mp3sr

Returns the sample rate encoded in an MP3 file, in Hz.

Use mp3sr to inspect a file before playback or compare its sample rate with the orchestra's rate. It reads file information at initialization and produces no audio.

Syntax

ModernClassic

ifilerate = mp3sr(Sfilename)
ifilerate = mp3sr(ifilcod)

ifilerate mp3sr Sfilename
ifilerate mp3sr ifilcod

Initialization

Sfilename is the filename or path of the MP3 file. Csound searches the current directory and the directories in SFDIR and SSDIR.

ifilcod is a numeric file code. It can select a filename assigned with strset, or be a score p-field containing a quoted filename. Without a matching string assignment, a numeric code selects a name such as soundin.1. Use integer codes for this form. A filename argument is required and has no default.

ifilerate is the sample rate from the stream header, in samples per second for each channel. For example, a 44.1 kHz file returns 44100. Stereo does not double this value. The compressed bit rate in bits per second is a separate property.

The result is an i-rate value read during initialization. It describes the file's encoded sample rate, independently of Csound's sr setting or any sample-rate conversion used during playback. Calling mp3sr neither changes sr nor resamples the file.

Availability and errors

mp3sr uses Csound's bundled MPEG decoder. It does not require the separate mp3out plugin or libsndfile's MP3 support. A build must include Csound's MP3 opcodes to provide it. For files in other audio formats, use filesr.

A missing file or a stream the decoder cannot read causes an initialization error. The opcode does not return 0 to indicate failure. An open-file error may name mp3in, which shares the file-reading code.

Examples

The example reads beats.mp3 and prints its sample rate beside Csound's sr value of 48000 Hz. It reports whether the two rates match. No audio plays.

Run it with beats.mp3 in the current directory or on Csound's sound-file search path. Change SFile to inspect another MP3 file.

It uses mp3sr.csd.

<CsoundSynthesizer>
<CsOptions>
-n -d
</CsOptions>
<CsInstruments>
sr = 48000
ksmps = 32
nchnls = 1
0dbfs = 1

instr ReportSampleRate
  SFile = "beats.mp3"
  iFileRate = mp3sr(SFile)
  prints "%s has a sample rate of %.0f Hz\n", SFile, iFileRate
  prints "Csound runs at %.0f Hz\n", sr
  if iFileRate == sr then
    prints "The sample rates match\n"
  else
    prints "The file and orchestra use different sample rates\n"
  endif
endin
</CsInstruments>
<CsScore>
i "ReportSampleRate" 0 0.01
e
</CsScore>
</CsoundSynthesizer>

See also

filesr, mp3len, strset, Sound File Queries

Credits

Author Victor Lazzarini, 2014.