使用FFMPEG尽可能快地从流视频中保存帧

Question

我正在从GoPro相机中捕获流视频中的单个帧。这主要是要快速了解我的主题是否在录制视频和 /或图片之前就在框架中。该框架很快捕获，但随后FFMPEG似乎需要将近10秒的时间才能“吐出”。我已经砍了好几天了，没有取得太大的进步。命令行现在：

fmpeg -loglevel verbose -y -i udp://@0.0.0.0:8554 -f image2 -map 0:0 -map -0:1 -map -0:2 -map -0:3 -flush_packets 1 -blocksize 2048 -c:v mjpeg  -qscale:v 8 -frames:v 1 -vf "select='eq(pict_type\,I)'"  test_%03d.jpg

-loglevel verbose : tell me everything
-y : overwrite existing files 
-i udp://@0.0.0.0:8554 : input is a stream at this address
-f image2 : extract an image 
-map 0:0 -map -0:1 -map -0:2 -map -0:3 : ignore all streams except 0
-flush_packets 1 : attempt to say "don't buffer" 
-blocksize 2048 : blocksize made really small to get files to write 
-c:v mjpeg : output is a jpeg  
-qscale:v 8 : output quality 8 
-frames:v 1 : give me 1 frame 
-vf "select='eq(pict_type\,I)'" give me only key frames 
test_%03d.jpg : output file format

它有效，输出就像：

ffmpeg version 3.4.8-0ubuntu0.2 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 7 (Ubuntu 7.5.0-3ubuntu1~18.04)
  configuration: --prefix=/usr --extra-version=0ubuntu0.2 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
[mpegts @ 0x55d3e049ab00] parser not found for codec none, packets or times may be invalid.
[h264 @ 0x55d3e04bffe0] non-existing PPS 0 referenced
    Last message repeated 1 times
[h264 @ 0x55d3e04bffe0] decode_slice_header error
[h264 @ 0x55d3e04bffe0] no frame!
[h264 @ 0x55d3e04bffe0] non-existing PPS 0 referenced
    Last message repeated 1 times
[h264 @ 0x55d3e04bffe0] decode_slice_header error
[h264 @ 0x55d3e04bffe0] no frame!
[h264 @ 0x55d3e04bffe0] non-existing PPS 0 referenced
    Last message repeated 1 times
[h264 @ 0x55d3e04bffe0] decode_slice_header error
[h264 @ 0x55d3e04bffe0] no frame!
[h264 @ 0x55d3e04bffe0] non-existing PPS 0 referenced
    Last message repeated 1 times
[h264 @ 0x55d3e04bffe0] decode_slice_header error
[h264 @ 0x55d3e04bffe0] no frame!
[h264 @ 0x55d3e04bffe0] Reinit context to 1280x720, pix_fmt: yuvj420p

---------- 8秒乘坐---------------------------------

[mpegts @ 0x55d3e049ab00] max_analyze_duration 7000000 reached at 7018667 microseconds st:1
[mpegts @ 0x55d3e049ab00] Could not find codec parameters for stream 2 (Unknown: none ([128][0][0][0] / 0x0080)): unknown codec
Consider increasing the value for the 'analyzeduration' and 'probesize' options
[mpegts @ 0x55d3e049ab00] Could not find codec parameters for stream 3 (Audio: ac3 ([129][0][0][0] / 0x0081), 0 channels, fltp): unspecified sample rate
Consider increasing the value for the 'analyzeduration' and 'probesize' options
Input #0, mpegts, from 'udp://@0.0.0.0:8554':
  Duration: N/A, start: 399.253333, bitrate: N/A
  Program 1
    Stream #0:0[0x1011]: Video: h264 (High), 1 reference frame ([27][0][0][0] / 0x001B), yuvj420p(pc, bt709, progressive, left), 1280x720 [SAR 1:1 DAR 16:9], 29.97 fps, 29.97 tbr, 90k tbn, 180k tbc
    Stream #0:1[0x1100]: Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, stereo, fltp, 189 kb/s
    Stream #0:2[0x200]: Unknown: none ([128][0][0][0] / 0x0080)
    Stream #0:3[0x201]: Audio: ac3 ([129][0][0][0] / 0x0081), 0 channels, fltp
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> mjpeg (native))
Press [q] to stop, [?] for help
[mpegts @ 0x55d3e049ab00] Correcting start time by 12200
[h264 @ 0x55d3e05c5260] Reinit context to 1280x720, pix_fmt: yuvj420p
[h264 @ 0x55d3e0582720] reference picture missing during reorder
[h264 @ 0x55d3e0582720] Missing reference picture, default is 65531
[h264 @ 0x55d3e050fa80] reference picture missing during reorder
[h264 @ 0x55d3e050fa80] Missing reference picture, default is 65532
[h264 @ 0x55d3e05203e0] mmco: unref short failure
[graph 0 input from stream 0:0 @ 0x55d3e049a6e0] w:1280 h:720 pixfmt:yuvj420p tb:1/90000 fr:30000/1001 sar:1/1 sws_param:flags=2
Output #0, image2, to 'test_%03d.jpg':
  Metadata:
    encoder         : Lavf57.83.100
    Stream #0:0: Video: mjpeg, 1 reference frame, yuvj420p(pc, left), 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 29.97 fps, 29.97 tbn, 29.97 tbc
    Metadata:
      encoder         : Lavc57.107.100 mjpeg
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
*** 4 dup!
    Last message repeated 1 times
No more output streams to write to, finishing.
frame=   10 fps=0.0 q=8.0 Lsize=N/A time=00:00:00.33 bitrate=N/A dup=9 drop=1 speed=5.96x
video:416kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Input file #0 (udp://@0.0.0.0:8554):
  Input stream #0:0 (video): 23 packets read (367296 bytes); 12 frames decoded;
  Input stream #0:1 (audio): 39 packets read (19992 bytes);
  Input stream #0:2 ((null)): 0 packets read (0 bytes);
  Input stream #0:3 (audio): 0 packets read (0 bytes);
  Total: 62 packets (387288 bytes) demuxed
Output file #0 (test_%03d.jpg):
  Output stream #0:0 (video): 10 frames encoded; 10 packets muxed (426390 bytes);
  Total: 10 packets (426390 bytes) muxed

我从脚本启动时立即从。

知道为什么会这么久？

有什么方法可以加快速度？

即使我可以拿出一秒钟并继续前进，这也将是很棒的。我的程序只能查看最新图像。但是，由于它仅在运行结束时吐出框架，这对我没有帮助。