FFMPEG output truncated when adding watermark - audio

Question

I'm using the following command to generate a watermarked 320Kbps MP3 preview of a wav file:
ffmpeg -i /path/input.wav -y -filter_complex "amovie=/path/wm_padded.wav:loop=0,asetpts=N/SR/TB,adelay=3000|3000[beep];[0][beep]amix=duration=shortest,volume=2" -b:a 320k /path/preview.mp3
(wm_padded.wav is the watermark file padded to 10 seconds and I'm using a Mac. The command was structured based on this post)
While this works as expected at times, it produces a short, garbled preview some other times. Any help in debugging this issue would be greatly appreciated. I've verified the input file and it seems to be fine and here's the FFMPEG command output:
$ ffmpeg -i /path/input.wav -y -filter_complex "amovie=/path/wm_padded.wav:loop=0,asetpts=N/SR/TB,adelay=3000|3000[beep];[0][beep]amix=duration=shortest,volume=2" -b:a 320k -vsync 2 /path/test-Preview.mp3
ffmpeg version 4.2.1 Copyright (c) 2000-2019 the FFmpeg developers
built with Apple clang version 11.0.0 (clang-1100.0.33.8)
configuration: --prefix=/usr/local/Cellar/ffmpeg/4.2.1_2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/adoptopenjdk-13.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/adoptopenjdk-13.jdk/Contents/Home/include/darwin -fno-stack-check' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
libavutil 56. 31.100 / 56. 31.100
libavcodec 58. 54.100 / 58. 54.100
libavformat 58. 29.100 / 58. 29.100
libavdevice 58. 8.100 / 58. 8.100
libavfilter 7. 57.100 / 7. 57.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 5.100 / 5. 5.100
libswresample 3. 5.100 / 3. 5.100
libpostproc 55. 5.100 / 55. 5.100
[wav # 0x7ff2ba801a00] Discarding ID3 tags because more suitable tags were found.
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, wav, from '/path/input.wav':
Metadata:
comment : motion graphics, motion, textures
time_reference : 0
coding_history :
Duration: 00:00:01.75, bitrate: 1520 kb/s
Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
Stream #0:1: Video: mjpeg (Baseline), yuvj420p(pc, bt470bg/unknown/unknown), 288x288 [SAR 72:72 DAR 1:1], 90k tbr, 90k tbn, 90k tbc (attached pic)
Metadata:
comment : Cover (front)
[Parsed_amovie_0 # 0x7ff2b9d0c040] Channel layout is not set in output stream 0, guessed channel layout is 'stereo'
Stream mapping:
Stream #0:0 (pcm_s16le) -> amix:input0 (graph 0)
volume (graph 0) -> Stream #0:0 (libmp3lame)
Stream #0:1 -> #0:1 (mjpeg (native) -> png (native))
Press [q] to stop, [?] for help
[swscaler # 0x108d00000] deprecated pixel format used, make sure you did set range correctly
[Parsed_amovie_0 # 0x7ff2b9e09840] Channel layout is not set in output stream 0, guessed channel layout is 'stereo'
Output #0, mp3, to '/path/preview.mp3':
Metadata:
comment : motion graphics, motion, textures
time_reference : 0
coding_history :
TSSE : Lavf58.29.100
Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, stereo, fltp, 320 kb/s
Metadata:
encoder : Lavc58.54.100 libmp3lame
Stream #0:1: Video: png, rgb24(progressive), 288x288 [SAR 1:1 DAR 1:1], q=2-31, 200 kb/s, 90k fps, 90k tbn, 90k tbc (attached pic)
Metadata:
comment : Cover (front)
encoder : Lavc58.54.100 png
frame= 1 fps=0.0 q=-0.0 Lsize= 206kB time=00:00:00.10 bitrate=15994.8kbits/s speed=3.62x
video:200kB audio:5kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.598223%
Thanks in advance!

Answer 1

Upgrading to FFMPEG 2.8 solved the problem. On Mac, use:
brew install ffmpeg#2.8