numberOfChannels reported as 2 for a single channel, mono, audio file

[itsramiel]

Description

Hi,

I am trying to retrieve the channel count for an audio file. My file is mono, single channel. This can be checked with ffmpeg

ffmpeg -i assets/mono.wav                                            1m 33s 10:11:00 AM
ffmpeg version 7.1.1 Copyright (c) 2000-2025 the FFmpeg developers
  built with Apple clang version 17.0.0 (clang-1700.0.13.3)
  configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/7.1.1_3 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags='-Wl,-ld_classic' --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d --enable-libharfbuzz --enable-libjxl --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-audiotoolbox --enable-neon
  libavutil      59. 39.100 / 59. 39.100
  libavcodec     61. 19.101 / 61. 19.101
  libavformat    61.  7.100 / 61.  7.100
  libavdevice    61.  3.100 / 61.  3.100
  libavfilter    10.  4.100 / 10.  4.100
  libswscale      8.  3.100 /  8.  3.100
  libswresample   5.  3.100 /  5.  3.100
  libpostproc    58.  3.100 / 58.  3.100
[aist#0:0/pcm_s16le @ 0x1569042f0] Guessed Channel Layout: mono
Input #0, wav, from 'assets/mono.wav':
  Metadata:
    encoder         : Sony Sound Forge 7.0
    title           : Large fan
    IENG            : Sebastian Lindstr�m
    copyright       : Copy freely
    comment         : Large fanblades?
                    : No. A recording of an attempt to
                    : create the sound of an explosion using several clicks, modified with Accoustic Mirror using an audio sample of a preast reading the latin prayer 'Pater Noster', heavily flanged, reversed, flanged again, then crossfaded into a perfect loop?
                    : Yes.
                    : So... fanblades. Useful? You decide.
    ISBJ            : oh, for the love of... it's noise, ok!?
    date            : 2013-05-15
  Duration: 00:00:05.00, bitrate: 769 kb/s
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, mono, s16, 768 kb/s
At least one output file must be specified

However when I retrieve it using react-native-audio-api after creating an AudioBuffer, the reported channelCount is 2

Steps to reproduce

1. Clone repro
2. Run app
3. Observe how the logged number is 2
4. Retrieve channel count with ffmpeg
5. Observe how output mentions mono

Snack or a link to a repository

https://github.com/itsramiel/AudioApidChannelCount

React Native Audio API version

0.8.2

React Native version

0.81.4

Platforms

Android, iOS

JavaScript runtime

Hermes

Workflow

React Native

Architecture

Fabric (New Architecture)

Build type

Debug app & dev bundle

Device

Android emulator

Device model

No response

Acknowledgements

Yes

[mdydek]

Hi, the reason for that is because the final destination (phone speakers) is always expecting 2 channels at the end. That is way it was designed like that initially, but the refactor is coming. Will leave the issue if someone else would have similar questions.