Media Streaming Techniques

Media Streaming TechniquesChapter 7 Media Streaming and retentivenesshouseIn this chapter, we learn about media pullulateing techniques and emblematic gismos wontd within streaming. Streaming is the dish out of media delivery via calculating machine lucres, n archaean notably the net.Learning OutcomesTo explain streaming and how media is convey via information processing system networksTo demote an outline of the convert and store of flick material.Media Streaming is the process of transmission system audio frequency recording frequency and video signals via computer networks, most notably the net profit. It requires three parts, a source (to encode the stream), a legion (to host the streaming service), and a browser or player (to view the stream).Streaming is an increasingly serious technology to learn about as nub continues to be delivered to a variety of internet relateed winds.Internet communications protocol Television (IPTV) is effectively streami ng programmes (both TV and wireless) and movies over the internet instead of terrestrial transfer. The media streamed whitethorn be live (e.g. news) or on-demand (e.g. movies, programmes etc.). IPTV is usually over a un open up or subscriber network e.g. VirginTV (UK) with a specified minimum spirit of Service. This should not be conf apply with Internet TV (a.k.a. Web TV) which is transmitted exploitation the selfsame(prenominal) protocols save primarily consumed via a weather vane-browser on the open internet (eg. BBC iPlayer).7.1 Stream Creation7.1.1 CaptureThe media stream fuck be pre-recorded or a live feed that is getd and run by means of an encoder. An audio live feed squeeze out be used for internet radio it requires a sound instrument panel to capture the audio gossip. Sound capture finesses can be internal (eg sound cards or intact computer mformer(a)board device) or external devices (e.g. audio interface) though it would be novel to review the earlier chap ter on professional versus domestic signal levels earlier assuming that a built-in motherboard can handle your incoming audio signal. Similarly, live video is via a camera (webcam poor quality, or video camera higher quality) but the capture device is typically by video capture cards, IEEE 1394 inter-group communication (aka Firewire) or for domestic quality, a USB device. some(prenominal) USB plug-in devices carry both audio and video signals it is the softw ar in the encoder that is discipline to look for where the feeds ar attached to the computer.Current tablet and smart-ph stars can be used as internet streaming devices. These, along with some cameras, argon al depicty cloud connected for computer stock and sharing while IP-Cameras (viewable and governable on streaming sites) can be used for home security measure etc. It is possible that these provide become more ubiquitous and take aim greater streaming functionality in the future.7.1.2 EncodingEncoding is performe d by an encoding software system package such as Adobe Flash bide Media Encoder. A live feed or pre-recorded media must(prenominal) be taut and fed into the stream at a suitable moment ramble and in a format with which the media emcee can cope for the purposes of experience and re-direction. It is necessary for any audio video compression process to feel the right decompressor at the play-out destination. Compression ( opus- esteem reduction) at the transmission end can be in either one or two puff encoding and at a constant instant footstep (CBR) or variable moment rate (VBR).Live encoding must be done in real-time on-the-fly so it is a one gag encoding i.e. the image selective information is analysed and compressed once. Pre-recorded info can be a multi-pass (usually two-pass) process so the quality of the encoding is higher, but is not used in live stream encoding.Constant bit rate (CBR) is used for media streaming as the encoding quality and feed to the innkeepe r remains at the same bit rate, so can be at the maximum level the process bequeath al moo. Variable bit rate (VBR) is controlled by the bit rate range (Minimum Maximum) or the sightly bit rate ( all(prenominal)(prenominal) pass is averaged, and hence several averages are re-averaged) to light upon a close to uniform bit rate for the stream. Variable bit rate is used for a multi-pass encoding process.7.2 Network Connectivity7.2.1 IP cope (Internet Protocol terminus)Every computer device that can be connected to the internet requires a unique computer send for so that it can be make, rather equivalent a telephone number. So to host a media stream that can be found on the internet, the media waiter requires a static IP address. Like telephone numbers in a directory, IP addresses are convertible to meaningful names by a Domain Name Server (DNS) process running on a web-hosting server. hence media servers and web-servers are closely coupled, and media is capable of univer se found using a web- found URL (Uniform Resource Locator) such as www.youtube.com.The source device (the computer or IP enabled camera etc.) necessarily to be found by the media server. This gist the device has to join the media servers network (a more permanent linkup) or pass on its IP address for the session (a temporary connection lasting until the session ends).Network RouterThe yoke among the source device and the media server whitethorn not be a direct connection, but may run through other connecting devices (network servers and routers). A router is a device that redirects data to some other connected device either on its own or another(prenominal) network. This is basically how the interconnectivity of the internet works, routing between the server acting as the source devices internet service provider to other networks and finally organism re-directed to the destination.Multiplexer (MUX) plainly it would be inefficient if the stream of data being passed to a media server is solely dedicated to one source device. This is a poor use of bandwidth, (bandwidth being the range of frequencies available in the data stream), so fivefold devices are streamed simultaneously. A multiplexer (MUX) is a device that is used to combine input streams into a single output stream which is then(prenominal) split hold into individual streams using a de-multiplexer (DEMUX).Figure 