Operators' Struggle with Video On Demand
The advent of 3G and 4G has opened up the bandwidth for video-on-demand services, and consumers are taking advantage. This can be seen with Netflix's recent subscriber-base victory over Comcast, now supporting 23.6 million video content users. Netflix's critical differentiator is that it allows consumers to access video when it is convenient for them – on demand.
Entertainment like movies and TV shows will be the biggest driver for the adoption of video-on-demand services. However, there are several other avenues for growth that operators can take advantage of, such as news and sports channels, particularly for mobile device access. For example, 3G/4G on mobile devices allows a user to get faster football game updates, plus live TV streaming capabilities for better content and easier accessibility. Adoption of these services will be high since users can watch their favorite sport or the local news in real-time and at their convenience. Furthermore, mobile handsets with larger and more high-resolution screens, which are becoming increasingly available at more affordable prices, as well as flat-rate data access charges, will encourage a huge uptake in video-on-demand services.
As more and more consumers demand mobile video, operators will need to find a way to keep up. If they are able to satisfy consumer demand, the adoption of these services could be monumental for the telecom sector. It will enable operators to provide high transfer rates over longer distances and efficient bandwidth so their consumers can seamlessly watch any content at any time. Consumers also will be able to maximize the potential of GPS services, which are built into all smartphones today but are still dependent on the operators' network for efficiency, as well as multi-player gaming facilities. These capabilities lead to larger revenue opportunities and a higher level of customer satisfaction, both of which positively impact the bottom line.
There are many challenges associated with delivering mobile video content, however, and most operators are not equipped to handle them. First, since content must be delivered to all types of devices, it needs to be converted to fit different screen sizes, bandwidth constraints and media/codec processing and protocol capabilities. The conversion from one format to another usually involves several intricate steps. Secondly, there is the media adaption process, which is performed on-demand, in real-time or in an offline (batch) mode. The most basic operation of media adaptation is video encoding, transcoding and bitrate adaptation – all described below.
While video codecs are defined by standards, all encoders are not created equal. Standards define valid bitstream structures and decoders, but not encoders or encoding strategies. Therefore, as long as compressed video bitstreams are compliant to the specification, then the standard has served its purpose.
For example, most modern video standards make use of what is called a motion prediction tool. Motion prediction is typically about determining whether a portion of a video frame (e.g. a 16x16 pixels macroblock) is present in a previously encoded frame. If it is, then the amount of bits needed to encode that portion can be significantly reduced by reusing the portion. To do this, the encoders need to first determine the best matching block in an area surrounding the macroblock in the previous frame (motion estimation); then on the basis of that match, determine whether the macroblock is unchanged (encoder can skip) or some differences exist and can be encoded (the encoding of the differences will yield fewer bits than the encoding of the macroblock itself).
Each of these two steps can be implemented in various ways – some being more efficient (compute cycles and memory utilization) and others providing much greater quality. In fact, the second step can be invoked in a variety of ways according to an encoding strategy and the context of the application (i.e. constant versus variable bit-rate; offline-mode versus real-time transcoding; etc). Hence, when it comes to video quality, the adherence to a video standard is not a measure of quality.
Real-time or on-demand transcoding is challenging because the transcoder has to convert the media stream from one codec to another while maintaining appropriately short input to output latency. The transcoder does not have the benefit or luxury of multiple passes over the incoming bitstream in order to transcode while maintaining bandwidth efficiency using information from a time later in a clip. The real-time transcoder has to employ coding strategies that predict the changing bandwidth needs of video frames, and encode them accordingly. Failure to do so leads to highly variable video quality, and inefficient bandwidth utilization.
Dynamic Bit-rate Adaptation
While bandwidth variations are common in many networks, they are more severe in mobile and wireless networks. In today's 3G/4G networks, quality of service (QoS) is often shaky, and best effort approaches are used. For example, available bandwidth to a 3/3.5G user typically varies from 64kbps to 300kbps – these types of fluctuations in available bandwidth result in severe degradation to the customer experience.
Dynamic bit-rate adaptation (DBRA) is a general term used to describe the ability of a delivery system to adjust its transmitted bandwidth to match network fluctuations. DBRA approaches are different for RTSP and HTTP progressive download (PD). In RTSP, there is a standardized approach that is increasingly being adopted by infrastructure providers and handset vendors. For the RTSP DBRA scheme to be of value, handset support and the support of RTSP streaming and relay servers is essential. For HTTP PD, there is no standardized way today to implement DBRA. Different terminals and media-player technologies implement different strategies. Some, like the iPhone (iOS3 and beyond), require that a multiplicity of bitrates be listed in the content asset, and the decision of which one to select is left to the iPhone media player. Other streaming and media player technologies use different approaches.
Leveraging Value-Added Services for Video Content
These strategies for smart encoding, real-time transcoding and dynamic bit-rate adaptation are available today through value-added services (VAS) providers and should be taken advantage of by U.S. operators as their customers increasingly demand video content. VAS providers can provide these essential ingredients for scalable software-based deployments to help operators deliver a high quality customer experience at a reasonable cost.
Marwan Jabri is the vice president, Video Products Unit for OnMobile and is based in Petaluma, Calif.