FFMPEG:webm 到 mp4 质量损失

Question

尝试使用 ffmpeg(Mac 上为 3.4.2)将 .webm 视频(两种彩色动画)转换为 .mp4 视频时，结果有些模糊。我确实研究了这个主题并尝试了不同的方法来解决这个问题。这是最有希望的命令:

ffmpeg -i vidoe.webm -qscale 1 video.mp4

但是，质量变化仍然是巨大的，请参见下面的差异。

网站



mp4



两个视频的分辨率相同，但转换后大小从 24,3MB (.webm) 下降到 1,5MB (.mp4)。

更新

这是转换的日志。

ffmpeg version 3.4.2 Copyright (c) 2000-2018 the FFmpeg developers
  built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/3.4.2 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --disable-jack --enable-gpl --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
Input #0, matroska,webm, from 'video.webm':
  Metadata:
    encoder         : whammy
  Duration: 00:00:05.02, start: 0.000000, bitrate: 38755 kb/s
    Stream #0:0: Video: vp8, yuv420p(progressive), 1920x1080, SAR 1:1 DAR 16:9, 60 fps, 60 tbr, 1k tbn, 1k tbc (default)
Please use -q:a or -q:v, -qscale is ambiguous
Stream mapping:
  Stream #0:0 -> #0:0 (vp8 (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x7f8625800c00] -qscale is ignored, -crf is recommended.
[libx264 @ 0x7f8625800c00] using SAR=1/1
[libx264 @ 0x7f8625800c00] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x7f8625800c00] profile High, level 4.2
[libx264 @ 0x7f8625800c00] 264 - core 152 r2854 e9a5903 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'video.mp4':
  Metadata:
    encoder         : Lavf57.83.100
    Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], q=-1--1, 60 fps, 15360 tbn, 60 tbc (default)
    Metadata:
      encoder         : Lavc57.107.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
frame=  301 fps= 45 q=-1.0 Lsize=    1417kB time=00:00:04.96 bitrate=2336.4kbits/s speed=0.735x    
video:1412kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.309675%
[libx264 @ 0x7f8625800c00] frame I:2     Avg QP:13.08  size:  8842
[libx264 @ 0x7f8625800c00] frame P:75    Avg QP:24.29  size:  6785
[libx264 @ 0x7f8625800c00] frame B:224   Avg QP:26.38  size:  4102
[libx264 @ 0x7f8625800c00] consecutive B-frames:  0.7%  0.0%  1.0% 98.3%
[libx264 @ 0x7f8625800c00] mb I  I16..4: 68.1% 28.7%  3.2%
[libx264 @ 0x7f8625800c00] mb P  I16..4:  0.1%  2.2%  0.4%  P16..4:  6.5%  4.0%  1.4%  0.0%  0.0%    skip:85.4%
[libx264 @ 0x7f8625800c00] mb B  I16..4:  0.0%  0.2%  0.0%  B16..8:  8.8%  3.0%  0.3%  direct: 0.3%  skip:87.3%  L0:52.1% L1:47.5% BI: 0.4%
[libx264 @ 0x7f8625800c00] 8x8 transform intra:57.7% inter:67.8%
[libx264 @ 0x7f8625800c00] coded y,uvDC,uvAC intra: 25.7% 8.7% 0.9% inter: 3.9% 0.4% 0.0%
[libx264 @ 0x7f8625800c00] i16 v,h,dc,p: 95%  2%  3%  0%
[libx264 @ 0x7f8625800c00] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 17%  5% 48%  5%  7%  6%  5%  4%  3%
[libx264 @ 0x7f8625800c00] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 20% 14% 31%  6%  7%  7%  6%  5%  4%
[libx264 @ 0x7f8625800c00] i8c dc,h,v,p: 88%  6%  6%  0%
[libx264 @ 0x7f8625800c00] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x7f8625800c00] ref P L0: 55.3%  5.5% 24.8% 14.5%
[libx264 @ 0x7f8625800c00] ref B L0: 75.6% 16.7%  7.7%
[libx264 @ 0x7f8625800c00] ref B L1: 93.9%  6.1%
[libx264 @ 0x7f8625800c00] kb/s:2304.86

关于如何克服这种质量损失的任何想法？

Answer 1

更改 -qscale 1 至 -crf 1 解决了质量问题。工作命令是:

ffmpeg -i video.webm -crf 1 -c:v libx264 video.mp4

如 H.264 Video Encoding Guide 中所述-crf 接受从 0(无损)到 51(最差质量)的值。