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• Read h.264 video frames with opencv in python Enthough (mac Yosemite)

  3 février 2015, par Bertrand

  I’m using the Enthought distribution (Canopy) to do some data analysis and computer vision in the IPython notebook. I want to read the frames of several .avi files that use the h.264 codec and make some annotations on those images.

  if you’re using the Canopy distribution, you know that you can install opencv through the package manager (just launch the Canopy application, click on package manager, search for opencv and install the package). The issue though is that the following code

  import cv2
  
  f = "/Volumes/DATA/temp.avi"
  
  cap = cv2.VideoCapture(f)
  
  
  
  flag,frame = cap.read()
  
  
  
  print flag,frame

  always returns (None,None) because opencv can’t read the video. So it seems like ffmpeg is not enabled by default in the Enthought package manager.

  I’ve been losing a lot of time on this problem, so I’ll post the solution below. Hopefully it will help some other folks out there !

• Source of random Fatal signal 11 (SIGSEGV) error in app using ffmpeg through ndk

  20 janvier 2015, par grzebyk

  I am getting a nasty but well known error while working with FFmpeg and NDK :

  A/libc(9845): Fatal signal 11 (SIGSEGV), code 1, fault addr 0xa0a9f000 in tid 9921 (AsyncTask #4)

  What am I doing ?

  I am developing an application that streams live video feed from a webcam and enables user to pan and tilt the remote camera. I am using FFmpeg library built with NDK to achieve smooth playback with little delay.

  I am using FFMpeg library to connect to the video stream. Then the ndk part creates bitmap, does the image processing and render frames on the SurfaceView videoSurfaceView object which is located in the android activity (java part).

  To move the webcam I created a separate class - public class CameraMover implements Runnable{/**/}. This class is a separate thread that connects through sockets with the remote camera and manages tasks connected ONLY with pan-tilt movement.

  Next in the main activity i created a touch listener

  videoSurfaceView.setOnTouchListener(new View.OnTouchListener() {/**/
  
  cameraMover.setPanTilt(some parameters);
  
  /**/}

  which reads user’s finger movement and sends commands to the camera.

  All tasks - moving camera around, touch interface and video playback are working perfectly when the one of the others is disabled, i.e. when I disable possibility to move camera, I can watch video streaming and register touch events till the end of time (or battery at least). The problem occurs only when task are configured to work simultaneously.

  I am unable to find steps to reproduce the problem. It just happens, but only after user touches the screen to move camera. It can be 15 seconds after first interaction, but sometimes it takes app 10 or more minutes to crash. Usually it is something around a minute.

  What have I done to fix it ?

  • I tried to display millions of logs in logcat to find an error but
    the last log was always different.
  • I created a transparent surface, that I put over the videoSurfaceView and assigned touch listener to it. It all ended in the same error.
  • As I mentioned before, I turned off some functionalities to find which one produces the error, but it appears that error occurs only when everything is working simultaneously.

  Types of the error

  Almost every time the error looks like this :

  A/libc(11528): Fatal signal 11 (SIGSEGV), code 1, fault addr 0x9aa9f00c in tid 11637 (AsyncTask #4)

  the difference between two errors is the number right after libc, addr number and tid number. Rarely the AsyncTask number varies - i received #1 couple times but I was unable to reproduce it.

  Question

  How can i avoid this error ? What can be the source of it ?

• How do I remux/transcode a progressive file in ffmpeg ?

  3 décembre 2014, par Levi Roberts

  Here’s what I’m trying to do.

  My primary objective is to remux or transcode a currently downloading media file for AppleTV and iOS compatible streaming.

  I am doing this by looking at the media file and only transcoding when necessary, otherwise it will only alter the container the video/audio lives in. This will reduce overhead for files that are already compatible. The specific compatible output I am looking for is AppleTV3 and iOS.

  I have a file that is progressive, meaning that it is downloading using another download manager or another app without the help of nodejs. This file may or may not have the moov information available in the beginning of the file. It just so happens, that I believe my test file does.

  I have some code that is partially working and it would make sense to be able to get this code fully working. That said, I’m not dismissing alternative ways to do this.

  My primary problem (I think) has to do with the moov header location or that it’s being set incorrectly. I’m hoping the fix is as simple as correcting my poor ffmpeg knowledge with command line parameters.

  I am piping the file to and from ffmpeg via GrowingFile and fs.createWriteStream respectively.

  My code for doing so is :

  var fs = require('fs');
  
  var child = require('child_process');
  
  
  
  var GrowingFile = require('growing-file');
  
  var input_file = GrowingFile.open('./tmp/input.mp4');
  
  var output_file = fs.createWriteStream('./tmp/output.m4v');
  
  
  
  // I've tried various args and ffmpeg params here without success.
  
  var args = ['-re', '-i', 'pipe:0', '-g', '52', '-ab', '64k', '-vcodec', 'libx264', '-vb', '448k', '-f', 'mp4', '-movflags', 'frag_keyframe+faststart', 'pipe:1'];
  
  var trans_proc = child.spawn('ffmpeg', args, null); 
  
  
  
  input_file.pipe(trans_proc.stdin);
  
  trans_proc.stdout.pipe(output_file);

  I am also temporarily trying to make these files work as intended via ffmpeg command line alone, without success. That command is :

  ffmpeg -i original.mp4 -vcodec copy -r 24 output.m4v

  Snippet of original.mp4 via mediainfo :

  General
  
  Format                                   : MPEG-4
  
  Format profile                           : Base Media / Version 2
  
  Codec ID                                 : mp42
  
  File size                                : 9.87 MiB
  
  Duration                                 : 43mn 14s
  
  Overall bit rate mode                    : Variable
  
  Overall bit rate                         : 31.9 Kbp
  
  
  
  Video
  
  Format                                   : AVC
  
  Format/Info                              : Advanced Video Codec
  
  Format profile                           : High@L2.1
  
  Codec ID                                 : avc1
  
  Duration                                 : 43mn 14s
  
  Width                                    : 480 pixels
  
  Height                                   : 268 pixels
  
  Color space                              : YUV
  
  Scan type                                : Progressive
  
  Stream size                              : 67.5 MiB
  
  
  
  Audio
  
  Format                                   : AAC
  
  Format/Info                              : Advanced Audio Codec
  
  Format profile                           : LC
  
  Codec ID                                 : 40
  
  Duration                                 : 43mn 14s
  
  Bit rate mode                            : Variable
  
  Bit rate                                 : 96.0 Kbps

  What’s happening is that output.m4v has an incorrect duration of only the part of the file that’s already downloaded. The video reaches the end or a refresh happens to make the duration longer. This process repeats until the original file is done downloading. What I want is to be able to emulate/clone the duration of the input file to the output file .