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What is the definition error 2.4: PCR_accuracy_error?

問題:

What is the definition error 2.4: PCR_accuracy_error?

答案:

The formal definition of this error is given in the TR 101 290: Measurement guidelines for DVB systems document that is published by ETSI. A brief summary of this error is given below. For more information about this error or the test that generates it, please consult ETSI TR 101 290.

MPEG transport streams must periodically contain PCR (program clock register) values which are a snapshot of the encoders' program clock at the time that PCR value was generated. These values are then used on the decoder end to reconstruct the 27MHz system clock and ensure that the stream is kept in sync.

A PCR _accuracy_error occurs when a transmitted PCR value differs from what is expected by more than 500 nanoseconds. The expected PCR value is calculated using an extremely stable internal clock in the test device and previous PCR values. The calculated PCR is then compared to the transmitted PCR values to check for accuracy. It is important to note that most receivers do not contain very accurate clocks and therefore can be severely affected by this error.


此常見問答集適用於:

產品系列: MPEG 軟體 MPEG 分析儀

產品:

常見問答集 ID 64136

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