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• Flush & Latency Issue with Fragmented MP4 Creation in FFMPEG

  1er août 2023, par galbarm

  I'm creating a fragmented mp4 for html5 streaming, using the following command :

  



  -i rtsp://172.20.28.52:554/h264 -vcodec copy -an -f mp4 -reset_timestamps 1 -movflags empty_moov+default_base_moof+frag_keyframe -loglevel quiet -


  



  

  1. "-i rtsp ://172.20.28.52:554/h264" because the source is h264 in rtp packets stream from an ip camera.
For the sake of testing, the camera is set with GOP of 1 (i.e. all frames are key frames)

  


  2. "-vcodec copy" because I don't need transcoding, only remuxing to mp4.

  


  3. "-movflags empty_moov+default_base_moof+frag_keyframe" to create a fragmented mp4 according to the media source extensions spec.

  


  4. "-" at the end in order to output the mp4 to stdout. I'm grabbing the ouput and sending it to the webclient through web sockets.

  


  



  Everything is working well, expect for a latency issue which I'm trying to solve.
If I'm logging every time a data is coming in from stdout, with the timestamp of arrival, I get this output :

  



  


  16/06/2015 15:40:45.239 got data size = 24

  
 


  16/06/2015 15:40:45.240 got data size = 7197

  
 


  16/06/2015 15:40:45.241 got data size = 32768

  
 


  16/06/2015 15:40:45.241 got data size = 4941

  
 


  16/06/2015 15:40:45.241 got data size = 12606

  
 


  16/06/2015 15:40:45.241 got data size = 6345

  
 


  16/06/2015 15:40:45.241 got data size = 6339

  
 


  16/06/2015 15:40:45.242 got data size = 6336

  
 


  16/06/2015 15:40:45.242 got data size = 6361

  
 


  16/06/2015 15:40:45.242 got data size = 6337

  
 


  16/06/2015 15:40:45.242 got data size = 6331

  
 


  16/06/2015 15:40:45.242 got data size = 6359

  
 


  16/06/2015 15:40:45.243 got data size = 6346

  
 


  16/06/2015 15:40:45.243 got data size = 6336

  
 


  16/06/2015 15:40:45.243 got data size = 6338

  
 


  16/06/2015 15:40:45.243 got data size = 6357

  
 


  16/06/2015 15:40:45.243 got data size = 6357

  
 


  16/06/2015 15:40:45.243 got data size = 6322

  
 


  16/06/2015 15:40:45.243 got data size = 6359

  
 


  16/06/2015 15:40:45.244 got data size = 6349

  
 


  16/06/2015 15:40:45.244 got data size = 6353

  
 


  16/06/2015 15:40:45.244 got data size = 6382

  
 


  16/06/2015 15:40:45.244 got data size = 6403

  
 


  16/06/2015 15:40:45.304 got data size = 6393

  
 


  16/06/2015 15:40:45.371 got data size = 6372

  
 


  16/06/2015 15:40:45.437 got data size = 6345

  
 


  16/06/2015 15:40:45.504 got data size = 6352

  
 


  16/06/2015 15:40:45.571 got data size = 6340

  
 


  16/06/2015 15:40:45.637 got data size = 6331

  
 


  16/06/2015 15:40:45.704 got data size = 6326

  
 


  16/06/2015 15:40:45.771 got data size = 6360

  
 


  16/06/2015 15:40:45.838 got data size = 6294

  
 


  16/06/2015 15:40:45.904 got data size = 6328

  
 


  16/06/2015 15:40:45.971 got data size = 6326

  
 


  16/06/2015 15:40:46.038 got data size = 6326

  
 


  16/06/2015 15:40:46.105 got data size = 6340

  
 


  16/06/2015 15:40:46.171 got data size = 6341

  
 


  16/06/2015 15:40:46.238 got data size = 6332

  


  



  As you can see, the first 23 lines (which contain data of about 1.5 secs of video) are arriving almost instantly, and then the delay between each 2 consecutive lines is 70ms which makes sense because the video is 15 frames per sec.
This behavior introduces a latency of about 1.5 sec.

  



  It looks like a flushing issue because I don't see any reason why would ffmpeg need to hold the first 23 frames in memory, especially since each frame is a fragment of it's own inside the mp4.
I couldn't however, find any method that would cause ffmpeg to flush this data faster.

