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用ffmpeg在webm传输流中生成时间戳

  •  0
  • Vlad Feinstein  · 技术社区  · 4 年前

    我正在将我的Electron应用程序的屏幕截图记录到一个文件中,如下所示: Save captured video to file in Electron

    建议使用 ffmpeg

    ffmpeg -fflags +genpts -i in.webm out.webm
    

    out.webm 这个文件比这个文件小15倍 in.webm ! 我看不出质量有任何变化。缺点是,处理时间与视频的持续时间大致相同。

    1. 有什么方法可以加快这个“时间戳”过程吗?
    2. 我可以录制一个已经小15倍的视频吗?

    maxFrameRate: 30 打电话的时候 webkitGetUserMedia() .

    这是该文件的输出 ffmpeg 命令:

    vlad$ ffmpeg -fflags +genpts -i in.webm out.webm
    ffmpeg version 4.3.2 Copyright (c) 2000-2021 the FFmpeg developers
      built with Apple clang version 12.0.0 (clang-1200.0.32.29)
      configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --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-librtmp --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
      libavutil      56. 51.100 / 56. 51.100
      libavcodec     58. 91.100 / 58. 91.100
      libavformat    58. 45.100 / 58. 45.100
      libavdevice    58. 10.100 / 58. 10.100
      libavfilter     7. 85.100 /  7. 85.100
      libavresample   4.  0.  0 /  4.  0.  0
      libswscale      5.  7.100 /  5.  7.100
      libswresample   3.  7.100 /  3.  7.100
      libpostproc    55.  7.100 / 55.  7.100
    Input #0, matroska,webm, from 'in.webm':
      Metadata:
        encoder         : Chrome
      Duration: N/A, start: 0.000000, bitrate: N/A
        Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv), 2560x1416, SAR 1:1 DAR 320:177, 1k tbr, 1k tbn, 1k tbc (default)
        Metadata:
          alpha_mode      : 1
    Stream mapping:
      Stream #0:0 -> #0:0 (vp9 (native) -> vp9 (libvpx-vp9))
    Press [q] to stop, [?] for help
    [libvpx-vp9 @ 0x7f85f2012600] v1.9.0
    [libvpx-vp9 @ 0x7f85f2012600] Neither bitrate nor constrained quality specified, using default CRF of 32
    Output #0, webm, to 'out.webm':
      Metadata:
        encoder         : Lavf58.45.100
        Stream #0:0(eng): Video: vp9 (libvpx-vp9), yuv420p, 2560x1416 [SAR 1:1 DAR 320:177], q=-1--1, 1k fps, 1k tbn, 1k tbc (default)
        Metadata:
          alpha_mode      : 1
          encoder         : Lavc58.91.100 libvpx-vp9
        Side data:
          cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
    frame=  209 fps=5.8 q=0.0 Lsize=     881kB time=00:00:17.81 bitrate= 405.0kbits/s speed=0.494x    
    video:879kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.231567%
    

    ffprobe :

    vlad$ ffprobe in.webm
    ffprobe version 4.3.2 Copyright (c) 2007-2021 the FFmpeg developers
      built with Apple clang version 12.0.0 (clang-1200.0.32.29)
      configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --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-librtmp --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
      libavutil      56. 51.100 / 56. 51.100
      libavcodec     58. 91.100 / 58. 91.100
      libavformat    58. 45.100 / 58. 45.100
      libavdevice    58. 10.100 / 58. 10.100
      libavfilter     7. 85.100 /  7. 85.100
      libavresample   4.  0.  0 /  4.  0.  0
      libswscale      5.  7.100 /  5.  7.100
      libswresample   3.  7.100 /  3.  7.100
      libpostproc    55.  7.100 / 55.  7.100
    Input #0, matroska,webm, from 'in.webm':
      Metadata:
        encoder         : Chrome
      Duration: N/A, start: 0.000000, bitrate: N/A
        Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv), 2560x1416, SAR 1:1 DAR 320:177, 1k tbr, 1k tbn, 1k tbc (default)
        Metadata:
          alpha_mode      : 1
    

    vlad$ ffprobe out.webm
    ffprobe version 4.3.2 Copyright (c) 2007-2021 the FFmpeg developers
      built with Apple clang version 12.0.0 (clang-1200.0.32.29)
      configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --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-librtmp --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
      libavutil      56. 51.100 / 56. 51.100
      libavcodec     58. 91.100 / 58. 91.100
      libavformat    58. 45.100 / 58. 45.100
      libavdevice    58. 10.100 / 58. 10.100
      libavfilter     7. 85.100 /  7. 85.100
      libavresample   4.  0.  0 /  4.  0.  0
      libswscale      5.  7.100 /  5.  7.100
      libswresample   3.  7.100 /  3.  7.100
      libpostproc    55.  7.100 / 55.  7.100
    Input #0, matroska,webm, from 'out.webm':
      Metadata:
        ENCODER         : Lavf58.45.100
      Duration: 00:00:17.82, start: 0.000000, bitrate: 405 kb/s
        Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv), 2560x1416, SAR 1:1 DAR 320:177, 1k tbr, 1k tbn, 1k tbc (default)
        Metadata:
          ALPHA_MODE      : 1
          ENCODER         : Lavc58.91.100 libvpx-vp9
          DURATION        : 00:00:17.815000000
    
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  •  2
  •   Armen Michaeli    4 年前

    我相当肯定您的FFmpeg处理并不是您想象的那样——使用命令行,尤其是在缺少某些显式开关的情况下,FFmpeg 将自行对视频和音频进行转码

    如果您只想生成大多数玩家所需的索引,

    ffmpeg -i <input-file> -codec copy <output-file>
    

    正如您可以从上面的命令行推测的那样,仅仅运行FFmpeg而没有任何与“生成帧时间索引”相关的显式开关,会导致它无论如何构建索引。无论是否进行代码转换,它都会这样做。

    还有一些球员,比如[现在被抛弃的] MPC-HC ,它们至少能够寻找一些传输流。我知道事实上,它可以寻找你的那种网络媒体。我不知道它实际上是如何进行搜索的确切细节,但如果我猜的话,我会说它只是从媒体中的某个适当位置(或最开始)对匹配搜索时间的帧进行线性搜索。很像在数据库表中查找一行,该行没有索引来帮助搜索谓词。