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Apparatus and method of in-service audio/video synchronization testing
| Details |
Inventors: Kuhn, Karl J.; Zetts, John Mark;
Assignee: International Business Machines Corp. (Armonk, NY)
Primary Examiner: Vincent; David R.
Assistant Examiner:
Attorney, Agent or Firm: Redmond, Jr., Esq.; Joseph C. Morgan & Finnegan, LLP, Tomlin, Esq.; Richard A.
An apparatus and method provide non-intrusive in-service testing of audio/video synchronization testing without using traditional audio marker tones. The network includes an A/V synchronous test signal generator which injects video and audio markers into the video and audio non-intrusively and routes the two signals into a switch where they are switched into a channel for encoding and transmission via the ATM network. At the distant end the signal is decoded and routed by a switch into the A/V test generator and measurement set where the markers are detected and the A/V skew calculated, after which the audio and video are routed to the subscriber. The A/V test set signal generator includes a Video Blanking Interval (VBI) test signal generator and a white noise generator, the former injecting a marker into the video signal and the later injecting an audio marker into the audio signal. The video marker is injected into the VBI and broadband, background audio noise to measure the delay between the audio and video components of a broadcast. The marking of the audio is accomplished by gradually injecting white noise into the audio channel until the noise level is 6 dB above the noise floor of the audio receiver. As a precursor A/V sync signal, a small spectrum of the white noise is notched or removed. This signature precludes inadvertent recognition of program audio noise as the audio marker. |
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DETAILED DESCRIPTION An object of the invention is an in-service apparatus and method of non-intrusively measuring audio/video synchronization of a television broadcast across an analog, digital, or compressed digital transmission channel.
Another object is to measure A/V sync without using traditional audio marker tones.
These objects and other objects, features and advantages are accomplished in a network providing high bandwidth, broadcast quality video and audio signals.
In one embodiment, the analog and video signals are digitized and compressed.
The compressed digitized A/V signal is transmitted via an ATM network to a distant end where the signal is converted back into analog or digital format and passed on to the subscriber.
The network includes an A/V synchronous test signal generator which injects video and audio markers into the video and audio non-intrusively and routes the two signals into a switch where they are switched into a channel for encoding and transmission via the ATM network.
At the distant end the signal is decoded and routed by a switch into the A/V test generator set where the markers are detected and the A/V skew calculated, after which the audio and video are routed to the subscriber.
The A/V test set signal generator includes a Video Blanking Interval (VBI) test signal generator and a white noise generator, the former injecting.
a marker into the video signal and the later injecting an audio marker into the audio signal.
The video marker is injected into the VBI and broadband, background audio noise to measure the delay between the audio and video components of a broadcast.
The video marker is a single line of white injected into VBI for a duration of video one frame or 33 milliseconds.
The marking of the audio is accomplished by gradually injecting white noise into the audio channel until the noise level is 6 dB above the noise floor of the audio receiver.
The white noise is effectively masked by the audio program.
When a period of quiet occurs in the audio program, the injected white noise is removed for a period of 1 frame which is detected by the measurement test set as the audio marker
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