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• video processing on android using ndk with ffmpeg and opencv is very slow

  26 novembre 2014, par Zhiqiang Li

  I’m doing some video processing on android using ndk.

  What I’m doing now is decode the video using ffmpeg, grab the frame, convert it to opencv mat, then overlay some images on it, then convert it back to avframe, encode it back to a video.

  But it’s very slow ! It takes about 50 seconds to process a 480*480 video with 15 fps.

  I tried to do this using opengl es, reading the result image using glReadPixels, but from what I understand, glReadPixels doesn’t really work on some devices. So I had to give it up.

  As I understand, I have some very expensive operations in my current workflow,

  1. covert a AVFrame from yuv to bgr color space, then convert to opencv mat
  2. overlay a mat on another mat
  3. covert a opencv mat to AVFrame, then convert the frame from bgr to yuv space, then encode it into a video.

  So, are there ways to improve my current workflow ?

  I’m adding multithread feature, but only devices with multicore cup can benefit from that.

• How to effectively kill a frozen subprocess in Python ?

  2 janvier 2014, par Konos5

  I am dealing with a rather odd issue.

  I've written a Python wrapper (in Python 2.6.6) for a year old version of ffmpeg. The problem is that given a very particular video, ffmpeg stops working normally (clunky output, full cpu usage, no end stage etc) and takes the python interpreter down with it.

  Now, if I run ffmpeg with my encoding options directly from a terminal and the problematic video as input, ffmpeg won't immediately respond to Ctrl-c. I'll have to wait for a hefty of 10 seconds or more before it exits and gives me back the prompt. However if I use a 'healthy' video instead, it will simply print Received signal 2: terminating. and gracefully exit.

  In the python wrapper I use p.kill() to no effect. The behavior is exactly the same a.k.a I have to wait 10 sec before the program exits. How can I immediately stop ffmpeg when it freezes with some problematic video ?

  Note that if I do a double Ctrl-c I get the prompt back immediately no matter what.

• Create mp4 file from raw h264 using a pipe instead of files

  16 avril 2019, par Charlie Burns

  I have a raw h264 file that I can display with VLC, on a mac :

  open -a VLC file.h264

  I can convert this to mp4 with the command line

  ffmpeg -f h264 -i file.h264 -c:v copy file.mp4

  But what I really want to do is something like :

  cat file.h264 | ffmpeg > file.mp4

  Reason being that the input is coming over a socket and I want to convert it and send it to a video tag in an html file on the fly.

  An alternative solution would be a way to display the raw h264 in a web page without converting it to mp4 first.

  The input is coming in frame by frame, the first four bytes are 0,0,0,1. My understanding is that this h264 Annex B format.

  I know nothing about video formats, I would grateful to be pointed in a direction to look.

  Should I look into writing code using libavcodec like this quuesion or is there an off-the-shelf solution ?

  H.264 muxed to MP4 using libavformat not playing back

  Thanks !