Autor: Redaktion

Streaming Backpacks

A number of international news organisations make use of I.P connected; video streaming backpacks (such as TVU Networks, LiveU, QuickLink etc.) to transfer content back to the newsroom.

There are two different operating modes, Live mode or File transfer method (this is often referred to as Store and Forward) both of which make use of a compact mobile communication unit which transmits video signals in real time, via cellular mobile connections or alternative connectivity (such as Local Area Networks –LANs , and Wifi ). The transmissions are delivered to a receiving server at the broadcaster.

Most systems have an HD-SDI or HDMI input interface. A camera is connected to the backpack and allows for images and sound to be sent live, or delivered as files, back to base. In some systems progressive and interlaced SD / HD resolutions are accepted, including two embedded audio channels. From a signal processing perspective, the devices rely primarily on a real-time encoding system in the backpack, often using a H.264 codec.

Alternatively it’s also possible to transfer files via a USB port from external devices or via the integrated memory card slot using FTP transfers.

Some devices also have the ability to monitor what is going out on air as their systems come equipped with the functionality to provide a return channel for monitoring.

For transmissions that are not time critical, it is recommended to setup the streaming device to have a preference for quality, rather than have a shorter file transfer duration. However when dealing with live delivery it is important to achieve a balance of the lowest latency (time to deliver the signal), whilst maintaining the best quality images that the network connectivity will allow.

In order to gain as much bandwidth and stability as possible for the upload of data packets there are different points to consider, such as adaptive bit rate streaming (lowering the quality of the encoding when the connectivity bandwidth reduces), dynamic resolution adjustment, Forward Error Correction (FEC), and mobile/connectivity channel bonding.

The bandwidth available in any geographic location can vary greatly. This can depend on whether the connection is a 3G or 4G mobile signal, access provided via Wireless LANs or KA-Satellite via LAN. A mixture of these systems, where possible, will help to reduce packet (data) losses as the video data is divided dynamically across the different connections.

In streaming backpacks, video and audio data is sent as packets, divided across all the Internet connections used in the device. The combined signal is reassembled at the receiving server at the broadcaster or production facility. Due to the variety of different paths the data can take, and the resulting packet (data) delays, a faster processing time (low-latency) for real-time operation at the receiving end is necessary.

The latency is the time required to compensate for packet delay from the receiver to bring data packets back in the correct order (jitter) or if necessary, to request bad packets again. Taking into account all available connectivity options, modern streaming backpack systems can combine more than 10 different connectivity channels with each other. This can easily enable a target data connection rate of up to 10 Mbit/s and beyond.

If you are only using the device in mobile connectivity operation you should consider using multiple LTE / UMTS modems incl. SIM cards from different providers. This will provide the broadest possible coverage or availability by using different networks bonded together, and can also distribute the transmission data across multiple SIM cards. This ensures that within any mobile cell, the system is not limited by a single SIM, but can spread the load across multiple connections and networks. High performance backpack systems have up to eight integrated cellular modems; lower cost devices have fewer modems, but can be expanded by connecting external mobile dongles. Some manufacturers also offer external antennas for vehicle or tripod mounting.

Many systems now offer the ability to control and configure streaming servers remotely via a Web page interface, either within the broadcast facility or within the cloud (e.g. LU Central LiveU).

The delivery of video and audio signals to other systems within the broadcaster (e.g. vision mixer or playout system) can be assigned through the receiving servers’ HD-SDI Playout Channels or alternatively at the file level, using push processes to one or more FTP servers. Currently receiving servers can receive up to a maximum of four H.264 video streams simultaneously per server and, optionally, can then convert into a set target resolution (e.g. 1080i25). Receiving servers can be configured to distribute the received signals using the Point-to-multipoint method. This enables the signal to be sent to one point within a broadcaster, but distributed to multiple outlets at the same time.

For security reasons, the receiving server/decoder is usually in a separated network segment (called a De-militarised Zone or DMZ) and is connected with a fixed IP address on the public Internet. The majority of these services run on a customised Linux distribution.

In addition to the hardware solutions described above, there are purely software-based applications (streaming apps including: LiveU LU-Smart), from other manufacturers, which have similar functionalities and can deliver video to the same infrastructure. The article "News Reporter Apps" addresses it in more detail.

Due to the compactness, scalability, flexibility, low investment and transfer costs, streaming backpacks are used for delivering live feeds on a daily basis.

Streaming backpack and bonding devices have become essential for covering live events, however it is only possible with network connectivity – and with that comes a risk to the number of mobile or fixed connections that you can use. Productions should consider the impact that reduced connectivity will have on the amount of compression that will be applied to their video - as the lower the data connectivity rate, the lower the quality of the compressed video footage.

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