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• Forcing custom H.264 intra-frames (keyframes) at encode-time ?

  1er juin 2017, par Henry Cooke

  I have a video sequence that I’d like to skip to specific frames at playback-time (my player is implemented using AVPlayer in iOS, but that’s incidental). Since these frames will fall at unpredictable intervals, I can’t use the standard "keyframe every N frames/seconds" functionality present in most video encoders. I do, however, know the target frames in advance.

  In order to do this skipping as efficiently as possible, I need to force the target frames to be i-frames at encode time. Ideally in some kind of GUI which would let me scrub to a frame, mark it as a keyframe, and then (re)encode my video.

  If such a tool isn’t available, I have the feeling this could probably be done by rolling a custom encoder with libavcodec, but I’d rather use a higher-level (and preferably scriptable) tool to do the job if a GUI isn’t possible. Is this the kind of task ffmpeg or mencoder can be bent to ?

  Does anybody have a technique for doing this ? Also, it’s entirely possible that this is an impossible task because of some fundamental ignorance I have of the h.264 codec. If so, please do put me right.

• live streamming using ffmpeg for more than stream on the same time

  29 novembre 2016, par بسمة أمل

  I’m using this command to stream video in ffmpeg but when I stream more than 3 or 4 streams at the same time interruption happen although the process in my device doesn’t exceed 50%
  I tried to use ffmpeg lib for each stream but interruption still happened

  this is my command :

   ffmpeg -re -i test.mp4 -i logo.png -vcodec libx264 -pix_fmt yuv420p -vb 2000000 -g 60 
  
  -vprofile main -acodec aac -ab 128000 -ar 48000 -ac 2 -vbsf h264_mp4toannexb 
  
  -strict experimental -filter_complex "[0][1]overlay=0:0" 
  
  -pass 1 -f mpegts udp://127.0.0.1:1234?pkt_size=1316

• 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 ?