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为什么 ffmpeg 在录制 rtsp 源时会记录错误的 FPS？

tag-icon • tag-icon linux video ffmpeg streaming rtsp
为什么 ffmpeg 在录制 rtsp 源时会记录错误的 FPS？

我正在使用 Raspberry Pi 3B+ 录制 ActiA31 安全摄像头（通过以太网供电路由器连接）的视频。摄像头设置为以 29.97 fps 录制。我使用的命令是

sudo /usr/local/bin/ffmpeg -i rtsp://username:pwd@IPaddress -t 10 -vcodec copy -acodec copy outputfile.mp4

视频确实录制了，但录制视频的元数据显示帧速率 (fps) 略有不同。输出如下（使用 ffprobe）：

Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709), 2048x1536, 12074 kb/s, 30.02 fps, 29.97 tbr, 90k tbn, 180k tbc (default)

为什么 fps 与 tbr 不同？

我已将原始 ffmpeg 命令的输出复制到此处，希望它能帮助解决问题。我尝试使用选项“-use_wallclock_as_timestamps 1”，但结果并没有什么不同。我正在使用视频进行速度分析，需要帧速率与摄像机录制的帧速率完全相同，因此我无法设置自己的帧速率。我还收到一些“无效 NAL”错误，但从我在 stackexchange 上看到的情况来看，这些错误似乎很常见。

pi@raspberrypi:~/lspiv/scripts $ ffmpeg version N-94564-gaac382e9e5 Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 8 (Raspbian 8.3.0-6+rpi1)
  configuration: --arch=armel --target-os=linux --enable-gpl --enable-libx264 --enable-nonfree
  libavutil      56. 33.100 / 56. 33.100
  libavcodec     58. 55.100 / 58. 55.100
  libavformat    58. 30.100 / 58. 30.100
  libavdevice    58.  9.100 / 58.  9.100
  libavfilter     7. 58.100 /  7. 58.100
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
[h264 @ 0x1e31790] Invalid NAL unit 0, skipping.
[h264 @ 0x1e31790] Invalid NAL unit 8, skipping.
    Last message repeated 5 times
[h264 @ 0x1e329e0] Invalid NAL unit 0, skipping.
[h264 @ 0x1e329e0] Invalid NAL unit 8, skipping.
    Last message repeated 1 times
[h264 @ 0x1e329e0] Invalid NAL unit 0, skipping.
[h264 @ 0x1e329e0] Invalid NAL unit 8, skipping.
[rtsp @ 0x1e2e390] decoding for stream 1 failed
Input #0, rtsp, from 'rtsp://username:pwd@IPaddress':
  Metadata:
    title           : Video Server Session
  Duration: N/A, start: 0.033344, bitrate: N/A
    Stream #0:0: Video: h264 (High), yuvj420p(pc, bt709, progressive), 2048x1536, 59.94 tbr, 90k tbn, 180k tbc
    Stream #0:1: Video: h264 (High), yuvj420p(pc, bt709, progressive), 320x240, 90k tbr, 90k tbn, 180k tbc
Output #0, mp4, to '/home/pi/lspiv/video_ops/saved_videos/19860501_20200226_112619.mp4':
  Metadata:
    title           : Video Server Session
    encoder         : Lavf58.30.100
    Stream #0:0: Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709, progressive), 2048x1536, q=2-31, 59.94 tbr, 90k tbn, 90k tbc
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
[mp4 @ 0x1e90670] Timestamps are unset in a packet for stream 0. This is deprecated and will stop working in the future. Fix your code to set the timestamps properly
[mp4 @ 0x1e90670] Non-monotonous DTS in output stream 0:0; previous: 0, current: 0; changing to 1. This may result in incorrect timestamps in the output file.
frame=  301 fps= 63 q=-1.0 Lsize=     412kB time=00:00:09.99 bitrate= 337.9kbits/s speed=2.09x
video:409kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.871962%

答案1

您是否尝试过使用输入选项-r？

ffmpeg -r 30 -i rtsp://...

或29,97

ffmpeg -r 30000/1001 -i rtsp://...

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