Sunday, March 24, 2013

SERTA? ZA?PUS: Over-The-Top (OTT) Streaming and Adaptive Bit ...

OTT (Over-The-Top) streaming is the delivery of video and audio media streams to connected devices via the Internet. Unlike traditional IPTV, there is no need for a dedicated network or infrastructure provided by the operator, as OTT is transported through regular Internet data protocols and uses the open Internet, on unmanaged networks.
What is the difference between OTT and IPTV?

IPTV ? IP work of DVB world:

  • Traditional IPTV which has been widely deployed by numerous operators, namely those that propose a triple-play ADSL offer to their customers.
  • This traditional IPTV is delivered over a dedicated, operator-managed network that is used only for broadcasting TV.
  • ?The operator has full control over the network and can configure certain parameters, such as bandwidth consumption and regularity of packet transportation, to ensure a high level of service quality.
  • Traditional IPTV uses TS (transport stream) transmission technology which is based on satellite TV broadcasting and delivers content over UDP in datagram mode.

OTT ? TV work of IT world:

  • OTT TV uses HTTP, the protocol which has been used for decades to transport web pages over the Internet.
  • HTTP is based on TCP, a connected transport protocol with more practical features than UDP. It is easier to track a TCP connection, for example. As a result, a TCP connection is easily managed through firewalls, NAT (network address translation), home and office networks.
  • It also enables anyone that has sufficient web hosting capacity to broadcast any audio and video media to a worldwide audience over the open Internet.
  • HTTP has already been used as a transport solution for video on demand (VOD) media embedded into web pages, especially on Flash-based sites, such as YouTube or Dailymotion.
  • However this solution does not use real time streaming, but progressive downloading of one media file, where the browser downloads the file from the HTTP web server and when it has a sufficient amount of data, starts to play the content while downloading the rest of the file.The main drawback to this approach is the length of time it takes to fill the initial buffer.
  • Another issue associated with http is streaming quality, which depends on the IP connection.
  • Content streaming may be subject to stalling if there are fluctuations in bandwidth, leading to frame freezing. As a consequence, it is nearly impossible to use the solution to broadcast live channels.
  • Until recently, live broadcasting was therefore restricted to operator-managed IPTV networks using the UDP multicast protocol.
  • The arrival of OTT streaming, however, has brought a new approach and it is now possible to achieve levels of streaming quality over HTTP that allow live content to also be broadcast over the Internet.

Adaptive Bit Rate (Abr)

As the open Internet is by definition an ?unmanaged? network, the end-user bandwidth cannot be controlled. This can lead to low streaming quality and negatively impact the user experience when watching TV. The proposed technology must be adapted for use on a full range of end-user devices (PC web browsers, STB/TV, mobile handsets, digital tablets, etc). Currently, there are three big players who propose their own solutions to the challenges of OTT: 1.???? Apple?, promoting its HLS standard; 2.???? Google?, pushing its own WebM technology; 3.???? Microsoft?, with Silverlight Smooth Streaming. Building Market and Meeting the Players: High quality video delivery was the monopoly of managed network players, i.e. telecom operators (telcos) and Internet Service Providers (ISPs). OTT enables new players to enter the game by creating a direct connection between the content providers (TV channels, content aggregators, satellite and cable broadcasters) and the end users. It enables the content providers to promote their video services directly to the viewer. Most content providers have suffered from the telco/broadcast war for end user management, and telcos have gained a significant advantage through IPTV and VOD offers that are included in triple-play packages. With OTT, content providers will be able to get their revenge by marketing and delivering their content directly to TV and mobile device viewers. Before the arrival of OTT technologies, video delivery was mainly limited to PCs and some high-end mobiles phones. We now see the emergence of Connected TVs, and connected TV enables consumer electronics manufacturers to bring value to TV delivery because it allows direct contact between the viewers and the content providers. Another new market which has emerged from OTT content availability is the tablet market. Other examples of new emerging players able to take advantage of the opportunity in OTT are the electronic retailers who already have partnerships on the fixed and mobile telco markets, and MVNOs (mobile virtual network operators). Their core business is to deliver devices to consumers such as TV sets, tablets and other connected video equipment. OTT can enable them to leverage their CRM (customer relationship management) with a complementary video offer, linked to the electronic devices they are distributing.

Apple introduced HTTP Live Streaming (HLS) in June 2009 with their iPhone? OS 3.0 (which has since been renamed iOS). HLS streaming is without any doubt the most widespread protocol used for OTT, as it is available on all Apple devices (iPhone, iPad, iPod?, Apple TV?...) as well as on some software players and a number of set top boxes.?
The operating principle of HLS is to work with segmented TS-based video streams or files.

