Hello, I need a TS stream containing two camera angles from two IP encoders supporting RTSP. Both encoders share the same time by using a local NTP server. I used ffmpeg command like "ffmpeg -i rtsp://<encoder1> -i rtsp://<encoder2> -c copy -y filename.ts", and noticed that the second track in the ts file is always 2-3 seconds behind. I even tried multiple tracks with the same encoder as the command and logs below, but still far away to be synchronized. Please advise if there is a way to obtain synchronized video tracks from IP encoders. Thanks! ----------------- command & log ---------------------- $ ffmpeg -v debug -thread_queue_size 512 -rtsp_transport tcp -i rtsp:// 192.168.1.20/stream -thread_queue_size 512 -rtsp_transport tcp -allowed_media_types video -i rtsp://192.168.1.20/stream -map 0 -map 1 -c copy -t 15 -y twovideotracks.ts ffmpeg version 3.0.1-static http://johnvansickle.com/ffmpeg/ Copyright (c) 2000-2016 the FFmpeg developers built with gcc 5.3.1 (Debian 5.3.1-13) 20160323 configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --enable-libmp3lame --enable-libx264 --enable-libx265 --enable-libwebp --enable-libspeex --enable-libvorbis --enable-libvpx --enable-libfreetype --enable-fontconfig --enable-libxvid --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvo-amrwbenc --enable-gray --enable-libopenjpeg --enable-libopus --enable-libass --enable-gnutls --enable-libvidstab --enable-libsoxr --enable-frei0r --enable-libfribidi --disable-indev=sndio --disable-outdev=sndio --enable-librtmp --enable-libmfx --enable-libzimg --cc=gcc libavutil 55. 17.103 / 55. 17.103 libavcodec 57. 24.102 / 57. 24.102 libavformat 57. 25.100 / 57. 25.100 libavdevice 57. 0.101 / 57. 0.101 libavfilter 6. 31.100 / 6. 31.100 libswscale 4. 0.100 / 4. 0.100 libswresample 2. 0.101 / 2. 0.101 libpostproc 54. 0.100 / 54. 0.100 Splitting the commandline. Reading option '-v' ... matched as option 'v' (set logging level) with argument 'debug'. Reading option '-thread_queue_size' ... matched as option 'thread_queue_size' (set the maximum number of queued packets from the demuxer) with argument '512'. Reading option '-rtsp_transport' ... matched as AVOption 'rtsp_transport' with argument 'tcp'. Reading option '-i' ... matched as input file with argument 'rtsp:// 192.168.1.20/stream'. Reading option '-thread_queue_size' ... matched as option 'thread_queue_size' (set the maximum number of queued packets from the demuxer) with argument '512'. Reading option '-rtsp_transport' ... matched as AVOption 'rtsp_transport' with argument 'tcp'. Reading option '-allowed_media_types' ... matched as AVOption 'allowed_media_types' with argument 'video'. Reading option '-i' ... matched as input file with argument 'rtsp:// 192.168.1.20/stream'. Reading option '-map' ... matched as option 'map' (set input stream mapping) with argument '0'. Reading option '-map' ... matched as option 'map' (set input stream mapping) with argument '1'. Reading option '-c' ... matched as option 'c' (codec name) with argument 'copy'. Reading option '-t' ... matched as option 't' (record or transcode "duration" seconds of audio/video) with argument '15'. Reading option '-y' ... matched as option 'y' (overwrite output files) with argument '1'. Reading option 'twovideotracks.ts' ... matched as output file. Finished splitting the commandline. Parsing a group of options: global . Applying option v (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://192.168.1.20/stream. Applying option thread_queue_size (set the maximum number of queued packets from the demuxer) with