AFopenRead(3tsp)

Routine
AFILE *AFopenRead (const char Fname[], long int *Nsamp, long int *Nchan, float *Sfreq, FILE *fpinfo)

Purpose
Open an audio file for reading

Description
This routine opens an audio file for reading. The companion routine AFreadData reads data from the file. Routine AFclose should be used to close the file.

This routine reads the audio file header and optionally prints the header information. Several file header formats are supported. For files with no header or an unrecognized header, the file format can be declared by calling routine AFsetNHpar. A banner identifying the audio file and its parameters is printed.

AU audio file:
8-bit mu-law, 8-bit A-law, 8-bit integer, 16-bit integer, 24-bit integer, 32-bit integer, 32-bit IEEE floating-point, and 64-bit IEEE floating-point data formats are supported.
RIFF WAVE:
8-bit mu-law, 8-bit A-law, offset-binary 1-bit to 8-bit integer, 9-bit to 32-bit integer, 32-bit IEEE floating-point, and 64-bit IEEE floating-point data formats are supported.
AIFF or AIFF-C audio file:
8-bit mu-law, 8-bit A-law, 1-bit to 32-bit integer, 32-bit IEEE floating-point, and 64-bit IEEE floating-point data formats are supported.
NIST SPHERE audio file:
8-bit mu-law and 16-bit integer data formats are supported.
IRCAM soundfile:
8-bit mu-law, 8-bit A-law, 8-bit integer, 16-bit integer, 32-bit integer, and 32-bit floating-point data formats are supported.
ESPS sampled data feature file:
16-bit integer, 32-bit integer, 32-bit floating-point, and 64-bit floating-point data formats are supported.
SPPACK sampled data file:
8-bit mu-law, 8-bit A-law and 16-bit integer data formats are supported.
INRS-Telecommunications audio file:
16-bit integer format is supported.
Cadence SPW Signal file:
8-bit integer, 16-bit integer, 32-bit floating-point, 64-point floating-point, and text formats are supported.
Text audio file:
Data in character format (usually representing 16-bit integer values).
Headerless audio file:
The data format is specified by calling routine AFsetNHpar.

For the fixed point file data representations, read operations return data values as follows.
   format            returned values
  8-bit mu-law   - [ -32124, +32124 ]
  8-bit A-law    - [ -32256, +32256 ]
  8-bit integer  - [ -16384, -16383 ]
  16-bit integer - [ -32768, +32767 ]
  24-bit integer - [ -32768, +32768 )
  32-bit integer - [ -32768, +32768 )
Floating-point data in the input audio file are scaled by 32768 (except for ESPS sample data feature files). For file float data values between -1 and +1, the returned values will be in the range [ -32768, +32768 ].

File type determination:
The default behaviour is to determine the file type from the header of the input file. However this requires look-ahead and is not possible with files that are not random access (for instance a file stream from a pipe). For both random access and sequential access files, the file type can be specified explicitly with a call to routine AFsetFileType, obviating the need to determine the file type from the header.

Number of samples:
In some types of audio file types, the number of samples is specified in the file header. In others, the number of samples is known only if the file size can be determined, specifically if the file random access. For input from a stream which does not allow random access (for instance a file stream from a pipe), the file size cannot be determined for those files without that information in the file header.
                  no. samples
 file type         in header
 AU                  yes
 RIFF WAVE           yes
 AIFF or AIFF-C      yes
 NIST SPHERE         yes
 IRCAM               no
 ESPS                yes
 SPPACK              yes
 INRS-Telecom        no
 Comdisco SPW        no
 Text file           no
 Headerless          no
Notes:
- Some AU audio files and some ESPS audio files do not specify the number of samples.
- AIFF/AIFF-C files with a perverse header cannot be opened for non-random access.

On encountering an error, the default behaviour is to print an error message and halt execution.

Parameters
<- AFILE *AFopenRead
Audio file pointer for the audio file.. The file name "-" means standard input.
 -> const char Fname[]
Character string specifying the file name
<- long int *Nsamp
Total number of samples in the file (all channels)
<- long int *Nchan
Number of channels
<- float *Sfreq
Sampling frequency
 -> FILE *fpinfo
File pointer for printing audio file information. If fpinfo is not NULL, information about the audio file is printed on the stream selected by fpinfo.

Author / revision
P. Kabal Copyright (C) 1999 / Revision 1.77 1999/06/14

See Also
AFreadData, AFsetFileType, AFsetNHpar, AFclose, AFsp