AAC 高质量编码 (ffmpeg)

AAC 音频编码分为 LC、HE-AAC、HEv2-AAC、LD、ELD；

HE-AAC 音频编码：

执行命令如下：

ffmpeg -i input.wav -c:a libfdk_aac -profile:a aac_he -b:a 96k output.m4a

执行命令后，编码输出output.m4a

Input #0, wav, from 'input.wav':
  Metadata:
    artist          : Blender Foundation 2008, Janus Bager Kristensen 2013
    comment         : Creative Commons Attribution 3.0 - http://bbb3d.renderfarming.net
    genre           : Animation
    title           : Big Buck Bunny, Sunflower version
    encoder         : Lavf57.83.100
  Duration: 00:10:34.14, bitrate: 4608 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 5.1(side), s16, 4608 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> aac (libfdk_aac))
Press [q] to stop, [?] for help
Output #0, ipod, to 'output.m4a':
  Metadata:
    artist          : Blender Foundation 2008, Janus Bager Kristensen 2013
    comment         : Creative Commons Attribution 3.0 - http://bbb3d.renderfarming.net
    genre           : Animation
    title           : Big Buck Bunny, Sunflower version
    encoder         : Lavf57.83.100
    Stream #0:0: Audio: aac (libfdk_aac) (HE-AAC) (mp4a / 0x6134706D), 48000 Hz, 5.1, s16, 96 kb/s
    Metadata:
      encoder         : Lavc57.107.100 libfdk_aac
size=    7493kB time=00:10:34.17 bitrate=  96.8kbits/s speed=31.1x    
video:0kB audio:7434kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.796552%

通过上面的转码信息，可以看出，音频编码为HE-AAC，可见编码参数已通过 -profile:a aac_he 已经设置生效；

AAC-ELD 音频编码：

执行命令如下：

ffmpeg -i input.wav -c:a libfdk_aac -profile:a aac_eld -b:a 96k output.m4a

执行命令后，编码输出output.m4a

Output #0, ipod, to 'output.m4a':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.27.103
    Stream #0:0(und): Audio: aac (libfdk_aac) (ELD) (mp4a / 0x6134706D), 44100 Hz, stereo, s16, 96 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      encoder         : Lavc58.52.102 libfdk_aac
size=     179kB time=00:00:14.94 bitrate=  98.0kbits/s speed=  37x