Making Sense of Video Streaming Protocols
`
`linkedin.com/pulse/making-sense-video-streaming-protocols-dr-brijesh-kumar/
`
`Brijesh Kumar, Ph.D.
`CTO & CPO - Software / Cloud Engineering, Business, Products & Market Strategy: Cloud Digital
`Transformations/ Data Strategy, IP/ Cellular Wireless/ SaaS Products, IT Security and Software Technology
`
`15 articles
`August 11, 2015
`
`In my previous article – “Making Sense of Video Streaming Formats”, I discussed various video streaming
`formats and their differences. Before you plan for broadcasting videos, or preparing video streams for
`streaming, it is important that you understand various video container formats. As a matter of fact, half the
`mystique in video streaming is knowing which video format to use to create, store and broadcast, and other
`half is in using the right streaming protocol and proper media streaming server.
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`Choosing correct streaming protocol is important because it will determine what kind of devices it will play
`on, quality of videos and whether you would need specially created video player or not for those streams.
`For example, standard format for Adobe Media Server is RTMP stream. However, RTMP stream is not
`natively supported by Apple iOS since Steve Jobs rightly determined that Flash is not designed for mobile
`devices as it consumes too much power and is unsafe. You can read the very persuasive and readable note
`from Steve Jobs himself on Apple's website (http://www.apple.com/hotnews/thoughts-on-flash/).
`
`At the outset, it is important to understand the differences between various terms used in video streaming
`industry.
`
`In this article, we will discuss video streaming protocols, and their differences.
`
`1. Understanding Different Streaming Methods
`As I previously mentioned there are two ways to serve video contents downloading and streaming.
`
`A. Download and Play
`
`The simplest way is to let user download an entire file by simply embedding the video-link in the contents.
`However, we all know the drawback of this approach. Video files sizes are large and hence, it may take a
`while before a user can view the file. If the file is quite small and limited just to a few megabytes, this may
`not be too much of an inconvenience, but for large video files like movies or class lectures that can be in
`gigabytes, it can be very off-putting. On the positive side, you can instantly fast forward or reverse the play
`point during playback to any point of interest simply by clicking on local player's progress bar.
`
`B. Streaming Videos or Video of Live Events
`
`Streaming media works a bit differently — the end user can start watching the file almost as soon as it
`begins downloading. In effect, the file is sent to the user in a (more or less) constant stream, and the user
`watches it as it arrives. The obvious advantage with this method is that no waiting is involved. Streaming
`media has additional advantages such as being able to broadcast live events (sometimes referred to as a
`webcast or web streaming).
`
`In streaming, a client media player can begin playing the data (such as a movie) before the entire file has
`been transmitted. Live streaming, which refers to content delivered live over the Internet, requires a form of
`source media (e.g. a video camera, an audio interface, screen capture software), an encoder to digitize the
`content, a media publisher, and a content distribution network (CDN) to distribute and deliver the content.
`This is in contrast to downloading an entire file and playing it.
`
`True streaming video must be delivered from a specialized streaming server as Adobe Media or Red 5
`Media server. Delivering content over protocol RTMP is called “streaming”. The client creates a socket
`connection to the server (such as Adobe Media Server) over which the content is sent in a continuous
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`stream. The client can seek to any point in the content instantly, regardless of how much data has been
`transferred.
`
`One major benefit of using streaming server is that you can use the adaptive rate control. This means that
`the rate of transfer will automatically change in response to the transfer conditions. If the receiver is not able
`to keep up with a higher data rate, the sender will drop to a lower data rate and quality. This may be done by
`changes within the stream, or by switching the client to a different stream, possibly from another server
`
`C. Progressive Downloading
`
`There is also a hybrid method known as progressive download. The content must transfer from the server to
`the client in a progression from the beginning to the end of a file. A client cannot seek to a forward location
`until that location and all the data before it has downloaded. In this method, the video clip is downloaded but
`it begins playing as soon as a portion of the file has been received. This simulates true streaming, but does
`not have all the advantages.
`
`One major drawback of progressive streaming is that it cannot do rate adaptive transmission like a true
`streaming server can. In the days of high bandwidth links, it is not a problem, but if you are in low bandwidth
`area, the limitations become quite obvious.
