Application Needs: Mobile
The New Market for Video
In an increasingly mobile society, the fastest growing video market is video on mobile devices.
The latest generation of mobile phones, featuring bigger screens with higher resolutions, is more clearly targeted at video than any previous generation. MP3 audio players have evolved into MP3 video players, many with full-size touch screens. Both of these handheld market segments are still growing rapidly, driven in part by fierce completion between many different vendors
While the mobile phone and video MP3 player dominate the market for pocket-size handhelds, for image-oriented devices, there is also a rapidly developing demand for larger mobile screens. Apple’s new 9.7” screen iPad, an inexpensive, video-oriented slate computer, has been received with overwhelming enthusiasm. This emerging market segment soon will be populated with contenders from multiple companies. The new market for slates—moving down from the world of 12” LCD screen Tablet computers—threatens to collide (or merge) with the upward growth of another rapidly growing market segment, the 6” screen eBook reader, as e ink devices add color and video capabilities over the next few years.
Intermediate-sized hybrid or cross-over devices, typically featuring screens in the 5-7 inch range, also command their share of attention. These systems typically combine aspects of a mobile phone with a tablet computer and a netbook.
Even in the older personal computer market, the fastest growing segments are the most highly mobile segments, namely small Netbooks, with 7-10 inch screens, and Ultra-portables, with 11-13 inch screens. Among larger, full-featured systems, portable notebooks with screens in the 14-17 inch range outsell traditional desktop computers (and larger “luggable” notebooks) by a wide margin.
Requirements for Mobile Encoding
Encoding for a full-featured notebook computer may be indistinguishable from HD broadcast encoding. However, as screen sizes shrink and functional capabilities dwindle, moving down along the path from a 7 pound notebook computer with a 17 inch screen to a 1 ounce Video Watch with a 1.5 inch screen, there are a number of considerations to take into account.
Screen Resolution: Large notebooks, with1920 x 1200 displays (16:10 WUXGA), offer full 1920 x 1080 (16:9) HD resolution. From WUXGA, mobile resolutions range across a truly formidable spectrum of possibilities. The following list is a sample of some of the more common resolutions encountered on screens of diminishing size.
- 1024 x 768 on the 9.7” screen of the iPad
- 960 x 640 on the 3.5” screen of the iPhone 4
- 640 x 480 on the 5” screen of the HTC Advantage x7510
- 480 x 320 on the 3.5” screen of the iPod Touch
- 320 x 240 on the 2.46” screen of the Blackberry Curve 8530
- 220 x 176 on the 1.9” screen of the Sandisk Sansa Fuze Video MP3 player
- 128 x 128 on the 1.5” screen of the Video Watch
A mobile video encoder must have the flexibility to accommodate any of these and other target resolutions, depending on the requirements of each customer.
Encoding Profile: The capabilities of a mobile encoder must be matched to the capabilities of mobile decoders. Some devices support Main profile, with both progressive and backward references, plus advanced CABAC entropy encoding. Other devices support the simpler Baseline profile, with progressive references only and less aggressive CAVLC entropy encoding. Again, a mobile encoder must have the flexibility to adjust to the capabilities of its target decoder.
Audio Codec: A mobile decoder also may support only a specific audio codec, for example MPEG-1, Layer 2 or AAC. Again, a mobile encoder must have the flexibility to provide audio encoding compatible with the audio decoding capabilities of the mobile device.
Bit Rate: In addition to restricted decode capabilities, mobile devices generally have limited bandwidth and storage space. For video on demand, highly compressed files download more quickly and take up less storage space. For live streaming over a wireless network, the lower the bandwidth, the less likely video is to stutter, skip or freeze during play-out. Consequently, the ability of an encoder to provide highly compressed video, frequently below 1Mbps, can be vitally important. Similarly, the ability of an encoder to support highly compressed audio codecs like AAC-LC or HE-AAC can be a significant bit rate savings for mobile devices that can decode these formats.
Frame Rate: One way to effectively improve live streaming to mobile devices is to use a reduced frame rate. Although NTSC SD and 1080i HD television both use rates of 30 frames per second (fps) for interlaced video, film is traditionally shot at a lower 24fps rate—and even 24fps is higher than really necessary. The human eye will transform a succession of still images into the perception of smooth motion at any rate down to about 10fps. The eye’s willingness to accept low frame rates means the ability of an encoder to output reduced frame rates (compared to normal TV standards) can be an effective way to support live streaming of quality video on bandwidth-limited mobile devices. For 30fpps NTSC inputs, fps reductions of one-third (20fps), one-half (15fps), and even two-thirds (10fps) are useful. For 25fps PAL inputs, the corresponding reductions are one-fifth (20fps), two-fifths (15fps), and three-fifths (10fps).
Telairity Mobile Encoders
Telairity offers three different lines of encoders that support the mobile market, including universal HD/SD/Mobile BE8500 encoders and transcoders, high-compression 9000 Series SD/Mobile systems, and dedicated mobile-only 6000 Series encoders. Both 9000 Series and 6000 Series encoders are available in four-channel versions.
Since popular mobile targets are often incompatible in their resolutions, encoding profiles, audio codecs, and useable bit rates, multi-channel encoders that can accept a single input and simultaneously output multiple custom streams are often the best choice for mobile transmissions.
Maximum Versatility: The Universal BT8500 Transcoder can convert any type of input, HD or SD, 4:2:2 source over SDI or pre-encoded MPEG-2/MPEG-4 (etc.) over either ASI or IP, to any desired mobile output H.264 or AVS format. Transcoding, Transformating, Transrating, or Transscaling is performed as necessary to achieve the desired conversion. The BT8500 can also encode/transcode for all standard HD and SD formats. For customers that don’t need to convert pre-encoded sources to H.264 or AVS, the Universal BE8500 Encoder provides complete HD/SD/Mobile flexibility without the transcode capabilities of the BT8500.
Maximum Compression: For customers without HD encoding needs, the BE9110 high-compression SD/Mobile encoder provides the ability to output full SD formats under 1Mbps, and smaller mobile formats at rates as low as 100Kbps. For customers with multi-channel requirements, the BE9400 provides 4 9000 Series channels in a single 1U chassis. Each channel can accept a separate input, or all four channels can take the same input and format it for four different target devices.
Maximum Efficiency: The dedicated mobile-only BM6110 provides full input flexibility, accepting any HD or SD source, native or pre-encoded, but only outputs mobile baseline formats at bit rates from 128Kbps to 768Kbps. For customers with multi-channel requirements, the BM6400 provides 4 6000 Series channels in a single 1U chassis. Each channel can accept a separate input, or all four channels can take the same input and format it for four different target devices.