saving standard-compliant video from Hikvision DS-2CD2032 cameras

Question

I'm trying to save video from Hikvision DS-2CD2032 cameras (aka Swann HD-820CAM aka Lorex MCNB2151) via ffmpeg. It basically works with a command like this:

$ 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%

but I'm concerned about the warning messages. In particular, I want to address any problem that might make the video not play smoothly or not interact well with some players. So...

1. What are "global headers"? What are the consequences of them being missing? I found a note about dump_extra in the ffmpeg bitstream filters documentation. If I add the "-flags:v +global_header -bsf:v dump_extra" it describes, the warning goes away. What is it doing exactly? I gather it moves something from a per-packet header to a global header? How would I examine these / observe the difference?
2. What, if anything, can I do about the "Non-monotonous DTS" warnings?

fwiw, I wrote a custom program with libavformat which dumped the DTS info from each frame as follows:

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;
  }
}

and it spit out this, so I guess it's just the key frames that have the incorrect dts? Dunno what to make of that.

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