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Rens's questions

Martin Hope
Rens
Asked: 2024-11-17 01:00:34 +0800 CST
  • 5

我正在尝试将音频文件中的语音片段分成几部分并将它们合并在一起。源音频是 16Khz 和 16 位的单轨 PCM Wav 文件。

使用-ss -i input.wav -t output.wav制作的切片与使用-ss -i input.wav -t -acodec copy output.wav制作的切片的持续时间不同

确切地说：

  • -ss 20.125 -i input.wav -t 10.125 output-reencode.wav 生成一个持续时间为 10s:125ms 的切片
  • -ss 20.125 -i input.wav -t 10.125 -acodec copy output-copy.wav 生成一个持续时间为 10s:176ms 的切片

为什么会有51ms的差异呢？

是否可以肯定地说，由于不涉及 PCM 压缩，重新编码版本不会更慢？

C:\Users\someuser>ffmpeg.exe -ss 20.125 -i "C:\input.wav" -t 10.125 "C:\output-reencode.wav"
ffmpeg version 7.0-essentials_build-www.gyan.dev Copyright (c) 2000-2024 the FFmpeg developers
  built with gcc 13.2.0 (Rev5, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-zlib --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-dxva2 --enable-d3d11va --enable-d3d12va --enable-ffnvcodec --enable-libvpl --enable-nvdec --enable-nvenc --enable-vaapi --enable-libgme --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libtheora --enable-libvo-amrwbenc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-librubberband
  libavutil      59.  8.100 / 59.  8.100
  libavcodec     61.  3.100 / 61.  3.100
  libavformat    61.  1.100 / 61.  1.100
  libavdevice    61.  1.100 / 61.  1.100
  libavfilter    10.  1.100 / 10.  1.100
  libswscale      8.  1.100 /  8.  1.100
  libswresample   5.  1.100 /  5.  1.100
  libpostproc    58.  1.100 / 58.  1.100
[aist#0:0/pcm_s16le @ 000001923d036b40] Guessed Channel Layout: mono
Input #0, wav, from 'C:\input.wav':
  Metadata:
    encoder         : Lavf61.1.100
    timecode        : 00:00:00:00
  Duration: 00:27:33.20, 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))
Output #0, wav, to 'C:\output-reencode.wav':
  Metadata:
    ISMP            : 00:00:00:00
    ISFT            : Lavf61.1.100
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s
      Metadata:
        encoder         : Lavc61.3.100 pcm_s16le
[out#0/wav @ 000001923d029e80] video:0KiB audio:316KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: 0.030247%
size=     317KiB time=00:00:10.12 bitrate= 256.1kbits/s speed=1.25e+03x

C:\Users\someuser>ffmpeg.exe -ss 20.125 -i "C:\input.wav" -acodec copy -t 10.125  "C:\output-copy.wav"
ffmpeg version 7.0-essentials_build-www.gyan.dev Copyright (c) 2000-2024 the FFmpeg developers
  built with gcc 13.2.0 (Rev5, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-zlib --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-dxva2 --enable-d3d11va --enable-d3d12va --enable-ffnvcodec --enable-libvpl --enable-nvdec --enable-nvenc --enable-vaapi --enable-libgme --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libtheora --enable-libvo-amrwbenc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-librubberband
  libavutil      59.  8.100 / 59.  8.100
  libavcodec     61.  3.100 / 61.  3.100
  libavformat    61.  1.100 / 61.  1.100
  libavdevice    61.  1.100 / 61.  1.100
  libavfilter    10.  1.100 / 10.  1.100
  libswscale      8.  1.100 /  8.  1.100
  libswresample   5.  1.100 /  5.  1.100
  libpostproc    58.  1.100 / 58.  1.100
[aist#0:0/pcm_s16le @ 000001ad5f9c9b80] Guessed Channel Layout: mono
Input #0, wav, from 'C:\input.wav':
  Metadata:
    encoder         : Lavf61.1.100
    timecode        : 00:00:00:00
  Duration: 00:27:33.20, 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 (copy)
Output #0, wav, to 'C:\output-copy.wav':
  Metadata:
    ISMP            : 00:00:00:00
    ISFT            : Lavf61.1.100
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s
Press [q] to stop, [?] for help
[out#0/wav @ 000001ad5f9c9d40] video:0KiB audio:318KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: 0.030095%
size=     318KiB time=00:00:10.24 bitrate= 254.5kbits/s speed=2.76e+03x
ffmpeg