  • The chosen container for HLS is thus an MPEG transport stream (TS), also used for satellite broadcasting and IPTV on managed networks.
  • The chosen codec is MPEG H.264 for video and AAC for audio, which have also been widely used in the broadcast industry for many years.

The approach taken by Apple is very interesting. It is based on using proven industry standards and modifying them slightly in order to fit with the requirements of an OTT solution. The less the modifications impact existing standards and technologies, the faster HLS will integrate into existing ecosystems.

The way to achieve HLS streaming is to:
  • Encode video in H.264/TS format (taken from live feed or from a file), in different bitrates;
  • Use a stream segmenter to generate short ?chunks? of content ? typically 10 seconds each ?
  • Generate a playlist file (m3u or m3u8) indicating where to download the chunks;
  • Distribute through a HTTP server, and provide appropriate caching.

Another strength of HLS is its ability to implement adaptive bitrate intelligently. Contrary to the techniques that are used in mobile RTP streaming, it is the end user device that decides the stream quality, according to the available bandwidth (and not the video server). This approach aims to ensure unbroken video streaming, thus creating a positive user experience on an unmanaged network:

Index file is generated indicating different profiles (streaming qualities) available for one channel/content file;

The receiving device (PC, mobile, STB) looks for the most suitable bitrate based on how long it takes to receive a chunk file;

Each chunk file lasts 10 seconds, so the receiving device can automatically adapt the streaming with flexibility ? in this case, every 10 seconds.


  • It provides a simple and efficient adaptive bitrate solution to cope with the fact that bandwidth is not managed on open networks.
  • It is easy to integrate at the reception device level and can therefore be deployed on a wide range of set-top-boxes and devices.
  • It is based on Transport Stream transmission technology, making it easy to integrate into the existing digital TV world. A lot of IPTV DRM providers have already adopted this standard.


  • ?The adaptive bitrate solution is located solely in the device client. This ?democratic? approach could hinder some uses in the professional / corporate world where administrators may wish to fine-tune the available video quality for certain specific content.
  • As Apple didn?t propose its own client software for Windows PC, there is no native support in the major web browsers, and the lack of plugins to simplify integration makes it difficult to use as a web TV standard.
  • Being limited to the MPEG standards means that the providers of HLS-compatible equipment may be liable to pay a license fee to MPEG LA. While it is no problem for Apple to pay an additional few cents in licensing fees when they sell iPhones, iPods or iPads that cost several hundreds of dollars, it may be a significant barrier for players in the ?free and open-source? culture ? namely the web browser providers who do not sell their products. Mozilla Foundation or Opera Software would not be very pleased to pay royalties to MPEG LA every time their browser software is downloaded. Recently, MPEG LA chose to soften their politics regarding free content over the Internet, but their global position remains unclear.
  • DRM encryption is done through the encryption of the entire chunks. The transport layer is thus also encrypted, which is a barrier for some features, such as dynamic trick modes.

Google WebM

WebM was announced in May 2010, during Google I/O 2010. Promotion of the technology made it clear that WebM aimed to provide an OTT solution that would be royalty-free and usable on an open basis by all Internet companies and communities. In order to achieve this,

  • Google decided to provide its VP8 video codec under a BSD license.
  • The chosen audio codec is Vorbis, and the container is based on a profile from Matroska.
?WebM does not require segmentation of the media into chunks, because with WebM, one media stream is seen as one file. To stream WebM from a live or VOD file:
  • Encode the video and audio content in VP8 and Vorbis respectively, in different bitrates;
  • Mux them into a WebM file, which must be automatically refreshed in real time if you plan to do live streaming;
  • Use a HTTP server to deliver the WebM file.

Note that there is an added complexity to live TV streaming, where the muxing must be done constantly, and the resulting file will never be the same over time. As a result, caching on WebM is much more difficult than with chunks of video files. This makes it difficult to integrate added-value features such as trick play, playlist or circular buffer.

WebM is also very different from the other OTT solutions because it is the server that chooses the audio/video streaming bitrate before muxing. The server has an output buffer in which it pushes all the packets ready to be sent. As it sends the content of the buffer to the network, it detects if there is enough bandwidth to reach the client. If not, it scales down to a lower bitrate.


