Producing Content for Mobile Delivery

Multiple factors determine encoding bitrate and bit optimization (where bits are allocated). The delivery channel likely has a maximum available bitrate, further limited by RF variability and headroom allocated to buffer variability. The playback device is limited by which codecs are supported and the power of the CPU processor used to perform the decoding. The content type and length also affect bitrate requirements. Dynamic action, for example, requires a higher bitrate to look good. Long run times may need less bitrate for small file sizes in a video-on-demand application.

Production
In order to effectively deliver video content to wireless and mobile users, content providers must move from an "MTV" mind-set to a narrowband mind-set. Every aspect of production needs to be examined from this viewpoint. Not all content will work well in narrowband. Preprocessing repurposed content for mobile delivery will reap significant benefits. The best scenario is to deliver content purposely designed to encode well for narrowband delivery. Whether repurposing or creating new content, be sure to return to the fundamentals of production:
• Rely on strong storytelling and well-composed shots.
• Place less emphasis on visual eye candy.
• Pace edits less frenetically.

The narrowband mind-set requires a shift in production values. First, the rate and amount of change should be carefully controlled. Both contribute significantly to higher bandwidth requirements. Second, a jump to a higher visual quality level is difficult to achieve. Instead, one must accumulate small improvements in each step of production. Therefore, no opportunity to improve quality is too small. Always choose the quality option. Do not fall for the "it’s so small it doesn’t matter" trap. Minimized video requires maximized quality. The encoding process magnifies shortcuts on quality.

Preprocessing Audio
Before encoding, preprocess audio and video tracks in order to maximize the post-encoding video quality. Preprocessing audio and video can be done within the timeline of an editor using available plug-ins. Alternately, preprocess audio separately from video using an audio mastering application. Then recombine the audio and video to build your master clip. If you process outside of a nonlinear editor, import the audio to the timeline and edit to picture, replacing original nonprocessed audio.
,br>Perform low-pass and high-pass filtering on your audio. This will reduce frequencies not reproducible in handsets due to the limited frequency response of miniature speakers. It will also reduce frequencies that will not encode well. AMR, for example, was designed as a speech codec, thus it does not encode the low and high frequencies in music very well. It is important, therefore, to reduce the low and high frequencies prior to encoding. Finally, the low and high filtering will reduce frequencies that when encoded will interfere with the clarity of the voice.

You will want to control the dynamics on the audio as well use normalization, compression, and limiting techniques. When the audio is normalized, the peak volume is identified and all audio is raised proportionally, maintaining the original dynamic range.

Proper compression creates a consistent audio level with a narrowed dynamic range. It raises the low-level audio and lowers the high-level audio, while maximizing the amount of audio signal going to the codec. Low-bitrate audio codecs typically do not have enough resolution to cleanly encode audio at low signal levels. Higher signal levels keep the codec working in the range where it sounds the best, with smoother sound quality.