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• ffmpeg and Red5 Issue : Increase in number of ffmpeg simultaneous streams to Red5 resulting in packet loss

  30 octobre 2014, par kajarigd

  I have a screen sharing app written in flex, using which one person can share his screen with another person via Red5 server (Version : 1.0.3). Platform is Windows Server 2008. Now, I want to load test this Red 5 server to find out maximum how many simultaneous screen sharing session it can allow, without any quality compromise. By quality I mean, speed of transmission and no data loss during transmission. I simulated the load using ffmpeg command.

  For this, instead of transmitting a live captured screen, I am transmitting (uploading) a FLV file stored in my local to the Red5 server using ffmpeg command. In the receiving client side, I am starting to download (transmitting) this same FLV file after 5 secs since the upload has started. This is working fine when I am running this test for less than 10 pairs of upstreaming-downstreaming sessions. But, when the number is increasing beyond 10, I am observing significant packet loss in transmission.

  Here are the commands I am running in a loop. The loop count is the number of streaming pairs.

  1. upstreaming : ffmpeg -re -i  -f flv -ar 22050 "rtmp://" -report
  2. downstreaming : ffmpeg -re -i "rtmp:// live=1"  -report

  The and are set in such a way, that in the downstream I will download the same uploaded file. "rtmp ://" are the same in both the cases. I am not doing the upstream in record mode, hence, no physical file is getting saved in the server side. When I am analyzing the file I received in the receiving client side, it is a poor quality video due to frame loss. Uploading and downloading machines are two different machines. I ran the test for many hours, repeating the same 10 simultaneous streaming sets. Each set is consistently giving the same results.

  What is puzzling me is, this is working fine without any packet loss for less that 10 simultaneous streaming. I searched about it in various forums, but none of the answers were applicable for this scenario. For a while I was thinking that Red5 has limited capacity, but I found many posts saying Red5 can easily scale up to take very big load. Does that mean, the problem is in my configuration ? I am not sure which are to focus on.

  An example log snippet :

  Lots of missing data at downstream side. For e.g. between frames 101 and 102 there is a difference of 25 sec. On replaying the video there is a stoppage for this much time.In this time gap all the frames are lost.

  frame=  101 fps=1.0 q=14.5 size=    2650kB time=00:01:41.00 bitrate= 214.9kbits/s
  
  frame=  102 fps=1.0 q=13.2 size=    2763kB time=00:02:06.00 bitrate= 179.6kbits/s

  Any help is appreciated !

• How to find the presentation time stamp of a given frame number for FFMPEG decoding ?

  21 août 2017, par Deepankar Arya

  I am using the C APIs of ffmpeg for some video processing. My aim is to extract the screen shot of a given frame number. I have understood that ffmpeg has an av_seek_frame function to seek to a given timestamp(expressed in appropriated base units of the video stream). I assume that I will have to goto to the most recent I frame for the given frame(using the AVSEEK_FLAG_BACKWARD flag) and read onwards untill I meet the required frame. For that I need to give a seek time stamp to the av_seek_frame function. My main issue is that given a frame number, how do I find an associated presentation time stamp to seek to ?

• rtmpproto : Add function to read a number response

  14 octobre 2014, par Uwe L. Korn

  rtmpproto : Add function to read a number response
  Packets that contain a number as a result to a rtmp function call are
  
  structured the same way (String, Number, Null, Number). This new method
  
  also includes more bounds checks to better handle packets that are not
  
  structured as expected.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavformat/rtmpproto.c