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• FFMPEG : Recurring onMetaData for RTMP ? [on hold]

  30 novembre 2017, par stevendesu

  For whatever reason this was put on hold as "too broad", although I felt I was quite specific. So I’ll try rephrasing here :

  My former understanding :

  The RTMP Protocol involves sending several parallel streams of data as a series of packets, with an ID correlating to which stream they are a part of. For instance :

  [VIDEO] <data>
  
  [AUDIO] <data>
  
  [VIDEO] <data>
  
  [VIDEO] <data>
  
  [SERVER] <metadata about="about" bandwidth="bandwidth">
  
  [VIDEO] <data>
  
  [AUDIO] <data>
  
  ...
  
  </data></data></metadata></data></data></data></data>

  Then on the player side these packets are split up into separate buffers based on type (all video data is concatenated, all audio data is concatenated, etc)

  One of the packet types is called onMetaData (ID : 0x12)

  An onMetaData packet includes a timestamp for when to trigger the metadata (this way it can be synchronized with the video) as well as the contents of the metadata (a text string)

  My setup :

  I’m using Red5Pro as my ingest server to take in an RTMP stream and then watch this stream via WebRTC. When an onMetaData packet is received by Red5, it sends out a JSON object to all subscribers of the stream over WebSockets with the contents of the stream.

  What I want :

  I want to take advantage of this onMetaData channel to embed the server’s system clock into a stream. This way anyone viewing the stream can determine when (according to the server) a stream was encoded and, if they synchronize their clock with the server, they can then compute the end-to-end latency of the stream. Due to Red5’s use of WebSockets to send metadata this isn’t a perfect solution (you may receive the metadata before or after you actually receive the video information), however I have some plans to work around this.

  In other words, I want my stream to look like this :

  [VIDEO] <data>
  
  [AUDIO] <data>
  
  [ONMETADATA] time: 2:05:77.382
  
  [VIDEO] <data>
  
  [VIDEO] <data>
  
  [SERVER] <metadata about="about" bandwidth="bandwidth">
  
  [VIDEO] <data>
  
  [ONMETADATA] time: 2:05:77.423
  
  [AUDIO] <data>
  
  ...
  
  </data></data></metadata></data></data></data></data>

  What I would like is to generate this stream (with the server’s current time periodically embedded into the onMetaData channel) using FFMPEG

  Simpler problem :

  FFMPEG offers a -metadata command-line parameter.

  In my experiments, using this parameter caused a single onMetaData event to be fired including things like "title", "author", etc. I could not inject additional onMetaData packets periodically as the stream progressed.

  Even if the metadata packets do not contain the system clock, if I could send any metadata packets periodically using FFMPEG then I could include something static like "the server’s clock at the time the broadcast started". I can then compare this to the current timestamp of the video and calculate the latency.

  My confusion :

  Continuing to look into this after creating my post, there are a couple things that I don’t fully understand or which don’t quite make sense to me. For one, if FFMPEG is only injecting a single onMetaData packet into the stream, then I would expect anyone joining the stream late to miss it. However when I join the stream 8 hours later I see Red5 send me the metadata packet complete with title, author, etc. So it’s almost like the metadata packet doesn’t have a timestamp associated with it but instead is just generic metadata about the video

  Furthermore, there’s something called "AMF" which I’m not familiar with, but it may be important ?

  Original Post

  I spent today playing around with methods to embed the system clock at time of encode into a stream, so that I could compare this value to the same system clock at time of decode to get a rough estimate of RTMP latency. Unfortunately the majority of techniques I used ended up failing.

  One thing I wanted to try next was taking advantage of RTMP’s onMetaData to send the current system clock periodically (maybe every 5 seconds) as part of the stream for any clients to listen for.

  Unfortunately FFMPEG’s -metadata option seems to only be for one-time metadata when the stream first loads. I can’t figure out how to add continuous (and generated) values to a stream.

  Is there a way to do this ?

• Unable to get current time in TCL. can i use flush here ?

  30 novembre 2017, par M. D. P

  unable to get current time for the bellow code :

  proc a {} { 
  
  
  
          for {set i 0} {$i < 3} {incr i} {
  
      puts " $i "
  
  
  
  
  
                  set imagetime [clock format [clock seconds] -format %Y%m%d_%H%M%S]
  
                  set videotime [clock format [clock seconds] -format %Y%m%d_%H%M%S]
  
       
  
                  exec ffmpeg -f dshow -i "video=Integrated Webcam" -s 1280x720 -benchmark c:/test/Image_$imagetime.jpg >& c:/test/image_$imagetime.txt &
  
  
  
                  after 15000
  
  
  
                  exec ffmpeg -f dshow -t 00:00:10 -i "video=Integrated Webcam" -s 1280x720 -benchmark c:/test/video_$videotime.avi >& c:/test/video_$videotime.txt &
  
                  
  
                  after 15000
  
          } 
  
  }
  
  a

  the output is :

  

  the problem here is, even though the variable for taking video time and image time is different, it is tacking same time for video and image.

  any reason or solution for this ????

  can i use flush command ???

  can i work with following code :

  proc a {} { 
  
  
  
          for {set i 0} {$i < 3} {incr i} {
  
      puts " $i "
  
  
  
  set time [clock format [clock seconds] -format %Y%m%d_%H%M%S]
  
                       
  
                  exec ffmpeg -f dshow -i "video=Integrated Webcam" -s 1280x720 -benchmark c:/test/Image_$time.jpg >& c:/test/image_$time.txt &
  
  
  
                  after 15000
  
  
  
                  exec ffmpeg -f dshow -t 00:00:10 -i "video=Integrated Webcam" -s 1280x720 -benchmark c:/test/video_$time.avi >& c:/test/video_$time.txt &
  
                  
  
                  after 15000
  
          } 
  
  }
  
  a

  any answer ??

• FFMPEG : embed current time in milliseconds into video [closed]

  5 juin, par stevendesu

  I would like to embed the computer's local time in milliseconds into a stream using FFMPEG.

  



  I can embed the local time in seconds using drawtext like so :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{localtime\:%T}&#x27;" -f flv <output>&#xA;</output>

  



  Looking through the documentation for drawtext, doing some tests, and Googling around, it seems like localtime and gmtime don't provide milliseconds — just seconds. However the pts options does have milliseconds :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{pts\:hms}&#x27;" -f flv <output>&#xA;</output>

  



  I also found out that pts supports an offset, so I was able to use something like this to display local time (kind of) :

  



  ffmpeg -i <input /> -vf "drawtext=text=&#x27;%{pts\:hms\:$(date &#x2B;%s.%N)}&#x27;" -f flv <output>&#xA;</output>

  



  This had two problems :

  



  

  1. It displayed something like 17499:17:29 for the time... I found a (rather complex) way to work around this

  


  2. It uses the server's current time when you first run the ffmpeg command as the offset — not the server's current time when ffmpeg actually starts decoding video. I noticed ffmpeg had about a 2-second startup time, causing the clock to be off by roughly 2 seconds

  


  



  Is there a way to modify my solution, or an entirely separate solution, that can embed server local time in milliseconds into the stream ?