private void ShowFingerprints(SubFingerprintLookupEntry sfp1, SubFingerprintLookupEntry sfp2)
{
Fingerprint fp1 = store.GetFingerprint(sfp1);
Fingerprint fp2 = store.GetFingerprint(sfp2);
Fingerprint fpDifference = fp1.Difference(fp2);
fingerprintView1.Fingerprint = fp1;
fingerprintView2.Fingerprint = fp2;
fingerprintView3.Fingerprint = fpDifference;
berLabel.Content = Fingerprint.CalculateBER(fp1, fp2);
}
public List <Match> FindMatchesFromExternalSubFingerprints(AudioTrack audioTrack, List <SubFingerprintHash> hashes)
{
if (hashes.Count < this.fingerprintSize)
{
throw new ArgumentException(String.Format(
"Hash list is too short, cannot build fingerprints (given {0}, required at least {1})",
hashes.Count, this.fingerprintSize));
}
var matches = new List <Match>();
int collisionCount = 0;
for (int i = 0; i < hashes.Count; i++)
{
List <SubFingerprintLookupEntry> collisions = this.collisionMap.GetValues(hashes[i]);
foreach (var collision in collisions)
{
collisionCount++;
// The indices at which the fingerprints begin within the hash lists
int externalIndex = i;
int internalIndex = collision.Index;
// The hash lists
var externalHashes = hashes;
var internalHashes = store[collision.AudioTrack];
// The lengths of the hash lists (the number of subfingerprints/hashes)
int externalHashCount = externalHashes.Count;
int internalHashCount = internalHashes.Count;
// The overflow if directly taken at the indices
int externalOverflow = this.fingerprintSize - (externalHashCount - externalIndex);
int internalOverflow = this.fingerprintSize - (internalHashCount - internalIndex);
// The bigger of both overflows is the value by which we need to shift the sampling to the left
int leftShift = Math.Max(externalOverflow, internalOverflow);
// Check if we need to do a shift
// If the left shift is > 0, we need to shift the fingerprints to the left
// if the shift is <= 0, the fingerprints can be directly sampled from the hash lists
// (the negative value is their distance to the right border)
if (leftShift > 0)
{
// We need to shift the fingerprints to the left because one or both would otherwise overflow the right border
externalIndex -= leftShift;
internalIndex -= leftShift;
// Before we take the fingerprints, we need to check if that is even possible or if a fingerprint
// would then overflow the left border
if (externalIndex < 0 || internalIndex < 0)
{
// A fingerprint would now overflow the left border, so for this collision it is not possible
// to take fingerprints that we can compare
// Skip to the next collision
continue;
}
}
// TODO detect duplicate matching attempts and skip them to minimize matching cost
// A matching attempt can be described as the tuple (internalAudioTrack, externalIndex, internalIndex)
// Take the fingerprints that we want to compare
Fingerprint externalFingerprint = new Fingerprint(externalHashes, externalIndex, this.fingerprintSize);
// We don't use GetFingerprint here because that function shifts the fingerprint left for an unknown offset
// if taken at the right border
Fingerprint internalFingerprint = new Fingerprint(internalHashes, internalIndex, this.fingerprintSize);
// Calculate the bit error rate between both fingerprints
float bitErrorRate = Fingerprint.CalculateBER(externalFingerprint, internalFingerprint);
Console.WriteLine(String.Format("{0} <> {1} => {2}", externalIndex, internalIndex, bitErrorRate));
if (bitErrorRate < threshold)
{
matches.Add(new Match {
Similarity = 1 - bitErrorRate,
Track1 = collision.AudioTrack,
Track1Time = SubFingerprintIndexToTimeSpan(internalIndex),
Track2 = audioTrack,
Track2Time = SubFingerprintIndexToTimeSpan(externalIndex),
Source = matchSourceName,
});
}
}
}
Console.WriteLine(String.Format("{0} collisions, {1} matches", collisionCount, matches.Count));
return(matches);
}