HNTF/Home Network TF Discussions/LipSyncTimeSynchronisation

Submitter: BBC

Tracker Issue ID: ISSUE-22

Description:

This use case is a specialisation of the use case: Time Synchronisation (issue-21)

An application should be able to synchronise the presentation of its own content with a high degree of accuracy to the timeline of a programme being played on a television or other home media rendering device. The level of accuracy should be sufficient to achieve 'lip-sync' between audio and video (typically within 1 to 2 video frames or tens of milliseconds).

In addition to the functions described in the Time Synchronisation use case; the API used by the application should be able to:

report an estimate of the timing synchronisation accuracy that is achievable
provide synchronisation to within lip-sync accuracy if all devices involved support it

The processing engine that implements the API may utilise existing home networking protocols to achieve the required accuracy. A likely necessary component will be the synchronisation of clocks between the television or media rendering device and the device on which the application is running. Possible protocols that might be used to achieve this include: Precision Time Protocol (IEEE 1588-2002) [1], IEEE 802.11AS, UPnP Precision Time Synchronization [2].

Applications will benefit if the API presents a simple simple unified set of functions such that the application does not need know which protocols are being used.

Scenario: An application plays alternative audio that is time synchronised to a programme that the user is watching. The synchronisation is sufficiently accurate to maintain 'lip-sync' between the alternative audio and the programme video. The alternative audio may be delivered to the application independently of the television device - such as via a direct stream from a broadcaster's internet based server.

[1] http://www.nist.gov/el/isd/ieee/ieee1588.cfm

[2] http://www.upnp.org/specs/av/UPnP-av-AVTransport-v3-Service.pdf

Justification:

Simplify creation of applications requiring lip-sync accurate time synchronisation that will work with a range of devices and variety of means by which a given programme might played on the television.
What could be standardised:
- Type of use case: Application specific services / protocols / APIs
- A Javascript API
- Services or protocols implemented by devices on the home network

Dependencies:

This use case is a specialisation of the Time Synchronisation use case

Comments: Jean-Claude Dufourd 17:33, 6 June 2011 (UTC) : This use case may well be technically impossible to achieve.