7-1 Multiplexer to Demultiplexer7.2.2 Web-Host ServersFor a stream to be found it must be make available to web-browsers or stand-alone players (e.g. Windows Media Centre). The web-host server handles the web-site connectivity but need not be the same computer as the media server but both need a connection between them that isnt prone to interruption. This web site often has a web page (HTML HyperText Markup Language) with a plug-in media player connected to the media stream being managed by the media server, and contains the web-site in which the page resides. Consequently it must lin k to the internet and Domain Name Server process to resolve the IP Address from the web-site name, so the routing can direct the end users browser to the host.Figure 7-2 Connection diagramThe browser tho needs to connect to the internet via its Internet Service provider to link to the media streams web-host server (see figure 7-2 Connection diagram). Hence any internet device with media playing capability could view the stream including smart-phones, tablets and PCs providing it has the right decompressing codec and can manage the bit rate of the stream from the media server. This is why it is important to tender various streams of differing quality, bit rate and formats (e.g. a Windows Media Video .WMV format blame may not play on an iPad without a conversion app).A further file often created at the time of the stream hosting web page is an announcement file. These are particularly important to make likely viewers aware of the content and set links to the media stream.Podcast and VodcastPodcasts are audio files that are available for download from a web hosting service (vodcasts are video inclusive podcasts) and differ from media steaming in so lots as the content is downloaded then play on the users device. Streamed media is viewable but not downloaded to the device. They are often announced by RSS feeds (a short web content file) to which your device has been connected.7.3 Media Streaming ServersA Media server is supererogatory software that runs on a typical web server (or file server with web-host server connection). It requires a static IP so its address does not alter on each session). The media server software needs to add additional protocols to those found on a wide web-server. In addition to Hypertext Transfer Protocol (HTTP) which is inbuilt with the web server, these additional protocols differ for proprietary server software. Real Time Messaging Protocol (RTMP) is for Adobe Flash systems along with HTTP Dynamic Streaming (HDS). Microsoft Media Services (MMS) is no longer supported for windows streaming and now uses HTTP and Real time go Protocol (RTSP), and finally in that location is an HTTP Live Streaming (HLS) protocol which is for orchard apple tree iOS based systems.Adaptive streaming (HDS, HLS and Microsoft Smooth Streaming) requires the stream to be disunited (which is how HTTP delivers content) and may utilise the MPEG-DASH codec. Adaptive streaming is where the content is streamed as fragments in a variety of bit range with the computer automatically selecting the coterminous most enamor sized fragment based on its legitimate playback state to minimise buffering. This differs from the senior method of providing different dedicated streams at constant bit rates and the client selecting one most appropriate to their computers (or routers) connection capability.7.3.1Content DeliveryUnicastIn a Unicast scenario the client connects to the server on a one-to-one basis. The number of clients is limited by bandwidth considerations.MulticastIn a multicast scenario the server streams to a multicast IP address (this is a special address on the clients network). This is a one-to- umteen basis and is an effective means of reaching many clients with less bandwidth overhead.UDP v TCPAll content (including streams) is delivered across a network in packets. In User Datagram Protocol(UDP) the stream is sent without guaranteeing the connection and no acknowledgement of receipt is made. UDP is seen as fallible but it is simpler and quicker. Transmission Control Protocol (TCP) is bi-directional so will check for receipt and retransmit missing packets. TCP is seen as reliable but bumper-to-bumper. A good discussion on this is at http//en.wikipedia.org/wiki/User_Datagram_ProtocolComparison_of_UDP_and_TCP7.3.2Live StreamingA live stream needs to be seen at the time of broadcast. A live stream needs connection to a publishing baksheesh on the media server which connects to an encoding device. This may be another computer or a camera with IP addressable capability. The publishing foreshadow provides the connection between the content (live stream or pre-recorded) and the clients computer which links to it via a web-host request from the internet.7.3.3 Video on bring (VoD)If the stream is recorded then it is treatable in the same way as any pre-recorded media file. Note, it is not advisable to record an encoded stream and then re-encode it as this would severely compromise its quality.Streams and PlaylistsMedia streaming servers can have many pre-recorded files ready for streaming, often collected into separate playlists (one media file plays immediately afterwards another). These playlist or file streams can be on a continuous loop, or awaiting selection by a viewer through the browser. This latter selection method is called videoon-demand, although it equally applies to audio files as well.Bandwidth considerationsA media server can manage several streams and be cogitate to several web-hosts at the same time. This requires careful planning of the number of streams the media server can handle which is a function of its bandwidth connection. The more simultaneous streams being handled then the less the size of the bit rate is available for each of those streams. If a media server has a 1Gbit/second connection then it could notwithstanding handle 1000 x 1Mbit/second streams. However, full utilization of the bandwidth like this is not normally done there are recommended bit rates for video streams based on destination image size and manifestation ratio, e.g. a 1280* 720 HD video with stereo audio will require about a 2.5 Mbit/sec rate. A good source for this ishttp//www.adobe.com/devnet/adobe-media-server/articles/dynstream_live/popup.htmlPush