[FFmpeg-user] Synchronizing RTSP signals with FFMPEG

[Miguel Titos]

Hi,

I have achieved to merge two RTSP signals in one with FFMPEG but in the
resulting stream, the first input has a delay of between 2 and 5 seconds
with respect to the second. And it is always the first input that is
delayed compared to the second.

The two RTSP signals come from the same camera model, same configuration,
same room ...

However, if I put the same RTSP signal (either of the two) as input 1 and
input 2, the same thing happens. Despite being the same signal, the first
input is delayed compared to the second one.

How could I get them synchronized?

This is the command that I execute:

ffmpeg -rtsp_transport tcp -thread_queue_size 512 -rtbufsize 50M -r 15
-i rtsp://XXXX -rtsp_transport tcp -thread_queue_size 512 -rtbufsize 50M -r
15
-c:a aac -i rtsp://XXXX -filter_complex
"[0:v]pad=iw*2:ih,setpts=PTS-STARTPTS[bg];
[1:v]setpts=PTS-STARTPTS[fg]; [bg][fg]overlay=w[out]" -map "[out]" -f hls
-hls_time 2 -hls_list_size 5 -use_localtime 1 -use_localtime_mkdir 1
-hls_segment_filename 'LIVE/file-%s.ts' -map a -ar 16000 -ac 1 -ab 64000
-c:a aac
-y output.m3u8

Here you have the process information:

ffmpeg version 3.4.2 Copyright (c) 2000-2018 the FFmpeg developers
built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
configuration: --prefix=/usr/local/Cellar/ffmpeg/3.4.2 --enable-shared
--enable-pthreads --enable-version3 --enable-hardcoded-tables
--enable-avresample --cc=clang --host-cflags= --host-ldflags=
--disable-jack --enable-gpl --enable-libmp3lame --enable-libx264
--enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
[rtsp @ 0x7fe284000e00] Missing PPS in sprop-parameter-sets, ignoring
Input #0, rtsp, from 'rtsp://XXXX':
  Metadata:
    title           : Media Presentation
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: h264 (Main), yuv420p(progressive), 1280x720, 15
fps, 15 tbr, 90k tbn, 30 tbc
    Stream #0:1: Audio: aac (LC), 16000 Hz, mono, fltp
[rtsp @ 0x7fe28484de00] Missing PPS in sprop-parameter-sets, ignoring
Input #1, rtsp, from 'rtsp://XXXX':
  Metadata:
    title           : Media Presentation
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #1:0: Video: h264 (Main), yuv420p(progressive), 1280x720, 15
fps, 15 tbr, 90k tbn, 30 tbc
    Stream #1:1: Audio: aac (LC), 16000 Hz, mono, fltp
Stream mapping:
  Stream #0:0 (h264) -> pad (graph 0)
  Stream #1:0 (h264) -> setpts (graph 0)
  overlay (graph 0) -> Stream #0:0 (libx264)
  Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x7fe286802000] using cpu capabilities: MMX2 SSE2Fast SSSE3
SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x7fe286802000] profile High, level 4.0
[libx264 @ 0x7fe286802000] 264 - core 152 r2854 e9a5903 - H.264/MPEG-4 AVC
codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options:
cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1
psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1
cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=12
lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0
bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1
b_bias=0 direct=1 weightb=1 open_gop=1 weightp=2 keyint=250 keyint_min=15
scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0
qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
[hls @ 0x7fe286800000] Opening 'LIVE/file-1524728763.ts' for writing
Output #0, hls, to 'output.m3u8'

Thanks in advance,
Miguel