Does an audio watermark survive cropping?
Aureal does not need the file to start at a frame boundary. The detector searches for a key-derived chirp preamble and folds partial frames, so a clip cut from the middle can still decode. On the named 12 s fixture, 1.8 s excerpts recovered at 49 of 93 start offsets, and anything shorter than one frame (about 1 s at 44.1 kHz) never decoded.
How Aureal handles it
The payload repeats in frames of about one second. Instead of assuming the first sample is a frame start, detection cross-correlates the key-derived chirp preamble to find the sub-sample offset, then folds the available repetitions. For clips between roughly 1 s and 2 s, circular modulo folding lets fragments on both sides of a cut contribute to the same 48-symbol codeword. The mechanics explain why a mid-track cut is not automatically fatal, but they do not make short clips reliable: the offset sweep in the fixture still fails about half the time at 1.8 s, and a second encode on top reduces the margin further.
Common failure mode
“Cutting the first five seconds removes the watermark, because the file no longer starts at frame zero.”
Why it fails: The detector does not require a frame-aligned start. It searches for the preamble and recovers the frame phase from the audio itself. A five-second clip usually contains several frames, so the start offset is not the problem; total duration, codec damage and the signal-to-noise ratio in the carrier band are.
Verified example
Test the crop you actually plan to distribute, at more than one offset:
ffmpeg -ss 3.0 -t 1.8 -i marked.wav -c copy clip-a.wav
node aureal-watermark.cjs detect clip-a.wav --id 883921
ffmpeg -ss 7.4 -t 1.8 -i marked.wav -c copy clip-b.wav
node aureal-watermark.cjs detect clip-b.wav --id 883921
Record duration, offset and result; one passing offset is not a guarantee for the clip.Example only. Validate against your own audio, codec and processing chain.
Scope and limits
- Anything shorter than one frame (~1 s at 44.1 kHz) is never recovered.
- At 1.8 s, about half of the start offsets recovered on the named 12 s fixture (49/93).
- Result depends on source audio, codec and the offset of the cut.
- The reported carrier band can be wrong after filtering.
Frequently asked questions
How short can a clip be and still decode?
A complete frame is the floor: about 1 s at 44.1 kHz. Even around 1.8 s, recovery was partial and depended on the start offset in the local fixture. Test the exact clip rather than assuming a duration is safe.
Does trimming the intro remove the watermark?
Not by itself. The detector finds the frame phase from the preamble, so a mid-track cut can decode. If the remaining clip is too short or has been re-encoded, recovery can still fail.
Related topics
Test the actual delivery chain. A fixture result is a starting point, not a guarantee for your material.
Open the Studio →