  • The choice of Matroska for the container profile is interesting: Matroska uses EBML, a binary format derivative of XML. It allows the capabilities of the container to be extended without breaking the compatibility with older parsers. For example, it already includes a menu system (similar to the ?chapters? of a DVD) and supports multiple audio and video tracks with labels attached to them, clean 3D handling, closed captions and subtitles, etc.
  • Moreover, Matroska uses less bandwidth than TS encapsulation ? this is an important point, especially for mobile devices.
  • Native playback for three of the main web browsers is also an advantage. If you have ever tried to watch a Flash-based video clip using LinuxOS, you should know that plugins are not necessarily very stable.
  • The adaptive bitrate is managed by the server, but there are tricks that can enable the client software to ask the server to switch to higher or lower bitrate.


  • The lack of chips currently available for VP8 hardware decoding is a major drawback for WebM. When compared to the support of H.264, which has become very common on medium to high-range mobile devices, it is a good illustration of the difficulty in imposing a new codec to the industry.
  • In addition to the codec issue, and contrary to HLS, there is also the fact that the STBs have to support the Matroska container. While it?s not a significant issue for players from the web environment, it may become one for those who come from the satellite receiver domain, which more traditionally supports TS. However, this could be balanced by the fact that some STBs are powered by an Opera browser, which promotes the WebM standard (even though Opera on STBs only currently supports the H.264 codec).
  • There is also an issue with WebM caching, which can be tricky. It can only be done using dedicated IP streaming servers. It can?t be done using web caches.
  • Officially, WebM does not mention DRM systems. However Matroska can support encryption very easily, even if DRM-enabled .mkv files are not very common yet.

Microsoft Silverlight Smooth Streaming

Smooth Streaming is part of Silverlight 3.0, and its specifications were published by Microsoft in September 2009. Video streaming was a major advance in Silverlight?s capabilities.

Smooth Streaming is based on fragmented files, with a PIFF (Protected Interoperable File Format) container, which is extended from 3gp format, and an underlying SSTP (Smooth Streaming Transport Protocol) layer.?The general principle is quite similar to HLS streaming:

  • Encode video in H264 and audio in AAC (or VC-1/WMA), in different bitrates;
  • Use a stream segmenter to generate fragments and mux them into a PIFF container;
  • Distribute through a HTTP web server, and provide appropriate caching.

The client software starts by requesting a manifest from the server. The manifest response from the server lists the available media, tracks and bitrates. The client then asks for one or more fragments corresponding to the requirements on the list to be sent by the streaming server over HTTP. Like HLS, when using Smooth Streaming it is the client that manages the choice of adaptive bitrate. Finally, it should also be noted that DRM are particularly well integrated into Smooth Streaming, with the possibility to use several DRM layers in the same file.

  • The general design principles for Smooth Streaming are quite similar to those of HLS and so, like the Apple solution, it provides easy adaptive bitrate management from the client side.
  • Contrary to the other two OTT systems, DRM is already well integrated in Smooth Streaming.
  • In the web streaming field, Microsoft Smooth Streaming has acquired a strong image gained from successful live HD (720p/1080p) streaming of major events. The video quality of the live broadcasting was praised, compared to that provided by Flash-based sites at the same time.
  • Microsoft specifications are very detailed, so solution support takes much more time to implement. The result is that Smooth Streaming may not be adopted as fast as HLS, which was designed as an easy derivation from the TS standard.
  • Although Smooth Streaming was clearly designed for web streaming, the player is always managed through the Silverlight plugin. Even Microsoft?s Internet Explorer requires the external plugin. Also, although Silverlight is officially supported on Microsoft Windows and Apple MacOS X, it is not the case for Linux workstations, or mobile devices. So Smooth Streaming cannot be used on any of the highly popular iOS devices (Apple iPhones, iPads, iPods...) or on Android platforms. For Linux OS, the solution is to use Moonlight, an open-source implementation compatible with Silverlight, based on the Mono framework.
  • Like HLS, Smooth Streaming is also limited by the fact that it is impossible to manage bandwidth from a centralized point on the network: everything is decided solely by the device clients.
  • Finally, Smooth Streaming is based on patented audio and video codecs, so its use may be subject to license fees, payable to MPEG LA or Microsoft.

Obviously, all three approaches have their advantages and drawbacks. The real question is: What are you going to use OTT for? Do you plan to launch an iPhone app? Or a corporate web site? Or a mobile service?... And do you want to include connected TVs? Or are you planning a new service with a dedicated set top box, created from scratch?? This will give you a starting point for your choice of a possible solution or solutions.?


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