A WebM file containing a movie which has a main video track and one alternate angle track, plus audio for both English and Spanish, in addition to audio for an English commentary track can be conceptualized as shown in the diagram below. Also included are text tracks containing closed captions for the feature film, Spanish subtitles for the film, and English captions for the commentary.
However, unlike previous format changes, e.g., vinyl to Compact Disc or VHS videotape to DVD, there is no immediate indication that production of the standard DVD will gradually wind down, as they still dominate, with around 75% of video sales and approximately one billion DVD player sales worldwide as of April 2011. In fact, experts claim that the DVD will remain the dominant medium for at least another five years as Blu-ray technology is still in its introductory phase, write and read speeds being poor and necessary hardware being expensive and not readily available.
The most common modulation technique is pulse-width modulation (PWM). Conceptually, PWM compares the input audio signal to a triangular or ramping waveform that runs at a fixed carrier frequency. This creates a stream of pulses at the carrier frequency. Within each period of the carrier, the duty ratio of the PWM pulse is proportional to the amplitude of the audio signal. In the example of Figure 7, the audio input and triangular wave are both centered around 0 V, so that for 0 input, the duty ratio of the output pulses is 50%. For large positive input, it is near 100%, and it is near 0% for large negative input. If the audio amplitude exceeds that of the triangle wave, full modulation occurs, where the pulse train stops switching, and the duty ratio within individual periods is either 0% or 100%. 2b1af7f3a8