我的公司有一批我们分销的 IP 摄像头 - 特别是 Grandstream - 制造商已更改了其固件。ffmpeg 用于 rtsp 流的正常 keepalive（ff_rtsp_send_cmd_async(s, "GET_PARAMETER", rt->control_uri, NULL); 或 ff_rtsp_send_cmd_async(s, "OPTIONS", "*", NULL); 均位于 libavformat/rtspdec.c 中）不再起作用，原因有两个：
1) 新的 Grandstream 固件现在正在检查接收器报告以确定读取流的程序是否实时，而不仅仅是任何东西。
2) 新的 Grandstream 固件要求接收器报告保持连接至少每 25 秒发生一次，而在音频流上，它目前仅每 30 秒左右发生一次（视频每 7 秒左右获得一次）。
因此，在 ffmpeg 连接约一分钟后，摄像机停止发送音频流，ffmpeg 上的音频流读取文件结束，然后 ffmpeg 关闭所有内容。
由于我无法更改固件，我试图深入研究 ffmpeg 代码，使其发送适当的接收器报告以保持活动状态……但我一无所获。我在接收器报告中添加了一小段代码，因此当我在调试时调用 ffmpeg 时，我知道它们何时运行，但是……嗯，进展不顺利。
测试命令：ffmpeg -loglevel debug -i rtsp://admin:[电子邮件保护]:554/0 -acodec libmp3lame -ar 22050 -vcodec 复制 -y -f flv /dev/null &> test.txt
测试输出：
`[root@localhost ffmpeg]# cat test.txt
ffmpeg version 2.0 Copyright (c) 2000-2013 the FFmpeg developers
built on Aug 21 2013 14:24:28 with gcc 4.4.7 (GCC) 20120313 (Red Hat 4.4.7-3)
configuration: --datadir=/usr/share/ffmpeg --bindir=/usr/local/bin --libdir=/usr/local/lib --incdir=/usr/local/include --shlibdir=/usr/lib --mandir=/usr/share/man --disable-avisynth --extra-cflags='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables' --enable-avfilter --enable-libx264 --enable-gpl --enable-version3 --enable-postproc --enable-pthreads --enable-shared --enable-swscale --enable-vdpau --enable-x11grab --enable-librtmp --enable-libopencore-amrnb --enable-libopencore-amrwb --disable-static --enable-libgsm --enable-libxvid --enable-libvpx --enable-libvorbis --enable-libvo-aacenc --enable-libmp3lame
libavutil 52. 38.100 / 52. 38.100
libavcodec 55. 18.102 / 55. 18.102
libavformat 55. 12.100 / 55. 12.100
libavdevice 55. 3.100 / 55. 3.100
libavfilter 3. 79.101 / 3. 79.101
libswscale 2. 3.100 / 2. 3.100
libswresample 0. 17.102 / 0. 17.102
libpostproc 52. 3.100 / 52. 3.100
Splitting the commandline.
Reading option '-loglevel' ... matched as option 'loglevel' (set logging level) with argument 'debug'.
Reading option '-i' ... matched as input file with argument 'rtsp://admin:[email protected]:554/0'.
Reading option '-acodec' ... matched as option 'acodec' (force audio codec ('copy' to copy stream)) with argument 'libmp3lame'.
Reading option '-ar' ... matched as option 'ar' (set audio sampling rate (in Hz)) with argument '22050'.
Reading option '-vcodec' ... matched as option 'vcodec' (force video codec ('copy' to copy stream)) with argument 'copy'.
Reading option '-y' ... matched as option 'y' (overwrite output files) with argument '1'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'flv'.
Reading option '/dev/null' ... matched as output file.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option loglevel (set logging level) with argument debug.
Applying option y (overwrite output files) with argument 1.
Successfully parsed a group of options.
Parsing a group of options: input file rtsp://admin:[email protected]:554/0.
Successfully parsed a group of options.
Opening an input file: rtsp://admin:[email protected]:554/0.
[rtsp @ 0x9d9ccc0] SDP:
v=0
o=StreamingServer 3331435948 1116907222000 IN IP4 192.168.4.3
s=h264.mp4
c=IN IP4 0.0.0.0
t=0 0
a=control:*
m=video 0 RTP/AVP 96
a=control:trackID=0
a=rtpmap:96 H264/90000
a=fmtp:96 packetization-mode=1; sprop-parameter-sets=Z0LgHtoCgPRA,aM4wpIA=
m=audio 0 RTP/AVP 0
a=control:trackID=1
a=rtpmap:0 PCMU/8000
a=ptime:20
m=application 0 RTP/AVP 107
a=control:trackID=2
a=rtpmap:107 vnd.onvif.metadata/90000
[rtsp @ 0x9d9ccc0] video codec set to: h264
[NULL @ 0x9d9f400] RTP Packetization Mode: 1
[NULL @ 0x9d9f400] Extradata set to 0x9d9f900 (size: 22)!
[rtsp @ 0x9d9ccc0] audio codec set to: pcm_mulaw
[rtsp @ 0x9d9ccc0] audio samplerate set to: 8000
[rtsp @ 0x9d9ccc0] audio channels set to: 1
[rtsp @ 0x9d9ccc0] hello state=0
[h264 @ 0x9d9f400] Current profile doesn't provide more RBSP data in PPS, skipping
Last message repeated 1 times
[rtsp @ 0x9d9ccc0] All info found
Guessed Channel Layout for Input Stream #0.1 : mono
Input #0, rtsp, from 'rtsp://admin:[email protected]:554/0':
Metadata:
title : h264.mp4
Duration: N/A, start: 0.000000, bitrate: 64 kb/s
Stream #0:0, 28, 1/90000: Video: h264 (Constrained Baseline), yuv420p, 640x480, 1/180000, 10 tbr, 90k tbn, 180k tbc
Stream #0:1, 156, 1/8000: Audio: pcm_mulaw, 8000 Hz, mono, s16, 64 kb/s
Successfully opened the file.
