video - 使用 ffmpeg 组合小的 mp4 block ？

Question

我正在尝试使用 ffmpeg 将批量 png 图像转换为单个 mp4 x264 视频。由于我不会深入讨论的原因，转换将帧组转换为短的 mp4 block ，然后我想获取这些 block 并将它们以特定的 fps(在本例中为 30fps)合并到最终视频中。

我对 ffmpeg 和 x264 选项的理解太有限了，虽然我可以毫无问题地从源 png 帧生成单独的 mp4 block ，但最终的合并总是以复制和/或丢弃帧而告终，尤其是对于非常短的 block (< 4 帧)。

从 png 到 mp4 的转换使用以下命令:

ffmpeg -start_number 1001 -framerate 30 -f image2 -i 'intermediate.%d.png' -c:v libx264 -crf 1 -pix_fmt yuv420p -movflags +faststart -frames:v 4 -r 30 chunk.1.mp4 -y

这似乎按预期工作，我得到了一个可播放的 mp4 block ，在这种情况下，4 帧的 png 图像序列以 30fps。每个 block 的长度可以从 1 帧到大约 100 帧不等。

生成所有 block 后，我一直在尝试使用 concat demuxer 在不重新编码的情况下进行组合，将所有源 block 路径放在一个文件中:

连接.txt:

file 'chunk.1.mp4'
file 'chunk.2.mp4'
file 'chunk.3.mp4'
...

然后运行这个 ffmpeg 命令:

ffmpeg -f concat -i concat.txt -c:v copy merged.mp4 -y

但它在连接过程中这样说:

[concat @ 0x315ff80] 从比特率估计持续时间，这可能不准确

并且生成的 mp4 已丢失/重复帧。所以我尝试将持续时间信息添加到 concat.txt 文件中:

file 'chunk.1.mp4'
duration 0.133333
file 'chunk.2.mp4'
duration 0.133333
file 'chunk.3.mp4'
duration 0.066666

在这种情况下，两个 4 帧/30fps block 和一个 2 帧/30fps block 。这消除了那个估计警告，但结果仍然是重复/丢帧。

我不确定我在哪里出错了...在制作短 mp4 片段或在组合阶段我需要做什么才能以正确的帧速率获得单个 mp4 而没有重复或丢帧？

正如建议的那样，这是从 png->mp4 block 转换的控制台输出:

ffmpeg -loglevel verbose -start_number 1001 -framerate 30 -f image2 -i 'intermediate.%d.png' -c:v libx264 -crf 1 -pix_fmt yuv420p -movflags +faststart -frames:v 4 -r 30 chunk.1.mp4 -y
ffmpeg version 2.5.4 Copyright (c) 2000-2015 the FFmpeg developers
  built on Feb 26 2015 10:23:42 with gcc 4.4.7 (GCC) 20120313 (Red Hat 4.4.7-3)
  configuration: --prefix=/dept/srd/vendor/ffmpeg/bundle.rhel6/ffmpeg2.5.4 --enable-static --enable-pthreads --enable-gpl --enable-version3 --disable-ffserver --disable-ffplay --disable-ffprobe --enable-x11grab --enable-nonfree --extra-cflags=-I/dept/srd/vendor/ffmpeg/extern/rhel6/include --extra-ldflags=-L/dept/srd/vendor/ffmpeg/extern/rhel6/lib --enable-libx264 --enable-fontconfig --enable-libfreetype --enable-swscale --enable-libmp3lame --enable-libfaac --disable-yasm
  libavutil      54. 15.100 / 54. 15.100
  libavcodec     56. 13.100 / 56. 13.100
  libavformat    56. 15.102 / 56. 15.102
  libavdevice    56.  3.100 / 56.  3.100
  libavfilter     5.  2.103 /  5.  2.103
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, image2, from 'intermediate.%d.png':
  Duration: 00:00:00.27, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: png, rgba, 1024x1024 (0x0), 30 fps, 30 tbr, 30 tbn, 30 tbc
[graph 0 input from stream 0:0 @ 0x273e9c0] w:1024 h:1024 pixfmt:rgba tb:1/30 fr:30/1 sar:0/1 sws_param:flags=2
[auto-inserted scaler 0 @ 0x2737ea0] w:iw h:ih flags:'0x4' interl:0
[format @ 0x273ece0] auto-inserting filter 'auto-inserted scaler 0' between the filter 'Parsed_null_0' and the filter 'format'
[auto-inserted scaler 0 @ 0x2737ea0] w:1024 h:1024 fmt:rgba sar:0/1 -> w:1024 h:1024 fmt:yuv420p sar:0/1 flags:0x4
[libx264 @ 0x273c540] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0x273c540] profile High, level 3.2
[libx264 @ 0x273c540] 264 - core 142 - H.264/MPEG-4 AVC codec - Copyleft 2003-2014 - 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=36 lookahead_threads=6 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=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'chunk.1.mp4':
  Metadata:
    encoder         : Lavf56.15.102
    Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 1024x1024, q=-1--1, 30 fps, 15360 tbn, 30 tbc
    Metadata:
      encoder         : Lavc56.13.100 libx264
Stream mapping:
  Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
Press [q] to stop, [?] for help
No more output streams to write to, finishing.
[mp4 @ 0x273baa0] Starting second pass: moving the moov atom to the beginning of the file
frame=    4 fps=0.0 q=-1.0 Lsize=     197kB time=00:00:00.06 bitrate=24228.7kbits/s    
video:196kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.439751%
Input file #0 (intermediate.%d.png):
  Input stream #0:0 (video): 8 packets read (2341016 bytes); 5 frames decoded; 
  Total: 8 packets (2341016 bytes) demuxed
Output file #0 (chunk.3.mp4):
  Output stream #0:0 (video): 4 frames encoded; 4 packets muxed (201023 bytes); 
  Total: 4 packets (201023 bytes) muxed
[libx264 @ 0x273c540] frame I:1     Avg QP: 0.47  size:116049
[libx264 @ 0x273c540] frame P:1     Avg QP: 2.29  size: 37932
[libx264 @ 0x273c540] frame B:2     Avg QP: 2.37  size: 23184
[libx264 @ 0x273c540] consecutive B-frames: 25.0%  0.0% 75.0%  0.0%
[libx264 @ 0x273c540] mb I  I16..4: 80.0%  4.5% 15.5%
[libx264 @ 0x273c540] mb P  I16..4:  0.2%  0.1%  0.4%  P16..4:  8.1%  3.6%  3.7%  0.0%  0.0%    skip:83.9%
[libx264 @ 0x273c540] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  4.8%  1.2%  1.6%  direct: 4.3%  skip:88.1%  L0:38.6% L1:39.3% BI:22.1%
[libx264 @ 0x273c540] 8x8 transform intra:4.6% inter:14.8%
[libx264 @ 0x273c540] coded y,uvDC,uvAC intra: 20.7% 22.9% 22.8% inter: 8.7% 10.1% 10.0%
[libx264 @ 0x273c540] i16 v,h,dc,p: 95%  1%  3%  1%
[libx264 @ 0x273c540] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 21% 21% 22%  6%  6%  6%  7%  5%  6%
[libx264 @ 0x273c540] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 20% 17% 18%  7%  8%  7%  8%  6%  8%
[libx264 @ 0x273c540] i8c dc,h,v,p: 89%  4%  4%  3%
[libx264 @ 0x273c540] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x273c540] ref B L1: 89.5% 10.5%
[libx264 @ 0x273c540] kb/s:12020.88