`
`YouTube is a prime example of progressive streaming over http.
`
`1. Challenges of Setting Scalable Streaming Infrastructure
`
`With the exception of watching live events, what we mostly consume is on-demand streaming. Videos are
`kept in proper format suitable for streaming on the servers. If users have uploaded these videos then videos
`are encoded using dedicated encoding servers or encoders. Video encoding is a very compute intensive
`process since all frames of audio and video must be processed and re-packaged in new formats. A provider
`must provision enough number of servers to do encoding and the serving of these videos.
`
`Two popular software for video encoding are FFMPEG and LAME. I have used them to handle most of
`video encoding needs for clients. You can add any cloud based systems such as Amazon EC2 stack so that
`you can scale your encoding needs as demand grows up.
`
`Video streaming companies often use a Content Distribution Network (CDN) or build their own distributed
`multi-location serving infrastructure.
`
`Live streaming on the other hand uses a live video encoder and that a video stream is then attached to a
`video streaming server. There are many video streaming servers such as Adobe Media Server (AMS), Red 5
`or Wowza are available. Since one server can only serve limited number of streams simultaneously, multiple
`servers must be provisioned in a chain. Failure to provide enough capacity will result in its inability to serve
`stream in real-time resulting in very unsatisfactory results for all.
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`Streaming servers commonly support more than one protocol, falling back on alternatives if the first choice
`does not work.
`
`1. Main Streaming Protocols
`
`.There are a number of streaming protocols currently available. A typical media server will support multiple
`streaming protocols and you can configure whatever is needed.
`
`In addition, one needs to understand that the support for the right streaming protocol does not necessarily
`mean that a recipient device is capable of playing a particular stream. You need support of streaming
`protocol as well as support of appropriate streaming protocol.
`
`A. The RTP Family
`
`The Real-time Transport Protocol (RTP) is a network protocol for delivering audio and video over IP
`networks. RTP is designed for end-to-end, real-time, transfer of streaming media. RTP is used extensively in
`communication and entertainment systems that involve streaming media, such as telephony, video
`teleconference applications, television services, and web-based push-to-talk features.
`
`RTP is used in conjunction with the RTP Control Protocol (RTCP) and the Real Time Streaming Protocol
`(RTSP). While RTP carries the media streams (e.g., audio and video), RTCP is used to monitor transmission
`statistics and quality of service (QoS) and aids synchronization of multiple streams. RTP is one of the
`technical foundations of Voice over IP and in this context is often used in conjunction with a signaling
`protocol such as the Session Initiation Protocol (SIP), which establishes connections across the network.
`
`The Real Time Streaming Protocol (RTSP) is designed to control streaming media servers. The protocol is
`used for establishing and controlling media sessions between end points. Clients of media servers issue
`VCR-style commands, such as play and pause, to facilitate real-time control of playback of media files from
`the server.
`
`RTP, RTCP, and RTSP were standardized in various goups in IETF. They all operate on different ports.
`Usually when RTP is on port N, RTCP is on port N+1.
`
`Android and iOS devices do not have RTP-compatible players as delivered. There are various third-party
`applications, including RealPlayer for Android.
`
`B. RTMP from Adobe
`
`Real Time Messaging Protocol (RTMP) is a proprietary protocol developed by Adobe and used primarily by
`Flash. RTMP provides bidirectional message multiplex service over a reliable stream transport, such as TCP,
`intended to carry parallel streams of video, audio, and data messages, with associated timing information,
`between a pair of communicating peers.
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`RTMP is a system for delivering on-demand and live media to Adobe Flash applications (like the JW Player).
`RTMP supports video in MP4 and FLV and audio in AAC and MP3.
`
`RTMP decoder is primarily used in live stream broadcast though the use of RTMP will decline with the
`decline of Flash. The RTMP can do dynamic streaming, where the video quality automatically adjusts to
`changes in bandwidth.
`
`RTMP can be tunneled through HTTP (RTMPT), which may allow it to be used behind firewalls where
`straight RTMP is blocked. Other variants are RTMPE (with lightweight encryption), RTMPTE (tunneling and
`lightweight encryption), and RTMPS (encrypted over SSL).
