问题描述
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，输出视频具有不同的帧率（25）和长度，我想这会导致输出中视频和音频之间的微小不同步。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,bitrate: 1378 kb/s
Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661),62.50 tbc (default)
Metadata:
handler_name : VideoHandler
vendor_id : [0][0][0][0]
Stream #1:1(und): Audio: aac (LC) (mp4a / 0x6134706D),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,to 'output.mp4':
Metadata:
encoder : Lavf58.76.100
Stream #0:0: Video: h264 (avc1 / 0x31637661),progressive),q=2-31,12800 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),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,ddl,ddr,vr,hd,vl,hu: 34% 19% 21% 4% 5% 5% 4% 5% 3%
[libx264 @ 0x57da140] i4 v,hu: 34% 20% 10% 5% 8% 8% 6% 6% 3%
[libx264 @ 0x57da140] i8c dc,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
解决方法
对于您的示例是 31.25 fps，Richard 在代码的开头使用参数 -r 作为 fps 值，就像这样
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
（我加了-movflags -faststart 是为了快速充电，并预设了ultrafast 来做所有的快速，只针对这个例子）
我已经探索了这个获取下一个数据的例子：
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