argument 512. Successfully parsed a group of options. Opening an input file: rtsp://192.168.1.20/stream. [tcp @ 0x4471480] No default whitelist set [rtsp @ 0x446f600] SDP: v=0 o=- -2670153692969325330 -2670153692968316012 IN IP4 192.168.1.20 c=IN IP4 0.0.0.0 a=tool: RtpRtspServer a=range:npt=0- m=audio 0 RTP/AVP 98 a=rtpmap:98 mpeg4-generic/48000/2 a=fmtp:98 streamtype=5; profile-level-id=15; mode=AAC-hbr; config=1190; SizeLength=13;IndexLength=3; IndexDeltaLength=3; Profile=1; a=control:rtsp://192.168.1.20:554/stream/trackID=0 m=video 0 RTP/AVP 96 a=rtpmap:96 H264/90000 a=fmtp:96 packetization-mode=1;profile-level-id=42001e;sprop-parameter-sets=Z2QAKK2wpDBSAgFxQWKQPQRWFIYKQEAuKCxSB6CKwpDBSAgFxQWKQPQRTDoUKQNC4oJHMGIemHQoUgaFxQSOYMQ9MOhQpA0LigkcwYh6xEQmIVilsQRWUURJsogxOU4QITKUIEVlCCTYQVhBMJQhMIjGggWQJFaIGBJZBAaEnaMIDwsSWQQKCwsrRBQYOWQweO0YEBZASNAogszlAeAIn5cBEAAAu4AAK/IOAAADA9CQAAA7msr//4wAAAehIAAAdzWV//8K,aP48sA==; a=control:rtsp://192.168.1.20:554/stream/trackID=1 Failed to parse interval end specification '' [rtsp @ 0x446f600] audio codec set to: aac [rtsp @ 0x446f600] audio samplerate set to: 48000 [rtsp @ 0x446f600] audio channels set to: 2 [rtsp @ 0x446f600] video codec set to: h264 [rtsp @ 0x446f600] RTP Packetization Mode: 1 [rtsp @ 0x446f600] RTP Profile IDC: 42 Profile IOP: 0 Level: 1e [rtsp @ 0x446f600] Extradata set to 0x4475930 (size: 210) [NULL @ 0x44723a0] setting jitter buffer size to 0 [NULL @ 0x4475280] setting jitter buffer size to 0 [rtsp @ 0x446f600] hello state=0 [h264 @ 0x4475280] Frame num gap 13 8 [h264 @ 0x4475280] Frame num gap 13 9 [h264 @ 0x4475280] Frame num gap 13 10 [h264 @ 0x4475280] Frame num gap 13 11 [rtsp @ 0x446f600] All info found Input #0, rtsp, from 'rtsp://192.168.1.20/stream': Duration: N/A, start: 0.000000, bitrate: N/A Stream #0:0, 46, 1/48000: Audio: aac (LC), 48000 Hz, stereo, fltp Stream #0:1, 29, 1/90000: Video: h264 (High), 4 reference frames, yuv420p(left), 1920x1080 (1920x1088) [SAR 1:1 DAR 16:9], 1/60, 30 fps, 30 tbr, 90k tbn, 60 tbc Successfully opened the file. Parsing a group of options: input file rtsp://192.168.1.20/stream. Applying option thread_queue_size (set the maximum number of queued packets from the demuxer) with argument 512. Successfully parsed a group of options. Opening an input file: rtsp://192.168.1.20/stream. [tcp @ 0x44a69c0] No default whitelist set [rtsp @ 0x44c04e0] SDP: v=0 o=- -2670153688428557055 -2670153688427642227 IN IP4 192.168.1.20 c=IN IP4 0.0.0.0 a=tool: RtpRtspServer a=range:npt=0- m=audio 0 RTP/AVP 98 a=rtpmap:98 mpeg4-generic/48000/2 a=fmtp:98 streamtype=5; profile-level-id=15; mode=AAC-hbr; config=1190; SizeLength=13;IndexLength=3; IndexDeltaLength=3; Profile=1; a=control:rtsp://192.168.1.20:554/stream/trackID=0 m=video 0 RTP/AVP 96 a=rtpmap:96 H264/90000 a=fmtp:96 packetization-mode=1;profile-level-id=42001e;sprop-parameter-sets=Z2QAKK2wpDBSAgFxQWKQPQRWFIYKQEAuKCxSB6CKwpDBSAgFxQWKQPQRTDoUKQNC4oJHMGIemHQoUgaFxQSOYMQ9MOhQpA0LigkcwYh6xEQmIVilsQRWUURJsogxOU4QITKUIEVlCCTYQVhBMJQhMIjGggWQJFaIGBJZBAaEnaMIDwsSWQQKCwsrRBQYOWQweO0YEBZASNAogszlAeAIn5cBEAAAu4AAK/IOAAADA9CQAAA7msr//4wAAAehIAAAdzWV//8K,aP48sA==; a=control:rtsp://192.168.1.20:554/stream/trackID=1 Failed to parse interval end specification '' [rtsp @ 0x44c04e0] video codec set to: h264 [rtsp @ 0x44c04e0] RTP Packetization Mode: 1 [rtsp @ 0x44c04e0] RTP Profile IDC: 42 Profile IOP: 0 Level: 1e [rtsp @ 0x44c04e0] Extradata set to 0x45e6df0 (size: 210) [NULL @ 0x44c0e40] setting jitter buffer size to 0 [rtsp @ 0x44c04e0] hello state=0 [rtsp @ 0x44c04e0] All info found Input #1, rtsp, from 'rtsp://192.168.1.20/stream': Duration: N/A, start: 0.200000, bitrate: N/A Stream #1:0, 28, 1/90000: Video: h264 (High), 4 reference frames, yuv420p(left), 1920x1080 (1920x1088) [SAR 1:1 DAR 16:9], 1/60, 30 fps, 30 tbr, 90k tbn, 60 tbc Successfully opened the file. Parsing a group of options: output file twovideotracks.ts. Applying option map (set input stream mapping) with argument 0. Applying option map (set input stream mapping) with argument 1. Applying option c (codec name) with argument copy. Applying option t (record or transcode "duration" seconds of audio/video) with argument 15. Successfully parsed a group of options. Opening an output file: twovideotracks.ts. [file @ 0x45e6f20] Setting default whitelist 'file,crypto' Successfully opened the file. [mpegts @ 0x44be9c0] muxrate VBR, pcr every 9000 pkts, sdt every 200, pat/pmt every 40 pkts Output #0, mpegts, to 'twovideotracks.ts': Metadata: encoder : Lavf57.25.100 Stream #0:0, 0, 1/90000: Audio: aac (LC), 48000 Hz, stereo Stream #0:1, 0, 1/90000: Video: h264, 1 reference frame, yuv420p(left), 1920x1080 (0x0) [SAR 1:1 DAR 16:9], 1/90000, q=2-31, 30 fps, 30 tbr, 90k tbn, 90k tbc Stream #0:2, 0, 1/90000: Video: h264, 1 reference frame, yuv420p(left), 1920x1080 (0x0) [SAR 1:1 DAR 16:9], 1/90000, q=2-31, 30 fps, 30 tbr, 90k tbn, 90k tbc Stream mapping: Stream #0:0 -> #0:0 (copy) Stream #0:1 -> #0:1 (copy) Stream #1:0 -> #0:2 (copy) Press [q] to stop, [?] for help cur_dts is invalid (this is harmless if it occurs once at the start per stream) Last message repeated 13 times [mpegts @ 0x44be9c0] Non-monotonous DTS in output stream 0:2; previous: 0, current: -15000; changing to 1. This may result in incorrect timestamps in the output file. [mpegts @ 0x44be9c0] Non-monotonous DTS in output stream 0:2; previous: 1, current: -12000; changing to 2. This may result in incorrect timestamps in the output file. [mpegts @ 0x44be9c0] Non-monotonous DTS in output stream 0:2; previous: 2, current: -9000; changing to 3. This may result in incorrect timestamps in the output file. [mpegts @ 0x44be9c0] Non-monotonous DTS in output stream 0:2; previous: 3, current: -6000; changing to 4. This may result in incorrect timestamps in the output file. [mpegts @ 0x44be9c0] Non-monotonous DTS in output stream 0:2; previous: 4, current: -3000; changing to 5. This may result in incorrect timestamps in the output file. [mpegts @ 0x44be9c0] Non-monotonous DTS in output stream 0:2; previous: 5, current: 0; changing to 6. This may result in incorrect timestamps in the output file. No more output streams to write to, finishing.4kB time=00:00:14.93 bitrate=4500.7kbits/s speed=1.05x frame= 449 fps= 31 q=-1.0 Lq=-1.0 size= 8240kB time=00:00:15.01 bitrate=4494.6kbits/s speed=1.05x video:7350kB audio:180kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 9.434474% Input file #0 (rtsp://192.168.1.20/stream): Input stream #0:0 (audio): 705 packets read (184612 bytes); Input stream #0:1 (video): 451 packets read (3718936 bytes); Total: 1156 packets (3903548 bytes) demuxed Input file #1 (rtsp://192.168.1.20/stream): Input stream #1:0 (video): 457 packets read (3824077 bytes); Total: 457 packets (3824077 bytes) demuxed Output file #0 (twovideotracks.ts): Output stream #0:0 (audio): 704 packets muxed (184384 bytes); Output stream #0:1 (video): 449 packets muxed (3709109 bytes); Output stream #0:2 (video): 456 packets muxed (3816889 bytes); Total: 1609 packets (7710382 bytes) muxed 0 frames successfully decoded, 0 decoding errors [AVIOContext @ 0x45ecaa0] Statistics: 0 seeks, 1027 writeouts