ffmpeg 保持帧率作为源

Question

我正在尝试使用 ffmpeg 在背景图像上叠加视频。但是与源视频相比，输出视频的帧率(25)和长度不同，我猜这是导致输出中视频和音频之间微小的不同步。如何调整命令以保持帧速率与源相同？

ffmpeg -i crop.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 'crop.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.76.100
  Duration: 00:02:26.10, start: 0.000000, bitrate: 1378 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1080x810, 1240 kb/s, 31.25 fps, 31.25 tbr, 16k tbn, 62.50 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

这是命令

/data/ffmpeg-4.4-amd64-static/ffmpeg -i background_image_crop.png -i crop.mp4 -filter_complex "[0:v][1:v]overlay=x=0:y=H/2-h/2" -c:a copy output.mp4
ffmpeg version 4.4-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2021 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. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, png_pipe, from 'background_image_crop.png':
  Duration: N/A, bitrate: N/A
  Stream #0:0: Video: png, rgb24(pc), 1080x1920, 25 fps, 25 tbr, 25 tbn, 25 tbc
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'crop.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.76.100
  Duration: 00:02:26.10, start: 0.000000, bitrate: 1378 kb/s
  Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1080x810, 1240 kb/s, 31.25 fps, 31.25 tbr, 16k tbn, 62.50 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:0 (png) -> overlay:main
  Stream #1:0 (h264) -> overlay:overlay
  overlay -> Stream #0:0 (libx264)
  Stream #1:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
[libx264 @ 0x57da140] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x57da140] profile High, level 4.0, 4:2:0, 8-bit
[libx264 @ 0x57da140] 264 - core 161 r3048 b86ae3c - H.264/MPEG-4 AVC codec - Copyleft 2003-2021 - 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=60 lookahead_threads=10 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:
    encoder         : Lavf58.76.100
  Stream #0:0: Video: h264 (avc1 / 0x31637661), yuv420p(tv, progressive), 1080x1920, q=2-31, 25 fps, 12800 tbn (default)
    Metadata:
      encoder         : Lavc58.134.100 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    : SoundHandler
      vendor_id       : [0][0][0][0]
frame= 3653 fps= 96 q=-1.0 Lsize=   24563kB time=00:02:26.07 bitrate=1377.5kbits/s dup=0 drop=911 speed=3.85x    
video:22143kB audio:2299kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.492343%
[libx264 @ 0x57da140] frame I:16    Avg QP:14.36  size:125240
[libx264 @ 0x57da140] frame P:989   Avg QP:17.65  size: 13266
[libx264 @ 0x57da140] frame B:2648  Avg QP:25.21  size:  2851
[libx264 @ 0x57da140] consecutive B-frames:  1.1%  4.3%  7.6% 87.1%
[libx264 @ 0x57da140] mb I  I16..4: 11.1% 72.4% 16.4%
[libx264 @ 0x57da140] mb P  I16..4:  2.6%  7.4%  0.6%  P16..4: 14.9%  4.4%  2.3%  0.0%  0.0%    skip:67.9%
[libx264 @ 0x57da140] mb B  I16..4:  0.3%  0.6%  0.0%  B16..8: 13.8%  1.0%  0.1%  direct: 0.4%  skip:83.8%  L0:43.9% L1:53.9% BI: 2.2%
[libx264 @ 0x57da140] 8x8 transform intra:69.0% inter:87.7%
[libx264 @ 0x57da140] coded y,uvDC,uvAC intra: 39.2% 62.5% 18.5% inter: 2.7% 4.8% 0.0%
[libx264 @ 0x57da140] i16 v,h,dc,p: 33% 27%  8% 32%
[libx264 @ 0x57da140] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 34% 19% 21%  4%  5%  5%  4%  5%  3%
[libx264 @ 0x57da140] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 34% 20% 10%  5%  8%  8%  6%  6%  3%
[libx264 @ 0x57da140] i8c dc,h,v,p: 49% 19% 25%  7%
[libx264 @ 0x57da140] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x57da140] ref P L0: 66.6% 10.3% 18.0%  5.1%
[libx264 @ 0x57da140] ref B L0: 91.4%  7.2%  1.4%
[libx264 @ 0x57da140] ref B L1: 96.8%  3.2%
[libx264 @ 0x57da140] kb/s:1241.39

Answer 1

对于您的示例是 31.25 fps，Richard 在代码开头使用参数 -r 作为 fps 值，如下所示

ffmpeg -r 31.25 -i background_image_crop.png -i crop.mp4 -filter_complex "[0:v][1:v]overlay=x=0:y=H/2-h/2" -c:a copy -preset ultrafast -movflags -faststart output.mp4

(我添加 -movflags -faststart 用于快速视频充电，并预设超快速以快速完成所有操作，仅用于此示例)

我已经探索了这个例子来获取下一个数据:

ffmpeg -i output.mp4

 Duration: 00:06:33.39, start: 0.000000, bitrate: 1523 kb/s
Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 640x480 [SAR 1:1 DAR 4:3], 1421 kb/s, 31.25 fps, 31.25 tbr, 16k tbn, 62.50 tbc (default)
Metadata:
  handler_name    : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 95 kb/s (default)
Metadata:
  handler_name    : SoundHandler