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I am trying to do some audio sync things (see Wikipedia on acoustic fingerprints).

I know it is possible to place watermarks in an audio signal to analyse it later, but how would I do to get the current time of a video? Would it be something like placing a watermark each second? Wouldn't placing so much watermarks create the risk of having false positive?

Also, I have tried to read audio frequencies on my Android phone (with zero crossing) but it is not very precise. So on a less conceptual topic: Could anyone advice me on a good way to detect audio watermark for smartphones/tablets?

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The idea of acoustic fingerprints, as the Wikipedia article mentions, is not to place watermarks in an audio signal but rather to be able to identify audio samples by creating a watermark from the sample. To get the current time from a video you'd most probably count the played frames and divide it by how many frames are played per second. Furthermore I feel this question is off-topic here as it's not related to programming in any conceptual way I could think of. –  zxcdw Mar 14 '13 at 16:44
    
Well I didn't find any better place for it. But it seems Audible Magic (listed on the wikipedia page I think) has been able to use watermarks to identify the current position in an audio file. And that's the kind of things I'm trying to do. –  Malharhak Mar 14 '13 at 16:48
    
What the program most probably does is that it takes samples very X seconds from which it builds a fingerprint which it stores along with the current position in a database. Then, once the sample plays again the program can tell the current time into the audio sample. But this approach requires the program to have a database of watermarks - it simply can't figure out the position on it's own. –  zxcdw Mar 14 '13 at 16:57
    
That's what I think too. But they have a link25 ms precision[/link], which seems really short for a watermark so I'm wondering if this sounds possible or if there is a more clever way. –  Malharhak Mar 14 '13 at 17:06
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