Ensure Video Quality in Your Mobile Delivery

Oct 2, 2009 3:58 PM, Marwan Jabri, Founder and CTO, Dilithium Networks

Though mobile devices are becoming more sophisticated, with more processing power and better usability, providing video across multiple platforms remains a challenge.

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Provided by 3G, HSDPA, and Long-Term Evolution (LTE), the boost in bandwidth availability is fueling the rise in mobile video access from handsets and netbooks. Larger screens, advances in compression technologies, flat-rate data-access charges, and more efficient and improved quality media adaptation technologies also are driving mobile video access growth.

Variations across mobile screens, netbooks, and handsets dictate the adaptation of entertainment content as terminals typically vary in screen size, network access bandwidth, and media/codec processing and protocol capabilities. The conversion from one format to another is accomplished in real time or in an offline mode depending on the use case.

Marwan Jabri brings nearly 20 years of research and development expertise in multimedia communications systems and intelligent signal processing. He has significant expertise in media communications protocols, and he was closely involved with the ITU in the development of the ITU H.324/H.324M standards. He was also founder of the Systems Engineering and Design Automation Laboratory (SEDAL) at University of Sydney and was awarded the Outstanding Young Investigator Medal by the Australian Telecommunication and Electronics Research Board.

For example, a content asset may be available in an MPEG2 transport stream (MPEG2TS) file format and require delivery to a netbook user connected over a 3.5G mobile network with an Adobe Flash player. The video format in the original stream may be in MPEG2 video and Dolby AC3 audio. Delivering this content for best viewing on the consumer’s netbook with the Adobe Flash player would necessitate the following conversions:

• MPEG2TS to Flash video format (FLV)

• MPEG2 video to H.264 AVC

• AC3 audio to AAC

• Bandwidth from a high bit rate of 1 to 6 Mbits/s to few hundred kbits/s

• Screen size from HD (1080i/p, 720i/p) or SD/ED (480i/p) to VGA, HVGA, or QVGA

• And possibly the frame rate from 30 f/s to around 20 f/s

If the netbook consumer uses the Microsoft Windows media player, the container format would have to be Microsoft’s Windows Media with Microsoft’s Windows Media audio/video codecs.

Essential Media Adaptation

Depending on the use case, the media adaptation will need to be performed on demand in real time or in an offline (batch) mode. The most basic operation of media adaptation is video scaling, encoding or transcoding, frame-rate, and bit-rate adaptation.

If video codecs are defined by standards, how can one encoder be superior to another? Standards define valid bitstream structures and decoders, but not encoders or encoding strategies. So as long as compressed video bitstreams comply with the specification, the standard has served its purpose.

As an example, most modern video standards use a motion prediction tool. Motion prediction is usually about determining whether a portion of a video frame (e.g., a 16- by 16-pixel 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.