Standardised approach for OTT live streaming

IRT and partners demonstrate live CMAF sample Internet streams with IMSC1 subtitles

CMAF aims at unifying the two leading adaptive streaming standards which are MPEG-DASH and Apple’s HLS today. Technically, with CMAF, both HLS playlists and DASH manifests are allowed to reference the same fragmented MP4 (fMP4) chunks, whereas currently these chunks must be duplicated for each streaming mechanism.

Standardised approach for OTT live streaming on PC, mobile and SmartTV. Source: IRT

IRT, the research and competence centre for audio-visual technologies of the public broadcasters in Germany, Austria and Switzerland, in close cooperation with the IPTV and OTT solutions provider Keepixo and the German public broadcaster Bayerischer Rundfunk (BR) has provided sample live Internet streams demonstrating the potential benefit of the emerging Common Media Application Format (CMAF).

CMAF aims at unifying the two leading adaptive streaming standards which are MPEG-DASH and Apple’s HLS today. Technically, with CMAF, both HLS playlists and DASH manifests are allowed to reference the same fragmented MP4 (fMP4) chunks, whereas currently these chunks must be duplicated for each streaming mechanism. This allows any DASH player on Windows or Android to playback the exact same media segments as recent Apple devices (iOS10, tvOS, MacOS). Smart TVs based on HbbTV 1.5 and onwards support DASH-based streaming; therefore, CMAF also provides an important step towards the harmonization of HbbTV and HLS platforms.

For broadcasters the benefit of using CMAF for future OTT IP services lies in ist efficiency: only one packaging system is required and only one set of media chunks needs to be built. Consequently, also less storage space is needed for non-linear services such as catch-up TV, leading to lower storage costs. The viewer benefits as well, because HTTP caches in the delivery network become much more efficient, thus decreasing the risk of network congestion.

The implementation shows how future multiplatform access to adaptive streams can be realized. For the showcased streams prepared and live broadcast content has been encoded and packaged conform the CMAF specification. The demo streams are publicly available for anyone interested, specifically to demonstrate the potential of CMAF to service providers and to the industry.

CMAF also facilitates a better deployment of accessibility services. The sample streams contain deaf and hard of hearing subtitles in the IMSC1 format and can be extended by the alternative Web caption format WebVTT. This flexibility results in a better cross-platform support on mobile devices and Smart TVs. IRT supports this market harmonization through a long term dedication to subtitle format standardization. Audio Description, an accessibility service for the blind and visually impaired, is also contained in the sample streams; CMAF supports multiple audio tracks for video assets, without the need of duplication or repackaging the video. IRT cooperates with terminal- and encoder- manufacturers, as well as CDN- and cloud-providers, and offers end-to-end tests that are publicly available. To support interoperability between a maximum range of devices, IRT maintains an extensive repository of differently encoded Audio- and Video streams for PC, smartphones, tablets and HbbTV-devices on a test portal, to which CMAF test streams also have been added.

www.irt.de