今天发现一个有趣的问题，b站下载的视频和音频时常是不一样的。

以前没注意，最近下的3d舞蹈的视频，需要自己把音频合到一起，发现有点延迟？感觉不舒服，回去看原视频很好，有点怪，不知道是b站做了什么处理。

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  ~/Movies ❯ ffmpeg -i '银狼 - [A]ddiction.mp4' -i '银狼 - [A]ddiction.m4a' -c:v copy -c:a aac -strict experimental '银狼 - [A]ddiction-with-audio.mp4'     14:38:02
ffmpeg version 6.0 Copyright (c) 2000-2023 the FFmpeg developers
  built with Apple clang version 14.0.3 (clang-1403.0.22.14.1)
  configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/6.0_1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d --enable-libjxl --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-audiotoolbox --enable-neon
  libavutil      58.  2.100 / 58.  2.100
  libavcodec     60.  3.100 / 60.  3.100
  libavformat    60.  3.100 / 60.  3.100
  libavdevice    60.  1.100 / 60.  1.100
  libavfilter     9.  3.100 /  9.  3.100
  libswscale      7.  1.100 /  7.  1.100
  libswresample   4. 10.100 /  4. 10.100
  libpostproc    57.  1.100 / 57.  1.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '银狼 - [A]ddiction.mp4':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: avc1iso5dsmsmsixdash
    encoder         : Lavf58.29.100
    description     : Packed by Bilibili XCoder v2.0.2
  Duration: 00:03:20.02, start: 0.000000, bitrate: 17498 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 3840x2160, 300 kb/s, 60 fps, 60 tbr, 16k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '银狼 - [A]ddiction.m4a':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: avc1iso5dsmsmsixdash
    encoder         : Lavf58.29.100
    description     : Packed by Bilibili XCoder v2.0.2
  Duration: 00:03:20.11, start: 0.000000, bitrate: 214 kb/s
  Stream #1:0[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 3 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #1:0 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
Output #0, mp4, to '银狼 - [A]ddiction-with-audio.mp4':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: avc1iso5dsmsmsixdash
    description     : Packed by Bilibili XCoder v2.0.2
    encoder         : Lavf60.3.100
  Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 3840x2160, q=2-31, 300 kb/s, 60 fps, 60 tbr, 16k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc60.3.100 aac
frame=12001 fps=3974 q=-1.0 Lsize=  430658kB time=00:03:20.08 bitrate=17632.2kbits/s speed=66.3x    
video:427106kB audio:3181kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.086380%
[aac @ 0x11d707a30] Qavg: 2234.092

  ~/Movies ❯ ls                                                                                                                                        7s  14:40:39
$RECYCLE.BIN
-弱点已植入?-.m4a
-弱点已植入?-.mp4
1 - 崩坏3「林海绮律」线上音乐会.m4a
1 - 崩坏3「林海绮律」线上音乐会.mp4
CacheClip
Captures
Infuse
Motion Templates.localized
Videos
[One Fansub] Sousou no Frieren - 13 [WebRip 1080p HEVC-10bits E-AC-3].mkv
bilibili
desktop.ini
hanser-background.mov
hanser除水印.jpg
hanser专辑曲《吵闹的雪》动画pv.m4a
hanser专辑曲《吵闹的雪》动画pv.mp4
iMovie Theater.theater
iMovie 剪辑资源库.imovielibrary
jjjunzhu水神芙宁娜动态壁纸标准屏.mp4
银狼 - Classic ~.m4a
银狼 - Classic ~.mp4
银狼 - [A]ddiction-with-audio.mp4
原神-HDR-低码率-险途勘探-1.mov
原神-HDR-高码率-险途勘探-1.mov
原神-HDR-高码率-险途勘探-2.mov
原神-HDR-低码率险途勘探-2.mov
重庆火锅&北京涮羊肉 谁更妙？！【祖娅纳惜×Hanser】绝涮双娇.m4a
重庆火锅&北京涮羊肉 谁更妙？！【祖娅纳惜×Hanser】绝涮双娇.mp4
《吵闹的雪》
我的猫狂奔了一整夜(原创曲).m4a

  ~/Movies ❯ ffmpeg -i '银狼 - Classic ~.mp4' -i '银狼 - Classic ~.m4a' -c:v copy -c:a aac -strict experimental 'w银狼 - Classic ~with-audio.mp4'           14:42:45
ffmpeg version 6.0 Copyright (c) 2000-2023 the FFmpeg developers
  built with Apple clang version 14.0.3 (clang-1403.0.22.14.1)
  configuration: --prefix=/opt/homebrew/Cellar/ffmpeg/6.0_1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d --enable-libjxl --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-audiotoolbox --enable-neon
  libavutil      58.  2.100 / 58.  2.100
  libavcodec     60.  3.100 / 60.  3.100
  libavformat    60.  3.100 / 60.  3.100
  libavdevice    60.  1.100 / 60.  1.100
  libavfilter     9.  3.100 /  9.  3.100
  libswscale      7.  1.100 /  7.  1.100
  libswresample   4. 10.100 /  4. 10.100
  libpostproc    57.  1.100 / 57.  1.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '银狼 - Classic ~.mp4':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: avc1iso5dsmsmsixdash
    encoder         : Lavf58.29.100
    description     : Packed by Bilibili XCoder v2.0.2
  Duration: 00:01:57.68, start: 0.000000, bitrate: 17466 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 3840x2160, 404 kb/s, 60 fps, 60 tbr, 16k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '银狼 - Classic ~.m4a':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: avc1iso5dsmsmsixdash
    encoder         : Lavf58.29.100
    description     : Packed by Bilibili XCoder v2.0.2
  Duration: 00:01:57.78, start: 0.000000, bitrate: 189 kb/s
  Stream #1:0[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 7 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #1:0 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
Output #0, mp4, to 'w银狼 - Classic ~with-audio.mp4':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: avc1iso5dsmsmsixdash
    description     : Packed by Bilibili XCoder v2.0.2
    encoder         : Lavf60.3.100
  Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 3840x2160, q=2-31, 404 kb/s, 60 fps, 60 tbr, 16k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc60.3.100 aac
frame= 7061 fps=4540 q=-1.0 Lsize=  252926kB time=00:01:57.76 bitrate=17594.9kbits/s speed=75.7x    
video:250826kB audio:1882kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.086433%
[aac @ 0x154707200] Qavg: 1057.115