before

ffmpeg -i test.wav

Input #0, wav, from 'test.wav':
  Duration: 00:00:16.31, bitrate: 256 kb/s
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s

ffmpeg -i examples_sample.wav

Input #0, wav, from 'examples_sample.wav':
  Duration: 00:00:03.42, bitrate: 1572 kb/s
  Stream #0:0: Audio: pcm_s24le ([1][0][0][0] / 0x0001), 65536 Hz, mono, s32 (24 bit), 1572 kb/s

参数简要说明

-i 设定输入流
-f 设定输出格式
-ar 设定采样率
-ac 设定声音的channel数
-acodec 设定声音解码器

相同的输出设置：
ffmpeg命令行：ffmpeg -i example.wav -acodec pcm_s16le -ar 16000 -ac 1 out.wav
ffmpeg-python代码：

import ffmpeg
input_file='./examples_sample.wav' # 'test.wav'
(
    ffmpeg
    .input(input_file)
    .output('./testout1.wav',**{'ar':'16000','ac':'1','acodec':'pcm_s16le'})
    .run()
)

after

test.wav似乎没什么变化..前后格式一致

Input #0, wav, from './test.wav':
  Duration: 00:00:16.31, bitrate: 256 kb/s
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, wav, to './testout.wav':
  Metadata:
    ISFT            : Lavf58.76.100
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s
    Metadata:
      encoder         : Lavc58.134.100 pcm_s16le
size=     510kB time=00:00:16.25 bitrate= 256.9kbits/s speed=1.07e+03x
video:0kB audio:510kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.014943%

examples_sample.wav
可以观察到采样率有变化了... 文件大小位107kb

Input #0, wav, from './examples_sample.wav':
  Duration: 00:00:03.42, bitrate: 1572 kb/s
  Stream #0:0: Audio: pcm_s24le ([1][0][0][0] / 0x0001), 65536 Hz, mono, s32 (24 bit), 1572 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s24le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, wav, to './testout1.wav':
  Metadata:
    ISFT            : Lavf58.76.100
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s
    Metadata:
      encoder         : Lavc58.134.100 pcm_s16le
size=     107kB time=00:00:03.42 bitrate= 256.3kbits/s speed= 252x
video:0kB audio:107kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.071170%

改一下采样率为18000,可以发现文件大小为120kb，相同时间，更高的采样率，音频更大

stream = ffmpeg.input(input_file)
#stream = ffmpeg.hflip(stream)
stream = ffmpeg.output(stream, './testout2.wav',**{'ar':'18000','ac':'1','acodec':'pcm_s16le'})
ffmpeg.run(stream)

run

Input #0, wav, from './examples_sample.wav':
  Duration: 00:00:03.42, bitrate: 1572 kb/s
  Stream #0:0: Audio: pcm_s24le ([1][0][0][0] / 0x0001), 65536 Hz, mono, s32 (24 bit), 1572 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s24le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, wav, to './testout2.wav':
  Metadata:
    ISFT            : Lavf58.76.100
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 18000 Hz, mono, s16, 288 kb/s
    Metadata:
      encoder         : Lavc58.134.100 pcm_s16le
size=     120kB time=00:00:03.42 bitrate= 288.3kbits/s speed= 258x
video:0kB audio:120kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.063262%

上面的内容，主要还是一些知识点整理和个人的一些思考，权当参考，如有错误或者更好的建议，可以在评论区指正，不胜感激！