我正在尝试保存视频海康威视DS-2CD2032摄像机（又名 Swann HD-820CAM 又名 Lorex MCNB2151）通过 ffmpeg。它基本上使用如下命令：
$ ffmpeg -rtsp_transport tcp -i rtsp://user:pass@ip/ -c copy -map 0:0 driveway.mp4
ffmpeg version N-73641-gb90b6af Copyright (c) 2000-2015 the FFmpeg developers
built with gcc 4.9.1 (Ubuntu 4.9.1-16ubuntu6)
configuration:
libavutil 54. 28.100 / 54. 28.100
libavcodec 56. 48.100 / 56. 48.100
libavformat 56. 40.100 / 56. 40.100
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 21.100 / 5. 21.100
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 2.100 / 1. 2.100
Input #0, rtsp, from 'rtsp://user:pass@ip/':
Metadata:
title : Media Presentation
Duration: N/A, start: 0.466078, bitrate: N/A
Stream #0:0: Video: h264 (Main), yuv420p(tv, bt709), 1280x720, 15 fps, 15 tbr, 90k tbn, 30 tbc
Stream #0:1: Data: none
[mp4 @ 0x24f6720] Codec for stream 0 does not use global headers but container format requires global headers
Output #0, mp4, to 'driveway.mp4':
Metadata:
title : Media Presentation
encoder : Lavf56.40.100
Stream #0:0: Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 1280x720, q=2-31, 15 fps, 15 tbr, 90k tbn, 90k tbc
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
[mp4 @ 0x24f6720] Non-monotonous DTS in output stream 0:0; previous: 0, current: -30013; changing to 1. This may result in incorrect timestamps in the output file.
[mp4 @ 0x24f6720] Non-monotonous DTS in output stream 0:0; previous: 1, current: -23990; changing to 2. This may result in incorrect timestamps in the output file.
[mp4 @ 0x24f6720] Non-monotonous DTS in output stream 0:0; previous: 2, current: -17996; changing to 3. This may result in incorrect timestamps in the output file.
[mp4 @ 0x24f6720] Non-monotonous DTS in output stream 0:0; previous: 3, current: -11994; changing to 4. This may result in incorrect timestamps in the output file.
[mp4 @ 0x24f6720] Non-monotonous DTS in output stream 0:0; previous: 4, current: -5992; changing to 5. This may result in incorrect timestamps in the output file.
[mp4 @ 0x24f6720] Non-monotonous DTS in output stream 0:0; previous: 5, current: -18; changing to 6. This may result in incorrect timestamps in the output file.
frame= 178 fps= 18 q=-1.0 Lsize= 1711kB time=00:00:11.39 bitrate=1229.3kbits/s
video:1708kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.177573%
但我担心警告信息。特别是，我想解决可能导致视频播放不流畅或与某些播放器交互不顺畅的任何问题。所以...
- 什么是“全局标头”？缺少它们会有什么后果？我在ffmpeg 比特流过滤器文档。如果我添加它描述的“-flags:v +global_header -bsf:v dump_extra”，警告就会消失。它到底在做什么？我猜它会将某些内容从每个数据包的标头移动到全局标头？我该如何检查这些/观察差异？
- 如果有的话，我能对“非单调 DTS”警告做些什么呢？
fwiw，我用 libavformat 编写了一个自定义程序，它从每个帧转储 DTS 信息，如下所示：
while (av_read_frame(input_context, &packet) == 0) {
if (packet.flags & AV_PKT_FLAG_KEY) {
cout << "have key frame, dts: " << packet.dts << endl;
} else {
cout << " have non-key frame, dts: " << packet.dts << endl;
}
}
然后它就输出了这些，所以我猜只是关键帧的 dts 不正确？不知道该怎么解释。
have key frame, dts: 41995
have non-key frame, dts: 12033
have non-key frame, dts: 17966
have key frame, dts: 23970
have non-key frame, dts: 29992
have non-key frame, dts: 35992
have non-key frame, dts: 41995
have non-key frame, dts: 47995
have key frame, dts: 53973
have non-key frame, dts: 59994
have non-key frame, dts: 65996
have non-key frame, dts: 71995
have non-key frame, dts: 77994
have key frame, dts: 83978
have non-key frame, dts: 89993
have non-key frame, dts: 95997
have non-key frame, dts: 102035
have non-key frame, dts: 107978
have key frame, dts: 113976
have non-key frame, dts: 119998
have non-key frame, dts: 126000
have non-key frame, dts: 131997
have non-key frame, dts: 138000