FFmpeg hangs when using apad filter along with shortest flag

[Krzysztof Paliga]

Summary of the bug: When using the apad filter along with -shortest flag, the ffmpeg process keeps running without ever finishing.

Test file URL: ​https://bn-stream-e2e.b-cdn.net/hdr.mov

How to reproduce:

% ffmpeg -loglevel verbose -fflags +genpts -i hdr.mov -shortest -c:v copy -c:a aac -af apad,aresample=async=1:first_pts=0 -y tmpPaddingFix.mp4
ffmpeg version 7.0.1 Copyright (c) 2000-2024 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.4.0-1ubuntu1~20.04.2)
  configuration: --prefix=/usr --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --disable-stripping --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-libdav1d --enable-libzimg --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-frei0r --enable-libx264 --enable-shared --enable-nonfree --enable-version3 --enable-gpl --arch=x86_64 --extra-libs='-lpthread -lm' --extra-cflags='-Os -march=sandybridge -mtune=znver2'
  libavutil      59.  8.100 / 59.  8.100
  libavcodec     61.  3.100 / 61.  3.100
  libavformat    61.  1.100 / 61.  1.100
  libavdevice    61.  1.100 / 61.  1.100
  libavfilter    10.  1.100 / 10.  1.100
  libswscale      8.  1.100 /  8.  1.100
  libswresample   5.  1.100 /  5.  1.100
  libpostproc    58.  1.100 / 58.  1.100

Verbose output:

[out#0/mp4 @ 0x5582bb8b2300] Starting thread...
[in#0/mov,mp4,m4a,3gp,3g2,mj2 @ 0x5582bb8ab680] EOF while reading input
[in#0/mov,mp4,m4a,3gp,3g2,mj2 @ 0x5582bb8ab680] Terminating thread with return code 0 (success)
[aist#0:1/aac @ 0x5582bb9258c0] [dec:aac @ 0x5582bb8b1540] Decoder thread received EOF packet
[aist#0:1/aac @ 0x5582bb9258c0] [dec:aac @ 0x5582bb8b1540] Decoder returned EOF, finishing
[aist#0:1/aac @ 0x5582bb9258c0] [dec:aac @ 0x5582bb8b1540] Terminating thread with return code 0 (success)
[out#0/mp4 @ 0x5582bb8b2300] Muxer returned EOF
[out#0/mp4 @ 0x5582bb8b2300] Terminating thread with return code 0 (success)

This workflow works perfectly on version 5.1.4 and 6.0.1. I looked at the changelog, but there are no mentions of apad changes, so I figured I file a bug report.