examples/fpcalc.c invalid buffer length?

[Johan Ström]

Hi,

I'm playing around with your fpcalc example code, and I noticed something which I think is a bug: At fpcalc.c line 173 (https://bitbucket.org/acoustid/chromaprint/src/51c46effb3beac17345b7920ec6eda68077dc612/examples/fpcalc.c?at=master#cl-173) the number of bytes in the data buffer is calculated:

length = MIN(remaining, frame->nb_samples * codec_ctx->channels);

This however assumes that each sample is 1 byte. Since it always converts to AV_SAMPLE_FMT_S16, every sample is 2 bytes? The proper(?) code would instead be:

length = MIN(remaining, frame->nb_samples * codec_ctx->channels * av_get_bytes_per_sample(AV_SAMPLE_FMT_S16));

"remaining" would also need to be adjusted accordingly.

If I'm correct here, this means we feed only the first 50% of the samples in each frame into the fingerprinting algorithm.

Am I misunderstanding something, or is this a valid bug? Thanks

[Johan Ström]

Never mind, my bad. chromaprint_feed takes nr of 16bit samples... not bytes..

/**
 * Send audio data to the fingerprint calculator.
 *
 * Parameters:
 *  - ctx: Chromaprint context pointer
 *  - data: raw audio data, should point to an array of 16-bit signed
 *          integers in native byte-order
 *  - size: size of the data buffer (in samples)
 *
 * Returns:
 *  - 0 on error, 1 on success
 */
CHROMAPRINT_API int chromaprint_feed(ChromaprintContext *ctx, void *data, int size);

It was just me confusing myself when doing some debugging.

[Lukáš Lalinský]

Yeah, taking the number of 16 bit samples rather than bytes was an arbitrary decision. Let me know if the docs could be clearer.