptics), there is a security risk associated with execution of commands based on the descriptive encoding either through its inherent extensibility or through the insertion of arbitrary executable data in the descriptive format itself. Indeed, media rendering systems are normally implemented with a mix of user and kernel space execution since these media must ultimately make their way to a hardware system. In theory, malicious instructions present in descriptive haptic media have the potential to execute arbitrary code in kernel space, effectively bypassing system permissions structures and/or execution sandboxes.¶
Haptics, audio, and video media have widespread use and careful attention should be paid by operating system and device driver implementors to ensure that synthesis and rendering signal paths do not provide attack surfaces for malicious payloads.¶
Thermal haptic devices (that provide a sensation of heat) and kinesthetic haptic devices (that provide force feedback) could potentially injure users if the heat or force, respectively, are not properly controlled or inadvertently exceed safety levels. Implementors need to ensure that adequate measures are taken to prevent such scenarios.¶
These security considerations apply to the subtype registrations described in this document as well as all future haptics registrations.¶
IANA has registered 'haptics' in the "Top-Level Media Types" registry defined in [RFC9694] and registered several subtypes. IANA has also added 'haptics' as an alternative value of "Type Name" in the media types registration form [Media-Type-Reg].¶
'haptics' is the primary media content type that indicates the content identified by it requires a certain haptics subsystem such as low-level haptics APIs, which in turn will require hardware capabilities such as one or more actuators to render the haptics media. The 'haptics' media type does not provide any specific information about the underlying data format and how the haptics information should be interpreted -- the subtypes defined within a 'haptics' tree name the specific haptic formats. Unrecognized subtypes of 'haptics' should be treated as 'application/octet-stream'. Implementations may still pass unrecognized subtypes to the haptics subsystem and associated rendering hardware.¶
New haptics formats should be requested using the Application for a Media Type online form [Media-Type-Reg]. [RFC6838] should be consulted on registration procedures. In particular, the haptics specification should preferably be freely available.¶
Note that new subtypes may define parameters. If an implementation does not recognize a parameter sub-value in the comma-separated list, it should ignore the sub-value and continue processing the other sub-values in the list.¶
In this section, the initial entries under the top-level 'haptics' media type are specified. They also serve as examples for future registrations.¶