ffmpeg # -strict -2

The native FFmpeg AAC encoder. This is currently the second highest-quality AAC encoder available in FFmpeg and does not require an external library like the other AAC encoders described here. This is the default AAC encoder.

Note: -strict experimental (or -strict -2) was previously required for this encoder, but it is no longer experimental and these options are unnecessary since 5 December 2015.

-strict -2 之前是实验参数表示 aac音频编码

References:

https://blog.csdn.net/jeffasd/article/details/71194263