I think your ffmpeg is too old to support lavfi. Find out by doing ffmpeg -formats. lavfi should be part of the list? You can try
ffmpeg -formats | grep lavfi
The following works fine otherwise.
ffmpeg -f lavfi -i amovie=sample1.aac,volumedetect
[aac @ 0x1e26a20] Estimating duration from bitrate, this may be inaccurate
[lavfi @ 0x1e25a60] Estimating duration from bitrate, this may be inaccurate
Input #0, lavfi, from 'amovie=sample1.aac,volumedetect':
Duration: N/A, start: 0.023220, bitrate: 1411 kb/s
Stream #0:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s
At least one output file must be specified
n_samples: 2048
[Parsed_volumedetect_1 @ 0x1e27280] mean_volume: -61.9 dB
[Parsed_volumedetect_1 @ 0x1e27280] max_volume: -49.0 dB
[Parsed_volumedetect_1 @ 0x1e27280] histogram_49db: 14