Generating and matching hashes of multimedia content
Hashes are short summaries or signatures of data files which can be used to identify the file. The disclosed method generates robust hashes for multimedia content, for example, audio clips. The audio clip is divided into successive (preferably overlapping) frames. For each frame, the frequency spectrum is divided into bands. A robust property of each band (e.g. energy) is computed and represented by a respective hash bit. An audio clip is thus represented by a concatenation of binary hash words, one for each frame. To identify a possibly compressed audio signal, a block of hash words derived therefrom is matched by a computer with a large database. Such matching strategies are also disclosed. In an advantageous embodiment, the extraction process also provides information as to which of the hash bits are the least reliable. Flipping these bits considerably improves the speed and performance of the matching process.
1. A method to identify multimedia content, the method comprising:
receiving an input block of hash words, the input block representing at least a part of an information signal;
interrogating a look-up table with a selected hash word from the input block to obtain a found hash word;
comparing, by a computer, the input block and a stored block of hash words in which the found hash word has the same position as the selected hash word;
selectively identifying the stored block of hash words as a matching reference signal based on the outcome of the comparing;
wherein the selected hash word comprises a plurality of reliable hash bits and unreliable hash bits; and
the interrogating comprises interrogating the look-up table with reliable bits of the selected hash word.
2. The method of claim 1 , further comprising selecting a further hash word in response to determining that the difference between the input block and the stored block is greater than a predetermined threshold.
3. The method of claim 2 , wherein the selecting of the further hash word comprises reversing an unreliable bit from the selected hash word.
4. The method of claim 3 , wherein the selecting of the further hash word comprises:
receiving information indicative of reliability of a bit of the selected hash word; and
using said the information to determine the unreliable bit.
5. The method of claim 1 , wherein the selectively identifying of the stored block of hash words as a matching reference signal comprises:
calculating a bit error rate between bits of the input block and corresponding bits of the stored block; and
identifying the stored block of hash words as the matching reference signal based on the calculated bit error rate.
6. The method of claim 1 , further comprising returning an identification associated with the stored block.
7. A method to identify subject content, the method comprising:
receiving a hash value associated with an information signal, the hash value comprising one or more reliable hash bits and one or more unreliable hash bits;
interrogating a look up table with the one or more reliable bits to determine one or more matching stored hash values;
for each of the one or more matching stored hash values, calculating, by a computer, a bit error rate, the bit error rate representing a relationship between the one or more bits of the hash value and the corresponding bits of a matching stored hash value from the one or more matching stored hash values;
selecting a matching stored hash value from the one or more matching stored hash values, for which the bit error rate is minimal; and
identifying the matching stored hash value, for which the bit error rate is minimal, as the matching stored hash value associated with the subject content.
8. The method of claim 7 , wherein the subject content is audio content.
9. The method of claim 7 , wherein the subject content is video content.