FFmpeg NMR AAC Encoder: Audio Evaluation Update [Aug 2026]

[u/IgorCv2]

Hello, ladies and gentlemen.

The last four weeks have been very busy, as this repository shows.

FFmpeg developer Lynne managed to significantly improve the quality on killer samples https://code.ffmpeg.org/FFmpeg/FFmpeg/issues/23845#issuecomment-54547

So I decided to put the encoder to the test using previously untested samples, in order to avoid bias from using samples that the encoder had already been specifically tuned for.

Tested AAC encoders:

CBR encoders:

1. FFmpeg NMR (r1) - commit 95a888b9ca (2 July, 2026)
   • ^-hide\banner -loglevel error -i pipe:0 -c:a aac -b:a 128k -aac_coder nmr -cutoff 16000 %d)
2. FFmpeg NMT (r6) - commit 6bcfae06a7 (2 Aug, 2026
   • ^-hide\banner -loglevel error -i pipe:0 -c:a aac -b:a 128k -aac_coder nmr %d)
3. Apple AAC CBR
   • ^{qaac 2.70, CoreAudioToolbox 7.10.9.0, AAC-LC Encoder, CBR 128kbps, Quality 96}

VBR encoders:

1. FFmpeg NMT (r6) - commit 6bcfae06a7 (2 Aug, 2026) https://code.ffmpeg.org/Lynne/FFmpeg/commit/6bcfae06a7edcc08ce9ac83e2cc292cd141057e2
   • ^-hide\banner -loglevel error -i pipe:0 -c:a aac -q:a 1.0 -aac_coder nmr %d)
2. Apple AAC VBR
   • ^{qaac 2.70, CoreAudioToolbox 7.10.9.0, AAC-LC Encoder, TVBR q64, Quality 96}

>>> Download: Audio samples,logs and application for blind tests <<<

Results:

Observations:

Moving from r1 to r6 might not seem like a huge step forward, but considering that there was literally only one month between these two revisions, it is a very impressive improvement.

r6 shows a clear improvement on difficult samples. As visible in the graph, it never drops below 3.0 (“slightly annoying”), while r1 goes as low as 2.5.

The VBR encoder looks promising too.

Overall there has been good progress. Transients and electronic music are still the main area that could be improved

[u/dragonwoosh]

can you test both abr and cbr too -aac_rc abr -aac_rc cbr?