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• mmaldec : fix problems with flush logic

  11 août 2015, par wm4

  mmaldec : fix problems with flush logic
  Don’t try to do a blocking wait for MMAL output if we haven’t even sent
  
  a single real packet, but only flush packets. Obviously we can’t expect
  
  to get anything back.
  Additionally, don’t send a flush packet to MMAL in the same case. It
  
  appears the MMAL decoder will sometimes hang in mmal_vc_port_disable()
  
  (called from ffmmal_close_decoder()), waiting for a reply from the GPU
  
  which never arrives. Either MMAL disallows sending flush packets without
  
  preceding real data, or it’s a MMAL bug.
  

  • [DH] libavcodec/mmaldec.c

• How to run ffmpeg as c program

  12 mars 2015, par Yonghao Zhao

  I am a student currently work on real-time video transmission, recently I found ffmpeg command line is very powerful in real-time encoding/decoding.

  But what I want to do is move the c program of the encoding/decoding part (corresponding to ffmpeg command line) into our general big c program.

  The problem is, I have already found the corresponding c program file in ffmpeg source folder (but actually I am not sure whether it is or not) its in home/ffmpeg sources/ffmpeg/example/decoding_encoding.c.

  I opened the file but cannot run it in Codeblocks, it gives the error

  undefined reference to 'av_crc'

  and a lot of ’undefined reference’ error.

  1. Does anybody have any idea how to solve this ?
  2. And any other idea of how to trans ffmepg command line to c program ?

• very low latency streaminig with ffmpeg using a webcam

  22 mars 2017, par userDtrm

  I’m trying to configure ffmpeg to do a real-time video streaming using a webcam. The ffmpeg encoder command I use is as follows.

  ffmpeg -f v4l2 -input_format yuyv422 -s 640x480 -i /dev/video0 -c:v libx264 -profile:v baseline -trellis 0 -subq 1 -level 32 -preset superfast -tune zerolatency -me_method epzs -crf 30 -threads 0 -bufsize 1 -refs 4 -coder 0 -b_strategy 0 -bf 0 -sc_threshold 0 -x264-params vbv-maxrate=2000:slice-max-size=1500:keyint=30:min-keyint=10: -pix_fmt yuv420p -an -f mpegts udp://192.168.1.8:5001

  The ffplay command used to display the video feed is,

  ffplay -analyzeduration 1 -fflags -nobuffer -i udp://192.168.1.8:5001

  However, I’m experiencing a latency of 0.5 - 1.0s latency in the video stream. Is there a way to reduce this to a number less than 100ms. Also, when I replace the v4l2 camera capture with a screen capture using x11grab, the stream is almost real-time and I experience no noticeable delays. Moreover, changing the encoder from x264 to mpeg2 had no effect on the latency. In addition, the statistics from the ffmpeg shows that the encoder is performing at a 30fps rate, which I believe indicates that the encoding is real-time. This leaves me with only one reason for the experienced delay.

  • Is there a significant delay in buffers when using v4l2 during video capturing in a webcam ?
  • I don’t think the transmission delay is in effect in this case as I see no latencies when screen capture is used under the same conditions.
  • Can this latency be further reduced ?. Can someone think of a different encoder configuration to be used instead of the one that I’ve been using ?.

  Any suggestions or assistance is highly appreciated.

  Thank You.