blowThe relationship between the encoding source device and the media server is based on which device initiates the stream. i.e. it is PULLED from the source device by the media server (needed for video-on-de mand), or it is PUSHED to the server by the source device to start the service (a broadcast need). The media server needs to know how the stream is to be initiated for it to start the service.7.4 Storage7.4.1 Read Write facilitateAll devices that are used to store data (including audio and video) need to be able to draw up to the entrepot device high-speed than the transmitted data is fed to it, otherwise it must buffer (temporary memory store on a faster device) and then read from the buffer to maintain the data transmission sequence. Consequently if a device is used that cannot cope with the data transmission rate than it will fail or lose data e.g. using a low sieve SD card in a camcorder.Data is written to storage devices and stored in a binary format but unlike data transmission the Kilo/Mega/Giga/Terra sizes are based on multiples of 1024 (210) not 1000. The speed of data being read from a storage device may be muffleder than required to play in real-time which would w ill in its being prone to stutter and freeze.7.4.2 Simple Storage Devices ConsiderationsTapes early tapes (DVCAM, DV) required mark. This was to put a continuous time code on the tape before recording however later tape devices (including mini-DV camcorders) made this unnecessary, though any discontinuities or repetitions in the timecode could cause problems when ingesting material to an edit workstation.Cards cards such as SDHC have a class rating which will denote the read/write speed of the card in Megabits per second, and storage size in Gigabytes. Always check to check up on the card will work with the device and check to see if there is a device firmware update, particularly if the device is more than a year old.USB sticks as with cards their read write speeds differ wildly check using an on-line speed testing application, it is usually split up to transfer video files to a hard disc before using the file for playback or editing.CD and DVD turns have a read/write sp eed depending on the quality of the platter (recording speed), but another consideration is the data rate used in the writing process from such software as the video non-linear editor (NLE). An average bit rate (based on Peak and minimum Variable bit rate (VBR)) or constant bit rate (CBR) needs to be selected, that will not only write to the disk but allow the disk to be played on the output device. Computers can write to disks good at 9 11 Megabits per sec. But this needs to be slower (around 5 Mb per sec) if writing to a DVD that is to be played on an older standard-definition DVD player. You should consider the bit rate as part of your consideration of overall file size and the storage condenser on the disk. A good explanation of data rate count is given in-https//helpx.adobe.com/encore/using/project-planning.htmlbit_budgetingHard Disks Many older hard disks (often found in laptops) spin at 5400 rpm, this is too slow for video playback and a minimum 7200 rpm disk is needed . Hard disk read write at around 50-150 Mbytes per sec.SSD Solid State Disks are now finding favour due to faster read/write speeds than traditional hard disk technology. SSD read write speed is between 200-500 Megabytes per sec.7.4.3 Network StorageConnection speedAny network storage has to pass data via the network card (NIC network Interface Controller), this needs to be as fast as possible (preferably a character connection of 1Gbits per sec but a minimum of 10 Mbs for Ethernet). dissimilar other storage considerations network traffic can be bandwidth throttled (i.e. the bit rate is reduced) and will affect speed. If the NIC card is under your administration always set it on maximum performance.NAS, SAN, CloudNAS (Network Attached Storage) is what most slew think of as network storage- an array of hard disks that allows for file storage remotely from your computer directly accessible via the network.SAN (Storage Area Networks) are a separate network but pretty much do the same job as NAS differing in access protocol.The Cloud is just another remote storage area (uses SAN technology) but accessed via the internet (typified by a URL connection Uniform Resource Locator) not a topical anesthetic area network LAN connection (typified by a UNC connection Universal Naming Convention).7.4.4 burst wear (Redundant Array of Independent (or inexpensive) Disks) allows the disk storage to have a measure of tediousness and/or striping to create a secure method of retrieving data should there be a disk failure. For media technology only a few RAID levels (configurations) are used (i.e. Levels 0 and 5 see figure 7-3 Raid diagram).Level 0 usually this requires at least two disks and the data is striped across them. (Note It can be put on one physical disk using two logical drives but with littler advantage). That essentially means data is split into blocks and distributed across the disks. Typically used in video storage applications as it is fast, there is no periphrasis (no duplication) so recovery from a disk crash is almost impossible. Consequently if a disk fails then the file may not be fully recoverable. If you have RAID 0 on your disks, always be sure to keep an external copy of your original audio or video files.Level 1 disk mirroring, requires at least 2 disks but is slow as it writes the same data twice (once to each disk). Data is easy to recover as the system has full redundancy (disk duplicated). This level is good for general data and possibly audio only files. Many video editors feel this level is too slow for workings with video files.Level 5 block striping and similarity. This requires 3 disks minimum, data is striped across all the disks (except one) and the block parity is put on the excepted disk. This is done repeatedly using a different disk for parity on each block. One disk can fail and be rebuilt from the others by using the parity blocks on remaining disks. Raid 5 is also popular with video editors as lo ng as the rupture controller is fast enough. It is slower than level 0 but faster than Level 1 and has enough redundancy for disk recovery.