我正在尝试将mp4文件合并成一个文件。我正尝试直接使用concat过滤器，原因与此问题无关（因此-i list.txt不是有效解决方案）。所有涉及的视频文件长度都在4到20分钟之间。
我正在执行的操作：
% ffmpeg -i f01.mp4 -i f02.mp4 -filter_complex "[0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1[v][a]" -map "[v]" -map "[a]" output.mp4
ffmpeg检查每个流的元数据，然后开始处理并输出大量信息。经过短暂时间（几秒钟或一分钟左右，似乎与第一个视频的持续时间成比例），我开始看到像这样的消息:More than 1000 frames duplicated
More than 10000 frames duplicated 512kB time=00:00:00.12 bitrate=32771.0kbits/s dup=33365 drop=0 speed=0.00449x
More than 100000 frames duplicated 1280kB time=00:00:00.17 bitrate=61442.1kbits/s dup=66730 drop=0 speed=0.00272x
...然后这个进程就永远不会完成。如果我让电脑持续运行24小时，ffmpeg仍然使用最大可用的CPU（200-300%）。输出文件只有48字节。
注意：输入文件各自只有几分钟，因此逐个重新编码每个文件只需要几分钟。
注意：如果我将命令更改为在源0和源1中都使用f01.mp4，则命令会在不到5分钟内按预期完成：
% # example that works:
% # note, however, that this just repeats the same source twice
% ffmpeg -i f01.mp4 -i f01.mp4 -filter_complex "[0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1[v][a]" -map "[v]" -map "[a]" output.mp4
完整输出：
以下是运行的完整输出，希望能有所帮助：
% ffmpeg -i f01.mp4 -i f02.mp4 -filter_complex "[0:v][0:a][1:v][1:a]concat=n=2:v=1:a=1[v][a]" -map "[v]" -map "[a]" output.mp4
ffmpeg version 4.3 Copyright (c) 2000-2020 the FFmpeg developers
built with Apple clang version 11.0.3 (clang-1103.0.32.62)
configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3_2 --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-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 --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 'f01.mp4':
Metadata:
major_brand : mp42
minor_version : 512
compatible_brands: isomiso2avc1mp41
creation_time : 2020-06-04T21:34:26.000000Z
encoder : HandBrake 1.3.2 2020050300
Duration: 00:04:14.66, start: 0.000000, bitrate: 525 kb/s
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, smpte170m/smpte170m/bt709), 708x478 [SAR 8:9 DAR 944:717], 366 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 180k tbc (default)
Metadata:
creation_time : 2020-06-04T21:34:26.000000Z
handler_name : VideoHandler
Stream #0:1(jpn): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 149 kb/s (default)
Metadata:
creation_time : 2020-06-04T21:34:26.000000Z
handler_name : Stereo
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'f02.mp4':
Metadata:
major_brand : mp42
minor_version : 512
compatible_brands: isomiso2avc1mp41
creation_time : 2020-06-04T21:38:15.000000Z
encoder : HandBrake 1.3.2 2020050300
Duration: 00:06:30.95, start: 0.000000, bitrate: 1328 kb/s
Stream #1:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, smpte170m/smpte170m/bt709), 708x478 [SAR 8:9 DAR 944:717], 1179 kb/s, 29.97 fps, 30 tbr, 90k tbn, 180k tbc (default)
Metadata:
creation_time : 2020-06-04T21:38:15.000000Z
handler_name : VideoHandler
Stream #1:1(jpn): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 140 kb/s (default)
Metadata:
creation_time : 2020-06-04T21:38:15.000000Z
handler_name : Stereo
File 'output.mp4' already exists. Overwrite? [y/N] y
Stream mapping:
Stream #0:0 (h264) -> concat:in0:v0
Stream #0:1 (aac) -> concat:in0:a0
Stream #1:0 (h264) -> concat:in1:v0
Stream #1:1 (aac) -> concat:in1:a0
concat:out:v0 -> Stream #0:0 (libx264)
concat:out:a0 -> Stream #0:1 (aac)
Press [q] to stop, [?] for help
[mp4 @ 0x7ff130014000] Frame rate very high for a muxer not efficiently supporting it.
Please consider specifying a lower framerate, a different muxer or -vsync 2
[libx264 @ 0x7ff130021200] using SAR=8/9
[libx264 @ 0x7ff130021200] MB rate (1350000000) > level limit (16711680)
[libx264 @ 0x7ff130021200] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x7ff130021200] profile High, level 6.2, 4:2:0, 8-bit
[libx264 @ 0x7ff130021200] 264 - core 160 r3011 cde9a93 - 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=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 'output.mp4':
Metadata:
major_brand : mp42
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.45.100
Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv420p(progressive), 708x478 [SAR 8:9 DAR 944:717], q=-1--1, 1000k tbn, 1000k 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), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
encoder : Lavc58.91.100 aac
More than 1000 frames duplicated
More than 10000 frames duplicated 512kB time=00:00:00.12 bitrate=32771.0kbits/s dup=33365 drop=0 speed=0.00449x
More than 100000 frames duplicated 1280kB time=00:00:00.17 bitrate=61442.1kbits/s dup=66730 drop=0 speed=0.00272x
frame=667333 fps=1079 q=33.0 size= 14848kB time=00:00:00.76 bitrate=158379.2kbits/s dup=667312 drop=0 speed=0.00124x
vsync 2不会影响视频质量。 - Gyan