正如我所说，这似乎产生了一个 30fps 的有效 mp4，输入图像中没有重复或丢失的帧。

这是合并阶段的输出:

ffmpeg -loglevel verbose -f concat -i concat.txt -c:v copy merged.mp4 -y
ffmpeg version 2.5.4 Copyright (c) 2000-2015 the FFmpeg developers
  built on Feb 26 2015 10:23:42 with gcc 4.4.7 (GCC) 20120313 (Red Hat 4.4.7-3)
  configuration: --prefix=/dept/srd/vendor/ffmpeg/bundle.rhel6/ffmpeg2.5.4 --enable-static --enable-pthreads --enable-gpl --enable-version3 --disable-ffserver --disable-ffplay --disable-ffprobe --enable-x11grab --enable-nonfree --extra-cflags=-I/dept/srd/vendor/ffmpeg/extern/rhel6/include --extra-ldflags=-L/dept/srd/vendor/ffmpeg/extern/rhel6/lib --enable-libx264 --enable-fontconfig --enable-libfreetype --enable-swscale --enable-libmp3lame --enable-libfaac --disable-yasm
  libavutil      54. 15.100 / 54. 15.100
  libavcodec     56. 13.100 / 56. 13.100
  libavformat    56. 15.102 / 56. 15.102
  libavdevice    56.  3.100 / 56.  3.100
  libavfilter     5.  2.103 /  5.  2.103
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, concat, from 'concat.txt':
  Duration: 00:00:00.67, start: 0.000000, bitrate: 2 kb/s
    Stream #0:0: Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1024x1024, 7791 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc
Output #0, mp4, to 'merged.mp4':
  Metadata:
    encoder         : Lavf56.15.102
    Stream #0:0: Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 1024x1024 (0x0), q=2-31, 7791 kb/s, 30 fps, 15360 tbn, 15360 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
No more output streams to write to, finishing.
frame=   20 fps=0.0 q=-1.0 Lsize=     748kB time=00:00:00.56 bitrate=10805.0kbits/s    
video:746kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.141687%
Input file #0 (concat.txt):
  Input stream #0:0 (video): 20 packets read (764361 bytes); 
  Total: 20 packets (764361 bytes) demuxed
Output file #0 (merged.mp4):
  Output stream #0:0 (video): 20 packets muxed (764361 bytes); 
  Total: 20 packets (764361 bytes) muxed

Answer 1

请包括您的控制台输出。

也就是说，出于好奇，您是否可以尝试使用连接过滤器并将所有这些组合到一个命令中，看看是否会改变任何东西。它看起来像这样:

ffmpeg -start_number 1001 -r 30 -i 'intermediate_1.%d.png' -i 'intermediate_2.%d.png' -i 'intermediate_3%d.png' -filter_complex "[0:v][1:v][2:v]concat=n=2:v=1:a=0[v]" -map [v] -c:v libx264 -pix_fmt yuv420p -movflags +faststart Output.mp4