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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 its 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.
The showcase with the sample stream can be viewed on the following demo website:
IRT’s AV Streaming test portal can be accessed under following link:
The partners have contributed to the showcase as follows:
“At Keepixo, we’re always striving to add the latest features that the TV industry needs.” said Jerome Blanc, COO of Keepixo. “The recent addition of CMAF to our OTT packager is the perfect example of how we can address the entire OTT TV spectrum, and help operators reduce their costs and improve their subscribers’ experience.” Keepixo’s packager is a flexible, feature-rich live OTT packager, which can be provided as a stand-alone solution or integrated within Keepixo’s live multirate OTT transcoder.
BR provided the content for the “semi-live” looped CMAF stream which can be accessed worldwide without geo-blocking.
IRT coordinated the efforts and reviewed the sample streams. “IRT is investigating alternative streaming methods to HLS-delivery or MPEG-DASH-delivery to find more efficient and thus less expensive workflows for IP-based distribution” says Dr. Klaus Illgner-Fehns, CEO of IRT. “Besides mechanisms for adaptive media transport, also the joined carriage of program-associated data like subtitles is evaluated. In this context CMAF provides promising options.”