  



  Has anyone got a suggestion ?

  



  I'd like to note that this is a follow up question to this one :
Live streaming dash content using mp4box

  


• ffmpeg rtsp stream is fragmenting - what is the optimal bitrate/other options ? [closed]

  20 avril 2023, par unsaltedbutter97

  I am attempting to run 12 streams with ffmpeg, using this script :

  


  #!/bin/bash

ffmpeg -re -stream_loop -1 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-i test.mp4 \
-map 0 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream0 \
-map 1 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream1 \
-map 2 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream2 \
-map 3 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream3 \
-map 4 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream4 \
-map 5 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream5 \
-map 6 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream6 \
-map 7 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream7 \
-map 8 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream8 \
-map 9 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream9 \
-map 10 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream10 \
-map 11 -c: libx264 -b:v 500k -f rtsp rtsp://localhost:8554/mystream11


  


  I don't really understand the -b:v option. Video resolution is 3072x1728, 10 FPS,with an online tool I calculated that each stream requires 3.4 Mbps bitrate. But the more I increase the -b:v option, for example, to 3400k, the more fragmentation I get. My assumption would be that my network cannot keep up with encoding 3.4 Mbps of data, although I use wired 1000 Mb/s.

  


  Which options should I use to run streams without fragmentation ?

  


  I tried changing the -b:v parameter to multiple values. 100k was not enough, stream was simply stuck. 500k there is a little bit of fragmentation, same with 1000k. With 3400k the whole stream is fragmented.

  


• Building ffmpeg libraries for third party usage

  23 mars 2023, par mikeProgrammer

  I am trying to create bindings for FFmpeg in Elixir programming language and would love to handle FFmpeg binaries for users of my library.

  


  The whole flow is as follows :

  


  

  1. Write some function definition in Elixir

  


  2. Implement it in in C using ffmpeg libs

  


  3. Compile C code as shared library

  


  4. When running application, Erlang Virtual Machine will load my dynamic library

  


  


  The question is how to compile and include ffmpeg libs in my shared lib so that users of my Elixir lib don't have to install any native dependencies.

  


  Here is what I was trying :

  


  


  1. Compile ffmpeg libs as shared ones. When my Elixir lib is compiling, it downloads precompiled ffmpeg archive, extracts its content and links to it when compiling native functions. I realized that this still won't work as ffmpeg shared libs depend on other shared libs that user has to install on their own.

     


  


  2. Compile ffmpeg libs as static ones and include them in my native shared library using —whole-archive linker option. Here I am getting

     


  


  


  /usr/bin/ld : ffmpeg_build/lib/libavcodec.a(vp9lpf_16bpp.o) : warning : relocation against ff_pw_1' in read-only section .text'
/usr/bin/ld : ffmpeg_build/lib/libavcodec.a(cavsdsp.o) : relocation R_X86_64_PC32 against symbol `ff_pw_5' can not be used when making a shared object ; recompile with -fPIC
/usr/bin/ld : final link failed : bad value
collect2 : error : ld returned 1 exit status

  


  The command I am using

  


  cc -fPIC -I/home/michal/.asdf/installs/erlang/25.1/erts-13.1/include -Iffmpeg_build/include -Ic_src/xav -shared -DXAV_DEBUG=1 c_src/xav/xav_nif.c c_src/xav/reader.c c_src/xav/utils.c -o /home/michal/Repos/xav/_build/test/lib/xav/priv/libxav.so -Lffmpeg_build/lib -Wl,--whole-archive -lavcodec -lswscale -lavutil -lavformat -Wl,--no-whole-archive


  


  FFmpeg configuration

  


  ./configure \
--prefix="$PWD/ffmpeg_build" \
--extra-cflags="-fPIC -I$PWD/ffmpeg_build/include" \
--extra-ldflags="-L$PWD/ffmpeg_build/lib" \
--enable-pic
--disable-programs


  


  Does anything that I am trying to do make sense to you ?

  


  When I am installing ffmpeg-libs package on Fedora, it depends on other shared libs that are automatically downlaoded but what I would love to achieve is to provide self-contained ffmpeg build that can be used in other shared libraries.