[FFmpeg-trac] #11398(undetermined:new): AVFoundation audio recordings have audible ticks and are missing samples

[FFmpeg]

#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>
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