AFreadData

Routine

int AFreadData (AFILE *AFp, long int offs, float Fbuff[], int Nreq)

Purpose

Read data from an audio file (return float values)

Description

This routine returns a specified number of samples from an audio file. The data in the file is converted to float format on output. The sample data in the file is considered to be preceded and followed by zero-valued samples. Thus if offs is negative or points to beyond the number of samples in the file, the appropriate number of zero-valued samples are returned. The file must have been opened using routine AFopenRead.

The following program fragment illustrates the use of this routine to read overlapping frames of data. For the simpler case of sequential access to the data without overlap, the variable Lmem should be set to zero.

  AFp = AFopenRead (...);
  ...
  Lmem =...
  Lframe =...
  Nadv = Lframe-Lmem;
  offs = -Lmem;
  while (1) {
    Nout = AFreadData (AFp, offs, Fbuff, Lframe);
    offs = offs+Nadv;
    if (Nout == 0)
      break;
    ...
  }

Parameters

<- int AFreadData: Number of data values transferred from the file. On reaching the end of the file, Nout may be less than Nreq, in which case the last Nout-Nreq elements are set to zero. This value can be used by the calling routine to determine when the data from the file has been exhausted.
-> AFILE *AFp: Audio file pointer for an audio file opened by AFopenRead
-> long int offs: Offset into the file in samples. If offs is positive, the first value returned is offs samples from the beginning of the data. The file data is considered to be preceded by zeros. Thus if offs is negative, the appropriate number of zeros will be returned. These zeros before the beginning of the data are counted as part of the count returned in Nout.
<- float Fbuff[]: Array of floats to receive the Nreq samples
-> int Nreq: Number of samples requested. Nreq may be zero.

Author / revision