问题
When trying to convert a .webm video (two colored animation) to a .mp4 video using ffmpeg (3.4.2 on mac) the result is somewhat blurry. I did research this topic and tried different approaches to solve this. Here is the most promising command:
ffmpeg -i vidoe.webm -qscale 1 video.mp4
However, the quality change is still tremendous, see the difference below.
webm
mp4
The resolution of the two videos is the same, however the size dropped from 24,3MB (.webm) to 1,5MB (.mp4) after conversion.
Update
Here is the log of the conversion.
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
Any idea on how to overcome this quality loss?
回答1:
Changing -qscale 1 to -crf 1 resolves the quality issue. The working command is:
ffmpeg -i video.webm -crf 1 -c:v libx264 video.mp4
As outlined in the H.264 Video Encoding Guide -crf takes in values from 0 (lossless) to 51 (worst quality).
来源：https://stackoverflow.com/questions/49378977/ffmpeg-webm-to-mp4-quality-loss