#11398: AVFoundation audio recordings have audible ticks and are missing samples
-------------------------------------+-------------------------------------
Reporter: drobinson | Type: defect
Status: new | Priority: normal
Component: | Version: 7.1
undetermined |
Keywords: | Blocked By:
avfoundation audio dropouts |
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Summary of the bug:
I am using macOS 15.1 (Sequoia) on a 2021 Apple M1 Pro MacBook Pro 14-inch
laptop, running FFmpeg version 7.1 installed via Homebrew.
Audio captured using AVFoundation through any audio codec (AAC, MP3, PCM,
or -c:a copy) produces audible glitches in the form of missing samples.
This issue occurs regardless of the sound device selected (built-in audio,
USB audio, etc.).
Originally, I ran into this issue while attempting to capture both video
and audio and encode them using libx264 and AAC. However, I found that the
issue persists even in the most basic use case—just recording audio
without video encoding.
Steps to Reproduce:
1. Record a known waveform with the following command:
{{{
ffmpeg -f avfoundation -i ":0" -c:a copy output.wav
}}}
2. Listen to output.wav. I notice frequent random audible ticks.
3. Inspect the waveform of output.wav in an audio editing tool (e.g.,
Reaper). I observed that the waveform exhibits discontinuities, where a
sequence of input samples, such as (1, 2, 3, 4, 5, 6, 7, 8, 9), results in
an output sequence like (1, 2, 3, 8, 9). In this example, samples 4, 5, 6,
and 7 are missing, and sample 8 immediately follows sample 3. These
missing samples occur randomly, typically every 3000-10000 samples, with
no discernible pattern.
Here is an example of a ramp waveform I used with the glitch circled in
red:
[[Image(https://i.ibb.co/rysLqqW/glitch.png)]]
And up close:
[[Image(https://i.ibb.co/hmKp3hT/glitch-close.png)]]
Expected Behavior:
The output audio should accurately represent the input without any missing
or skipped samples.
Actual Behavior:
There are consistent audio dropouts, where specific sections of audio are
completely missing, resulting in a glitchy sound. This happens with every
audio codec tested (AAC, MP3, PCM) and with different sound devices
(built-in, USB, etc.).
Details:
{{{
% ffmpeg -f avfoundation -i ":0" -c:a copy output.wav
ffmpeg version 7.1 Copyright (c) 2000-2024 the FFmpeg developers
built with Apple clang version 16.0.0 (clang-1600.0.26.4)
configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/7.1_4 --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. 19.100 / 61. 19.100
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
}}}
{{{
Input #0, avfoundation, from ':0':
Duration: N/A, start: 10114.532792, bitrate: 3072 kb/s
Stream #0:0: Audio: pcm_f32le, 48000 Hz, stereo, flt, 3072 kb/s
File 'output.wav' already exists. Overwrite? [y/N] y
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Output #0, wav, to 'output.wav':
Metadata:
ISFT : Lavf61.7.100
Stream #0:0: Audio: pcm_f32le ([3][0][0][0] / 0x0003), 48000 Hz, stereo,
flt, 3072 kb/s
Press [q] to stop, [?] for help
size= 1792KiB time=00:00:07.71 bitrate=1903.5kbits/s speed=1.28x
}}}
--
Ticket URL: <https://trac.ffmpeg.org/ticket/11398>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker
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