我有一个使用案例,需要将 716x1280
的 mp4 视频缩小到 358x640
(原始大小的一半)。我使用的命令是:
ffmpeg -i ./input.mp4 -vf "scale=640:640:force_original_aspect_ratio=decrease,pad=ceil(iw/2)*2:ceil(ih/2)*2" ./output.mp4
在10个样本视频中,其中2个受到了色彩影响。下面我附上了受影响最严重的视频的比较。
注意:右侧的是原始视频中的一帧,左侧的是处理过(降低比例)的视频中的一帧。请注意图像中的红色和绿色(连皮肤颜色和头发颜色也被改变了)。
我想知道的是:
- 有没有办法防止这样的变化发生?可能是在饱和度、亮度、对比度或者其他参数上设置标记。
- 我假设ffmpeg在缩小视频时使用了一些默认设置。是什么让ffmpeg只为这两个视频更改颜色?如果它也对其他视频进行类似的更改,如何预测这种行为?
编辑:
我已尝试过的方法:
- 值为0和18的
-crf
。 - 如此处所述,使用
-preset veryslow
。
都没有帮助
Mediainfo输入VS输出
参数 | 输入 | 输出 |
---|---|---|
颜色范围 | 有限的 | NA(描述中没有该属性) |
色彩主体 | BT.2020 | NA(描述中没有该属性) |
传输特性 | HLG | NA(描述中没有该属性) |
矩阵系数 | BT.2020非常数 | NA(描述中没有该属性) |
位深度 | 8 | 8 |
ffmpeg命令日志
ffmpeg -i ./input.mp4 -vf "scale=640:640:force_original_aspect_ratio=decrease,pad=ceil(iw/2)*2:ceil(ih/2)*2" -movflags +faststart ./output.mp4
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
built with Apple clang version 12.0.0 (clang-1200.0.32.28)
configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1_9 --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-videotoolbox --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack
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, mov,mp4,m4a,3gp,3g2,mj2, from './input.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.45.100
Duration: 00:00:30.05, start: 0.000000, bitrate: 10366 kb/s
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt2020nc/bt2020/arib-std-b67), 716x1280, 10116 kb/s, 30 fps, 30 tbr, 19200 tbn, 38400 tbc (default)
Metadata:
handler_name : Core Media Video
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 245 kb/s (default)
Metadata:
handler_name : Core Media Audio
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x7faab4808800] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x7faab4808800] profile High, level 3.0, 4:2:0, 8-bit
[libx264 @ 0x7faab4808800] 264 - core 161 r3027 4121277 - H.264/MPEG-4 AVC codec - Copyleft 2003-2020 - 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=12 lookahead_threads=2 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 './output.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.45.100
Stream #0:0(und): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 358x640, q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)
Metadata:
handler_name : Core Media Video
encoder : Lavc58.91.100 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
handler_name : Core Media Audio
encoder : Lavc58.91.100 aac
[mp4 @ 0x7faab5808800] Starting second pass: moving the moov atom to the beginning of the file
frame= 901 fps=210 q=-1.0 Lsize= 3438kB time=00:00:30.02 bitrate= 938.0kbits/s speed=7.01x
video:2933kB audio:472kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.974633%
[libx264 @ 0x7faab4808800] frame I:6 Avg QP:22.60 size: 20769
[libx264 @ 0x7faab4808800] frame P:228 Avg QP:24.84 size: 7657
[libx264 @ 0x7faab4808800] frame B:667 Avg QP:27.59 size: 1697
[libx264 @ 0x7faab4808800] consecutive B-frames: 0.9% 0.9% 1.0% 97.2%
[libx264 @ 0x7faab4808800] mb I I16..4: 9.5% 64.6% 26.0%
[libx264 @ 0x7faab4808800] mb P I16..4: 2.5% 12.2% 2.5% P16..4: 37.2% 20.6% 11.2% 0.0% 0.0% skip:13.7%
[libx264 @ 0x7faab4808800] mb B I16..4: 0.4% 2.1% 0.2% B16..8: 42.2% 7.1% 1.2% direct: 1.8% skip:44.9% L0:39.4% L1:52.8% BI: 7.8%
[libx264 @ 0x7faab4808800] 8x8 transform intra:72.2% inter:74.2%
[libx264 @ 0x7faab4808800] coded y,uvDC,uvAC intra: 61.8% 67.2% 20.2% inter: 16.7% 13.9% 1.3%
[libx264 @ 0x7faab4808800] i16 v,h,dc,p: 24% 19% 7% 50%
[libx264 @ 0x7faab4808800] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 21% 16% 15% 6% 9% 11% 7% 10% 6%
[libx264 @ 0x7faab4808800] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 16% 13% 7% 9% 10% 7% 9% 4%
[libx264 @ 0x7faab4808800] i8c dc,h,v,p: 53% 16% 26% 5%
[libx264 @ 0x7faab4808800] Weighted P-Frames: Y:3.9% UV:1.8%
[libx264 @ 0x7faab4808800] ref P L0: 57.8% 19.5% 14.8% 7.8% 0.1%
[libx264 @ 0x7faab4808800] ref B L0: 90.7% 7.2% 2.1%
[libx264 @ 0x7faab4808800] ref B L1: 95.3% 4.7%
[libx264 @ 0x7faab4808800] kb/s:799.80
[aac @ 0x7faab2036a00] Qavg: 189.523
颜色范围
、颜色基本参数
、传输特性
和矩阵系数
。你能否使用Mediainfo工具,并发布input.mp4
和output.mp4
的这些参数?发布其他可能重要的参数,例如位深度
(如果不是8位)。 - Rotemffmpeg -i ./input.mp4 -vf "scale=640:640:force_original_aspect_ratio=decrease,pad=ceil(iw/2)*2:ceil(ih/2)*2" -vcodec libx264 -crf 17 -pix_fmt yuv420p ./output.mp4
- Rotem-vcodec libx264
并没有帮助。可能有所帮助的是-vcodec copy
。但是,流复制不支持filtergraph。 PS:如果我运行ffmpeg -i input.mp4 output.mp4
,可以参考上面的图像进行比较。但是,如果我运行ffmpeg -i -vcodec copy input.mp4 output.mp4
,输出视频将被修复,即输出视频中没有颜色变化。 - dravit