Using audio filters throws Assertion best_input >= 0 failed

[Jozef Chutka]

Using the following order of audio filters:

ffmpeg -f lavfi -i anoisesrc=d=1 -af "aresample=22050,asplit[a][b];[a]anullsink;[b]atrim=end_sample=1" -f null -

throws:

Assertion best_input >= 0 failed at fftools/ffmpeg_filter.c:2118

Using verbose log level, this is full log:

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
Successfully parsed a group of options.
Parsing a group of options: input url anoisesrc=d=5.
Applying option f (force container format (auto-detected otherwise)) with argument lavfi.
Successfully parsed a group of options.
Opening an input file: anoisesrc=d=5.
[AVFilterGraph @ 0x138704cd0] Setting 'd' to value '5'
detected 8 logical cores
[AVFilterGraph @ 0x138704cd0] query_formats: 2 queried, 2 merged, 1 already done, 0 delayed
[lavfi @ 0x138704810] All info found
[lavfi @ 0x138704810] stream 0: start_time: 0 duration: NOPTS
[lavfi @ 0x138704810] format: start_time: 0 duration: NOPTS (estimate from bit rate) bitrate=3072 kb/s
Input #0, lavfi, from 'anoisesrc=d=5':
  Duration: N/A, start: 0.000000, bitrate: 3072 kb/s
  Stream #0:0, 1, 1/48000: Audio: pcm_f64le, 48000 Hz, mono, dbl, 3072 kb/s
Successfully opened the file.
Parsing a group of options: output url -.
Applying option af (alias for -filter:a (apply filters to audio streams)) with argument aresample=22050,asplit[a][b];[a]anullsink;[b]atrim=end_sample=1000.
Parsing stream specifier: a
Parsed media type: audio; remainder: 
Applying option f (force container format (auto-detected otherwise)) with argument null.
Successfully parsed a group of options.
Opening an output file: -.
[out#0/null @ 0x1387056c0] No explicit maps, mapping streams automatically...
[aost#0:0/pcm_s16le @ 0x138706df0] Created audio stream from input stream 0:0
[AVFilterGraph @ 0x138707c50] Setting 'sample_rate' to value '22050'
[AVFilterGraph @ 0x138707c50] Setting 'end_sample' to value '1000'
Successfully opened the file.
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_f64le (native) -> pcm_s16le (native))
[aost#0:0/pcm_s16le @ 0x138706df0] Starting thread...
[af#0:0 @ 0x138707830] Starting thread...
[aist#0:0/pcm_f64le @ 0x138705e50] [dec:pcm_f64le @ 0x138708960] Starting thread...
[in#0/lavfi @ 0x138704590] Starting thread...
Press [q] to stop, [?] for help
[AVFilterGraph @ 0x1399044e0] Setting 'sample_rate' to value '22050'
[AVFilterGraph @ 0x1399044e0] Setting 'end_sample' to value '1000'
[graph_-1_in_0:0 @ 0x139806a70] Setting 'time_base' to value '1/48000'
[graph_-1_in_0:0 @ 0x139806a70] Setting 'sample_rate' to value '48000'
[graph_-1_in_0:0 @ 0x139806a70] Setting 'sample_fmt' to value 'dbl'
[graph_-1_in_0:0 @ 0x139806a70] Setting 'channel_layout' to value 'mono'
[graph_-1_in_0:0 @ 0x139806a70] tb:1/48000 samplefmt:dbl samplerate:48000 chlayout:mono
[format_out_#0:0 @ 0x139807380] Setting 'sample_fmts' to value 's16'
[AVFilterGraph @ 0x1399044e0] query_formats: 7 queried, 12 merged, 6 already done, 0 delayed
[Parsed_aresample_0 @ 0x139806480] [SWR @ 0x130008000] Using dblp internally between filters
[Parsed_aresample_0 @ 0x139806480] ch:1 chl:mono fmt:dbl r:48000Hz -> ch:1 chl:mono fmt:s16 r:22050Hz
Output #0, null, to 'pipe:':
  Metadata:
    encoder         : Lavf61.7.100
  Stream #0:0, 0, 1/22050: Audio: pcm_s16le, 22050 Hz, mono, s16, 352 kb/s
      Metadata:
        encoder         : Lavc61.19.101 pcm_s16le
[out#0/null @ 0x1387056c0] Starting thread...
[out_#0:0 @ 0x139807220] EOF on sink link out_#0:0:default.
[in#0/lavfi @ 0x138704590] EOF while reading input
[in#0/lavfi @ 0x138704590] Terminating thread with return code 0 (success)
[aist#0:0/pcm_f64le @ 0x138705e50] [dec:pcm_f64le @ 0x138708960] Decoder thread received EOF packet
[aist#0:0/pcm_f64le @ 0x138705e50] [dec:pcm_f64le @ 0x138708960] Decoder returned EOF, finishing
[aist#0:0/pcm_f64le @ 0x138705e50] [dec:pcm_f64le @ 0x138708960] Terminating thread with return code 0 (success)
Assertion best_input >= 0 failed at fftools/ffmpeg_filter.c:2118
zsh: abort      ffmpeg -f lavfi -i anoisesrc=d=5 -af  -f null - -loglevel 1000

My original filter looks far more complex but the provided one is the minimalistic demo I could come up with for the related issue.

[Marton Balint]

Fixed in 44546751db824002f07cc0b8b2fc62587a5a34b5.