ffmpeg xfade 不能很好地与 crossfade 配合使用

Posted 2023-02-25

【中文标题】ffmpeg xfade 不能很好地与 crossfade 配合使用

【英文标题】：ffmpeg xfade not working well with acrossfade

【发布时间】：2021-04-15 09:47:15

【问题描述】：

我在使用 xfade 和 crossfade 时遇到问题。

我有两个视频 t1.mp4 和 t2.mp4 具有相同的 fps、分辨率等。两个视频都是 15 秒长。

现在我想要在两者之间进行一秒钟的淡入淡出过渡。

没有交叉淡入，

ffmpeg -i t1.mp4 -i t2.mp4 -filter_complex "xfade=transition=fade:duration=1:offset=14,format=yuv420p" output.mp4

检查所有帧后，过渡看起来不错。有一些重叠的帧具有褪色效果。 请看下面两个连续的帧。

但结果的第二部分没有音频，这就是我决定使用 acrossfade 的原因。

ffmpeg -i t1.mp4 -i t2.mp4 -filter_complex "xfade=transition=fade:duration=1:offset=14,format=yuv420p;acrossfade=d=1" output.mp4

现在看来过渡效果不完整，有淡入淡出效果的重叠帧较少，过渡锐利。请看下面两个连续的帧，与上面相同的帧数。

请问我在这里错过了什么？

 ffmpeg -i t1.mp4 -i t2.mp4 -filter_complex "xfade=transition=fade:duration=1:offset=14,format=yuv420p;acrossfade=d=1" output.mp4
ffmpeg version 4.3.1-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 8 (Debian 8.3.0-6)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gmp --enable-libgme --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libdav1d --enable-libxvid --enable-libzvbi --enable-libzimg
  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
  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 't1.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:00:15.02, start: 0.000000, bitrate: 2447 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 2315 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 't2.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:00:15.02, start: 0.000000, bitrate: 1643 kb/s
    Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 1509 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Stream mapping:
  Stream #0:0 (h264) -> xfade:main
  Stream #0:1 (aac) -> acrossfade:crossfade0
  Stream #1:0 (h264) -> xfade:xfade
  Stream #1:1 (aac) -> acrossfade:crossfade1
  format -> Stream #0:0 (libx264)
  acrossfade -> Stream #0:1 (aac)
Press [q] to stop, [?] for help
[libx264 @ 0x5963dc0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x5963dc0] profile High, level 4.0, 4:2:0, 8-bit
[libx264 @ 0x5963dc0] 264 - core 161 r3018 db0d417 - 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=34 lookahead_threads=5 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: Video: h264 (libx264) (avc1 / 0x31637661), yuv420p(progressive), 1920x1080, q=-1--1, 25 fps, 12800 tbn, 25 tbc (default)
    Metadata:
      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: Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      encoder         : Lavc58.91.100 aac
frame=  726 fps= 69 q=-1.0 Lsize=    7114kB time=00:00:29.00 bitrate=2009.4kbits/s dup=1 drop=0 speed=2.76x    
video:6633kB audio:456kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.351093%
[libx264 @ 0x5963dc0] frame I:8     Avg QP:16.38  size: 96958
[libx264 @ 0x5963dc0] frame P:319   Avg QP:19.49  size: 14630
[libx264 @ 0x5963dc0] frame B:399   Avg QP:23.99  size:  3379
[libx264 @ 0x5963dc0] consecutive B-frames:  4.5% 63.6%  8.7% 23.1%
[libx264 @ 0x5963dc0] mb I  I16..4: 16.4% 61.0% 22.6%
[libx264 @ 0x5963dc0] mb P  I16..4:  3.5%  9.8%  0.7%  P16..4: 26.6%  4.9%  1.9%  0.0%  0.0%    skip:52.5%
[libx264 @ 0x5963dc0] mb B  I16..4:  0.3%  0.6%  0.2%  B16..8: 13.8%  0.9%  0.1%  direct: 0.9%  skip:83.1%  L0:44.1% L1:52.3% BI: 3.6%
[libx264 @ 0x5963dc0] 8x8 transform intra:67.2% inter:81.6%
[libx264 @ 0x5963dc0] coded y,uvDC,uvAC intra: 26.3% 38.2% 8.9% inter: 3.2% 5.8% 0.1%
[libx264 @ 0x5963dc0] i16 v,h,dc,p: 43% 25% 15% 17%
[libx264 @ 0x5963dc0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 34% 17% 37%  2%  2%  2%  2%  3%  2%
[libx264 @ 0x5963dc0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 29% 19% 14%  6%  7%  7%  6%  6%  5%
[libx264 @ 0x5963dc0] i8c dc,h,v,p: 60% 19% 18%  3%
[libx264 @ 0x5963dc0] Weighted P-Frames: Y:0.9% UV:0.9%
[libx264 @ 0x5963dc0] ref P L0: 69.4%  7.6% 17.5%  5.5%  0.0%
[libx264 @ 0x5963dc0] ref B L0: 85.1% 12.9%  2.1%
[libx264 @ 0x5963dc0] ref B L1: 99.0%  1.0%
[libx264 @ 0x5963dc0] kb/s:1870.80
[aac @ 0x58bb580] Qavg: 174.733

【问题讨论】：

有哪位ffmpeg大侠能帮帮我吗？

当过渡的持续时间和偏移发生在您的第一个视频结束之后，就会发生急剧过渡。您是否尝试过使用偏移量，更低？

【参考方案1】：

通过分离视频和音频轨道来修复。

ffmpeg -i t1.mp4 -i t2.mp4 -filter_complex "[0:v][1:v]xfade=transition=fadeblack:duration=1.000:offset=8.960,format=yuv420p[video];[0:a][1:a]acrossfade=d=1.000:c1=tri:c2=tri[audio]" -map [video] -map [audio] -movflags +faststart output.mp4

【参考方案2】：

我偶然发现了一个类似问题的open bug report，其中分离视频和音频并不能解决问题。

在这里，唯一可靠的解决方法是在另一个 ffmpeg 命令中将音频与视频完全分开处理，然后通过流复制将其合并，例如：

ffmpeg -i t1.mp4 -i t2.mp4 -filter_complex "[0:v][1:v]xfade=transition=fadeblack:duration=1.000:offset=8.960,format=yuv420p[video]" -an video.mp4
ffmpeg -i t1.mp4 -i t2.mp4 -filter_complex "[0:a][1:a]acrossfade=d=1.000:c1=tri:c2=tri[audio]" -vn audio.m4a
ffmpeg -i video.mp4 -i audio.m4a -c copy -movflags +faststart output.mp4

【讨论】：

或者再次输入输入并将该输入用作音频过滤器输入。