Mobile Versus Internet Streaming: 5 Key Challenges
It’s widely understood that competing vendors’ encoders produce different quality video and audio playback, because the standards concerned define the general codec technology but not the actual implementation. This means each vendor can optimise its own version, and the output quality will vary between competing encoders. Therefore, it is essential that an encoder gives the highest possible output quality and supports all the required media formats, in addition to offering advanced features relevant to mobile networks (such as error correction and data partitioning). A consideration at the content production stage is to use techniques sympathetic to viewing video on a small screen, such as to minimise the use of quick camera zooms and pans – there are many such techniques that can help produce the best quality content with minimal effort.
Mobile operators must deliver the highest quality streaming in the most efficient manner, taking into account the characteristics of the wireless network. Unlike the internet cases, the operators have complete control of the data flowing across their networks to the end-user devices. As such, it’s possible to optimise the streams based upon knowledge of how the various network components function. For example, traffic flow and smoothing algorithms in the core network (such as the gateway GPRS support node [GGSN] and serving GPRS support node [SGSN]) and streaming server can ensure a steady flow of data packets with minimal "spikes" or bursts, and the data packets can be delivered over special real-time (RT) radio channels with a suitable quality of service, rather than the ‘best effort’ non real-time radio channels invariably used today.
Additionally the radio network bandwidth should be used more effectively, physical radio channels being used based on the actual properties of the stream itself, i.e. it is more efficient to deliver a 12.2Kbps audio-only stream over a 16Kbps RT radio channel than a 64Kbps NRT channel. Operators are now beginning to deploy these methods as their existing streaming services mature and expand.
2. Fluctuations in the Wireless Network
When streaming over mobile networks, is it important to remember that the over-the-air bandwidth fluctuates depending on factors such as the prevailing network conditions and whether the user moves between cells. Most modern handsets have quite a limited buffer size and memory, so network issues are more readily observed in contrast with internet streaming.
Therefore, it’s advantageous to use a streaming server that can send the most appropriate bit-rate to the handset and can dynamically adapt the bit-rate to maximise quality (and eliminate annoying ‘freezes’ in playback), a term commonly referred to as Dynamic Bit-rate Adaptation (DBA). DBA techniques are fairly complex; each vendor implementation is different and some are much more effective than others.
DBA usually comes in two varieties with a distinction on where the bit-rate adaptation decisions are made: the first is implemented in the mobile player (which tells the server which bit-rate to send) and the other by the server. The latter case is possibly superior as it allows intelligent decisions to be made for all players, including those which do not have their own built-in DBA function. This is an important point because the majority of mobiles have no inherent rate-switching mechanism, so it is advantageous if the server can fulfil this task itself (or in conjunction with the player) based on universally-supported standards.
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