There are many ways of achieving a hybrid of OTT-delivered and broadcast-delivered content, but they are not necessarily interoperable. DVB aims to solve the interoperability issue, along with the problem of service discovery with DVB-I. This specification was developed to bring linear TV over the internet up to the standard of traditional broadcast in terms of both video quality and user experience.
DVB-I supports any device with a suitable internet connection and media player, including TV sets, smartphones, tablets and media streaming devices. The medium itself can still be satellite, cable or DTT, but services are encapsulated in IP. Where both broadband and broadcast connections are available, devices can present an integrated list of services and content, combining both streamed and broadcast services.
DVB-I standard relies on three components developed separately within DVB: the low latency operation, multicast streaming and advanced service discovery. In this webinar, Rufael Mekuria from Unified Streaming focuses on low latency distributed workflow for encoding and packaging.
The process starts with an ABR (adaptive bit rate) encoder responsible for producing streams with multiple bit rates and clear segmentation – this allows clients to automatically choose the best video quality depending on available bandwidth. Next step is packaging where streaming manifests are added and content encryption is applied, then data is distributed through origin servers and CDNs.
Rufael explains that low latency mode is based on an enhancement to the DVB-DASH streaming specification known as DVB Bluebook A168. This incorporates the chunked transfer encoding of the MPEG CMAF (Common Media Application Format), developed to enable co-existence between the two principle flavors of adaptive bit rate streaming: HLS and DASH. Chunked transfer encoding is a compromise between segment size and encoding efficiency (shorter segments make it harder for encoders to work efficiently). The encoder splits the segments into groups of frames none of which requires a frame from a later group to enable decoding. The DASH packager then puts each group of frames into a CMAF chunk and pushes it to the CDN. DVB claims this approach can cut end-to-end stream latency from a typical 20-30 seconds down to 3-4 seconds.
The other topics covered are: encryption (exhanging key parameters using CPIX), content insertion, metadata, supplemental descriptors, TTML subitles and MPD proxy.
Of course without live ingest of content into the cloud, there is no live streaming so why would we leave such an important piece of the puzzle to an unsupported protocol like RTMP which has no official support for newer codecs. Whilst there are plenty of legacy workflows that still successfully use RTMP, there are clear benefits to be had from a modern ingest format.
Rufael Mekuria from Unified Streaming, introduces us to DASH-IF’s CMAF-based live ingest protocol which promises to solve many of these issues. Based on the ISO BMFF container format which underpins MPEG DASH. Whilst CMAF isn’t intrinsically low-latency, it’s able to got to much lower latencies than standard HLS, for instance.
This work to create a standard live ingest protocol was born out of an analysis, Rufael explains, of which part of the content delivery chain were most ripe for standardisation. It was felt that live ingest was an obvious choice partly because of the decaying RTMP protocol which was being sloppy replaced by individual companies doing their own thing, but also because there everyone contributing in the same way is of a general benefit to the industry. It’s not typically, at the protocol level, an area where individual vendors differentiate to the detriment of interoperability and we’ve already seen the, then, success of RMTP being used inter-operably between vendor equipment.
MPEG DAHS and HLS can be delivered in a pull method as well as pushed, but not the latter is not specified. There are other aspects of how people have ‘rolled their own’ which benefit from standardisation too such as timed metadata like ad triggers. Rufael, explaining that the proposed ingest protocol is a version of CMAF plus HTTP POST where no manifest is defined, shows us the way push and pull streaming would work. As this is a standardisation project, Rufael takes us through the timeline of development and publication of the standard which is now available.
As we live in the modern world, ingest security has been considered and it comes with TLS and authentication with more details covered in the talk. Ad insertion such as SCTE 35 is defined using binary mode and Rufael shows slides to demonstrate. Similarly in terms of ABR, we look at how switching sets work. Switching sets are sets of tracks that contain different representations of the same content that a player can seamlessly switch between.
“Standardisation is more than just a player format”. There’s so much to a streaming service than the video, a whole ecosystem needs to work together. In this talk from Comcast’s Mile High Video 2019, we see how different parts of the ecosystem are being standardised for live ingest.
RTMP and Smooth streaming are being phased out – without proper support for HEVC, VVC, HDR etc. they are losing relevance as well as, in the case of RTMP, support from the format itself. Indeed it’s clear that fragmented MP4 (fMP4) and CMAF are taking hold in their place so it makes sense for a new ingest standard to coalesce around these formats.
Rufael Mekuria from Unified streaming explains this effort to create a spec around live media ingest that is happening as part of MPEG DASH-IF. The work itself started at the end of 2017 with the aim of publishing summer 2019 supporting CMAF and DASH/HLS interfaces.
Rufael explains CMAF ingest used HTTP post to move each media stream to the origin packager. The tracks are separated into video, audio, timed text, subtitle and timed metadata. They are all transferred on separate tracks and is compatible with future codecs. He also covers security and timed text before covering DASH/HLS ingest which can also contain CMAF because HLS contains the capability to contain CMAF.
Reference software is available along with the <a href=”http://”https://dashif-documents.azurewebsites.net/Ingest/master/DASH-IF-Ingest.pdf” rel=”noopener noreferrer” target=”_blank”>specification.
Head of Research & Standardisation,
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