Parsing a group of options: output file /dev/null.
Applying option acodec (force audio codec ('copy' to copy stream)) with argument libmp3lame.
Applying option ar (set audio sampling rate (in Hz)) with argument 22050.
Applying option vcodec (force video codec ('copy' to copy stream)) with argument copy.
Applying option f (force format) with argument flv.
Successfully parsed a group of options.
Opening an output file: /dev/null.
Successfully opened the file.
detected 2 logical cores
[graph 0 input from stream 0:1 @ 0x9f15380] Setting 'time_base' to value '1/8000'
[graph 0 input from stream 0:1 @ 0x9f15380] Setting 'sample_rate' to value '8000'
[graph 0 input from stream 0:1 @ 0x9f15380] Setting 'sample_fmt' to value 's16'
[graph 0 input from stream 0:1 @ 0x9f15380] Setting 'channel_layout' to value '0x4'
[graph 0 input from stream 0:1 @ 0x9f15380] tb:1/8000 samplefmt:s16 samplerate:8000 chlayout:0x4
[audio format for output stream 0:1 @ 0x9efa7c0] Setting 'sample_fmts' to value 's32p|fltp|s16p'
[audio format for output stream 0:1 @ 0x9efa7c0] Setting 'sample_rates' to value '22050'
[audio format for output stream 0:1 @ 0x9efa7c0] Setting 'channel_layouts' to value '0x4|0x3'
[audio format for output stream 0:1 @ 0x9efa7c0] auto-inserting filter 'auto-inserted resampler 0' between the filter 'Parsed_anull_0' and the filter 'audio format for output stream 0:1'
[AVFilterGraph @ 0x9f15980] query_formats: 4 queried, 9 merged, 3 already done, 0 delayed
[auto-inserted resampler 0 @ 0x9dfada0] ch:1 chl:mono fmt:s16 r:8000Hz -> ch:1 chl:mono fmt:s16p r:22050Hz
Output #0, flv, to '/dev/null':
Metadata:
title : h264.mp4
encoder : Lavf55.12.100
Stream #0:0, 0, 1/1000: Video: h264 ([7][0][0][0] / 0x0007), yuv420p, 640x480, 1/90000, q=2-31, 1k tbn, 90k tbc
Stream #0:1, 0, 1/1000: Audio: mp3 (libmp3lame) ([2][0][0][0] / 0x0002), 22050 Hz, mono, s16p
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Stream #0:1 -> #0:1 (pcm_mulaw -> libmp3lame)
Press [q] to stop, [?] for help
Current profile doesn't provide more RBSP data in PPS, skippingrate= 135.4kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 134.4kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 135.0kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 135.5kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 136.9kbits/s
Queue input is backward in time= 233kB time=00:00:13.69 bitrate= 139.4kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 136.3kbits/s
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 13926; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 13952; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 13979; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14005; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14031; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14057; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14083; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14109; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14135; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14161; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14188; changing to 14239. This may result in incorrect timestamps in the output file.
[flv @ 0x9de1200] Non-monotonous DTS in output stream 0:1; previous: 14239, current: 14214; changing to 14239. This may result in incorrect timestamps in the output file.
Current profile doesn't provide more RBSP data in PPS, skippingrate= 141.5kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 142.0kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 142.5kbits/s
Receiver Report delay: 469789, gettime: -1527669086, last_recep: 322446, timebase: -1534837492
Current profile doesn't provide more RBSP data in PPS, skippingrate= 141.5kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 141.7kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 141.1kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 140.6kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 140.7kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.9kbits/s
Receiver Report delay: 132993, gettime: -1516538925, last_recep: 322446, timebase: -1518568234
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.6kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.6kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.7kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.4kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 140.0kbits/s
Receiver Report delay: 897727, gettime: -1504870331, last_recep: 322446, timebase: -1518568552
[NULL @ 0x9d9f400] Current profile doesn't provide more RBSP data in PPS, skipping
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.4kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.1kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.0kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 139.0kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 138.6kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 138.5kbits/s
Current profile doesn't provide more RBSP data in PPS, skippingrate= 138.2kbits/s
EOF on sink link output stream 0:1:default.time=00:00:58.40 bitrate= 139.6kbits/s
No more output streams to write to, finishing.
[libmp3lame @ 0x9dfa580] Trying to remove 344 more samples than there are in the queue
frame= 589 fps= 11 q=-1.0 Lsize= 1003kB time=00:00:58.85 bitrate= 139.5kbits/s
video:724kB audio:231kB subtitle:0 global headers:0kB muxing overhead 4.955356%
2959 frames successfully decoded, 0 decoding errors
[AVIOContext @ 0x9e021c0] Statistics: 3 seeks, 2860 writeouts
[root@localhost ffmpeg]#
答案1
而且……我想我找到了。能把这当成一份全职工作真是太有趣了。我现在正在做一些测试，但我肯定已经超过了我之前设定的一分钟阈值（超出了很多——在我输入这些文字时，我已经用了一个小时 45 分钟了）：
在 libavformat/rtpdec.c 的 ff_rtp_check_and_send_back_rr 函数中，有一行写着“rtcp_bytes /= 50;” - 这个数字似乎控制着它发送接收器报告的频率。降低这个数字会使它更频繁地发生。