转码为 webm 时的 Ffmpeg 性能问题

Question

我最近将 ffmpeg 从版本 2.0.2 更新到最新版本 2.7。我使用与旧版本相同的构建配置和相同的编解码器版本（libvpx 和 h264）安装它。当我尝试将 mp4 视频转码为 webm 时，我发现新版本的速度明显低于旧版本（3 倍）。我运行在两台相同的 8 核机器上（Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz）- OS: Ubuntu 14.04。下面是命令我运行:

/usr/local/bin/ffmpeg -i in.mp4 -f webm -vcodec libvpx -b:v 1000K out.webm

这些是两个版本的输出：

v 2.0.2

ffmpeg version 2.0.2 Copyright (c) 2000-2013 the FFmpeg developers
built on Jan  7 2015 13:51:25 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
configuration: --disable-ffplay --disable-ffserver --enable-libxvid --enable-gpl --enable-nonfree --enable-pthreads --enable-libmp3lame --enable-libx264 --enable-libfaac --enable-zlib --enable-avfilter --enable-libfreetype --enable-libfdk_aac --enable-libtheora --enable-libvorbis --enable-libvpx --enable-pic --enable-shared  
libavutil      52. 38.100 / 52. 38.100
libavcodec     55. 18.102 / 55. 18.102
libavformat    55. 12.100 / 55. 12.100
libavdevice    55.  3.100 / 55.  3.100
libavfilter     3. 79.101 /  3. 79.101
libswscale      2.  3.100 /  2.  3.100
libswresample   0. 17.102 /  0. 17.102
libpostproc    52.  3.100 / 52.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'in.mp4':
Metadata:
major_brand     : isom
minor_version   : 512
compatible_brands: isomiso2avc1mp41
encoder         : Lavf55.12.100
Duration: 00:00:10.19, start: 0.000000, bitrate: 1724 kb/s
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1480 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
Metadata:
  handler_name    : VideoHandler
Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 253 kb/s
Metadata:
  handler_name    : SoundHandler
[libvpx @ 0x22f3760] v1.3.0
Output #0, webm, to 'out.webm':
Metadata:
major_brand     : isom
minor_version   : 512
compatible_brands: isomiso2avc1mp41
encoder         : Lavf55.12.100
Stream #0:0(und): Video: vp8 (libvpx), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], q=-1--1, 1000 kb/s, 1k tbn, 29.97 tbc
Metadata:
  handler_name    : VideoHandler
Stream #0:1(und): Audio: vorbis (libvorbis), 44100 Hz, stereo, fltp
Metadata:
  handler_name    : SoundHandler
Stream mapping:
Stream #0:0 -> #0:0 (h264 -> libvpx)
Stream #0:1 -> #0:1 (aac -> libvorbis)
Press [q] to stop, [?] for help
frame=  302 fps= 23 q=0.0 Lsize=    1445kB time=00:00:10.18 bitrate=1161.9kbits/s    
video:1304kB audio:128kB subtitle:0 global headers:4kB muxing overhead 0.644833%

v 2.7

ffmpeg version 2.7 Copyright (c) 2000-2015 the FFmpeg developer built with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  configuration: --disable-ffplay --disable-ffserver --enable-libxvid --enable-gpl --enable-nonfree --enable-libmp3lame --enable-libx264 --enable-libfaac --enable-zlib --enable-libass --enable-pthreads --enable-avfilter --enable-libfreetype --enable-libfdk_aac --enable-libtheora --enable-libvorbis --enable-libvpx --enable-pic --enable-shared --enable-openssl
  libavutil      54. 27.100 / 54. 27.100
  libavcodec     56. 41.100 / 56. 41.100
  libavformat    56. 36.100 / 56. 36.100
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 16.101 /  5. 16.101
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.100 /  1.  2.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'in.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf56.36.100
  Duration: 00:00:10.19, start: 0.000000, bitrate: 1596 kb/s
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1480 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
[libvpx @ 0xfe4640] v1.3.0
Output #0, webm, to 'out.webm':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf56.36.100
    Stream #0:0(und): Video: vp8 (libvpx), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], q=-1--1, 1000 kb/s, 29.97 fps, 1k tbn, 29.97 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc56.41.100 libvpx
    Stream #0:1(und): Audio: vorbis (libvorbis), 44100 Hz, stereo, fltp (default)
    Metadata:
      handler_name    : SoundHandler
      encoder         : Lavc56.41.100 libvorbis
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> vp8 (libvpx))
  Stream #0:1 -> #0:1 (aac (native) -> vorbis (libvorbis))
Press [q] to stop, [?] for help
frame=  302 fps=8.3 q=0.0 Lsize=    1410kB time=00:00:10.18 bitrate=1133.4kbits/s    
video:1274kB audio:123kB subtitle:0kB other streams:0kB global headers:4kB muxing overhead: 0.909304%

我试过 ffmpeg 2.6.3，性能和 2.7 一样。另外看起来当我将 webm 转码为 mp4 2.7 比 webm 快 30%。

我试图查看是否有新版本的构建配置选项，但没有找到任何内容。

谁能提出新版本在转码为 webm 时速度性能较差的可能原因？

Answer 1

我有运行带有 -loglevel 99 的命令，我检查了日志。我发现 vpx 编解码器选项有所不同：

v2.0.2：

[libvpx @ 0x1e18780] vpx_codec_control
[libvpx @ 0x1e18780]   VP8E_SET_CPUUSED: 3

v2.7：

[libvpx @ 0x1e18780] vpx_codec_control
[libvpx @ 0x1e18780]   VP8E_SET_CPUUSED: 1

看来新版本的ffmpeg默认设置为1。要从 ffmpeg 手动设置此参数，我必须添加选项：“-speed”。此选项的说明在 http://www.webmproject.org/docs/webm-sdk/group__vp8__encoder.html . I found the reference of the speed option in ffmpeg only in the ffmpeg developers mailing list: http://ffmpeg.org/pipermail/ffmpeg-devel/2011-January/105630.html 中。使用命令：

/usr/local/bin/ffmpeg -i in.mp4 -f webm -vcodec libvpx -b:v 1000K -speed 3 out.webm

我在 ffmpeg 2.0.2 和 2.7 中获得了相同的性能。我尝试增加该值，并取得了显着的速度提升。从视觉评估来看，b:v 选项（比特率）似乎可以保证质量。

转码为 webm 时的 Ffmpeg 性能问题

Ffmpeg performance issue when transcoding to webm

video

ffmpeg

webm

libvpx