`
`Apple's iOS does not support RTMP or Flash, so iPhones, iPods, and iPads will not accept RTMP streams
`except through third-party code. Some RTMP implementations (e.g., JW Player) rely on the availability of the
`Flash plugins. New HTTP streaming protocols, like Apple's HTTP Live Streaming (HLS), have wider device
`support (e.g. iOS) and will likely replace RTMP over the coming years.
`
`C. Apple's HTTP Live Streaming (HLS)
`
`As I mentioned earlier, Apple never liked RTMP or Flash, and came with its own solution to implement video
`streaming on its popular iPhone, iPAD devices.
`
`HTTP Live Streaming (also known as HLS) is an HTTP-based media streaming communications protocol
`implemented by Apple Inc. as part of its QuickTime, Safari, OS X, and iOS software.
`
`It works by breaking the overall stream into a sequence of small HTTP-based file downloads, each download
`loading one short chunk of an overall potentially unbounded transport stream. As the stream is played, the
`client may select from a number of different alternate streams containing the same material encoded at a
`variety of data rates, allowing the streaming session to adapt to the available data rate. At the start of the
`streaming session, it downloads an extended M3U playlist containing the metadata for the various sub-
`streams, which are available.
`
`In general, you can use FFPEG software to convert RTMP stream to HLS stream. HLS is widely supported in
`streaming servers from vendors like Adobe, Microsoft, RealNetworks, and Wowza, as well as real time
`transmuxing functions in distribution platforms like those from Akamai. The popularity of iOS devices and this
`distribution-related technology support has also led to increased support on the player side, most notably
`from Google in Android 3.0 onward.
`
`D. HTTP Dynamic Streaming (HDS) By Adobe
`
`HTTP Dynamic Streaming (HDS) was developed by Adobe as an alternative to their RTMP protocol. HDS
`allows for adaptive streaming over HTTP to any device that’s compatible with Adobe Flash or Adobe Air. A
`big benefit to streaming with HDS instead of RTMP is not having to rely on an Adobe Flash Media Server
`(FMS), which significantly decreases the cost of operating the stream. Adobe has released a module for
`Apache, the most popular Open Source HTTP server, which allows it to act as a streaming origin server.
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`Because the Flash Player is not supported by Android and iOS, which limits practical use for broadcasting to
`mobile devices. Given a choice, using HLS stream is a better option.
`
`E. Microsoft's Smooth Streaming
`
`Smooth Streaming is Microsoft's entry in the very fragmented world of HTTP streaming. It is used with
`Silverlight and IIS Web Server. Streaming to Apple devices is possible when using the H.264 video codec.
`IIS is able to transmux HSS fragments into ones compatible with iOS 3.0 and later devices.
`
`F. HTML 5 Streaming
`
`In addition to the various protocols, you can stream your media using HTML 5. Most modern web browsers
`and even mobile phone browsers can stream audio and video with HTML 5.
`
`However, not every browser can play the same file. Therefore, you have to offer different formats of the
`same file in order to reach the wider audience. For audio, you can use .mp3 and .ogg, and for video we can
`use .mp4, .ogv, and .webm.
`
`The embedding HTML5 Video support in the pages is very easy. All it needs is a few lines of the code as
`given below:
`
`Sample code:
`
`<video width="356" height="200" controls poster="path/file.png" >
`
`<source src="path-to-video/file.mp4" type="video/mp4" />
`
`<source src="path-to-video/file.ogv" type="video/ogg" />
`
`<source src=" path-to-video/file.wbem" type="video/webm" />
`
`<em>Sorry, your browser does not support HTML5 video.</em>
`
`</video>
`
`1. Summary
`
`In this article, I discussed various current protocols and methods for video streaming. There are so many
`choices on servers, protocols, and formats. It is not easy to select a method unless you know all the options.
`The understanding of video streaming formats and protocols will help you plan accordingly.
`
`If you need more help in setting large-scale video streaming infrastructure for mobile or desktop devices, feel
`free to contact me for suitable advice.
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`Published by
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`Brijesh Kumar, Ph.D.
`Published • 8y
`
`15 articles
`
`7/7
`
`Sportradar 1028
`Page 7
`
`