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Old 6th April 2011, 00:37   #1  |  Link
davroslyrad
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Sampling Frequency and Constant Duration

Greetings everyone,

I am developing systems using the ATSC-153 mobile broadcast. Part of the broadcast are the audio configuration tables which are to define parameters of the audio being broadcast.

Every broadcast I have worked with transmits the audio with 24Khz of sampling frequency, and the configurations tables indicate so. ATSC-153 defines the compression to be HEAAC-v2. So, for every AAC AU that is received gets an ADTS header, and everything works fine.

However, there is an exception. I have one broadcast in particular in which the configuration tables indicate the sampling frequency of 48Khz. The audio is actually 24Khz, and if I hard code the 24Khz index, the audio will play fine.

Competitor systems play the broadcast correctly. So, I can I can either think they are simply hard coding the index for 24Khz, or they figure out the sampling frequency by other means.

This particular broadcast also indicates a constant duration that other streams do not. By definition, the constant duration is the clock ticks the AU is. This deals more with the timestamps than sampling frequency.

So, the question is, is there a way of deriving the sampling frequency of the AU given the constant duration to go by? My thought is no, however I thought I would ask the community what their thoughts are.

Many thanks,

davroslyrad.
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aac, audio streams, mpeg4, samplerate

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