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• ffmpeg : How to set AVFormatContext from NSData

  21 janvier 2014, par SUKIYAKI

  I'm using FFmpeg library in Objective-C.

  I want to set AVFormatContext from NSData which contain imagedata.
  I know I can set AVFormatContext with av_open_input_file().
  so writing contents of NSData to a temporary file, I can do it like this.

  [data writeToFile:@"./temp.mov" atomically:YES];
  
  av_open_input_file(&pFormatCtx, "./temp.mov", NULL, 0, NULL);
  
  
  
  .
  
  .
  
  .
  
  
  
  NSFileManager *fm = [NSFileManager defaultManager];
  
  [fm removeFileAtPath:@"./temp.mov" handler:nil];

  but, I don't want to use temporary file.

  Does anyone know smart way ?

  sorry my poor English.

  Thanks

• Building ffmpeg iOS libraries for armv7, armv7s, arm64, i386 and universal

  4 février 2015, par sandy

  I have seen several scripts to build FFmpeg API for armv7, 7s and i386 but couldn’t find anything which would work for armv64 as well. Some of the answers on other threads of this forum suggested to prepare a separate library for arm64 but it does not work well with rest of the architectures. Hence I need a script which can work for all the supported architectures for iOS including armv7, armv7s, armv64 and i386.

• ffmpeg convert variable framerate .webm to constant framerate video

  4 novembre 2019, par Dashadower

  I have a .webm file of a recording of a game at 16fps. However, upon trying to process the video with OpenCV, it seems the video is recorded with a variable framerate, so when I try to use OpenCV to get a frame every second by getting the every 16th frame, it won’t work since the video stream will end prematurely.

  Therefore, I’m trying to convert a variable-frame .webm video, which claims it has a framerate of 16 fps, to a video with a constant frame, so I can extract one frame for every second. I’ve tried the following ffmpeg command from https://ffmpeg.zeranoe.com/forum/viewtopic.php?t=5518 :

  ffmpeg -i input.webm -c:v copy -b:v copy -r 16 output.webm

  However, the following error will occur :

  [NULL @ 00000272ccbc0c40] [Eval @ 000000bc11bfe2f0] Undefined constant or missing '(' in 'copy'
  
  [NULL @ 00000272ccbc0c40] Unable to parse option value "copy"
  
  [NULL @ 00000272ccbc0c40] Error setting option b to value copy.
  
  
  
  Error setting up codec context options.

  Here’s is the code I’m trying to use to process a frame every second :

  video = cv2.VideoCapture(test_mp4_vod_path)
  
  print("Opened ", test_mp4_vod_path)
  
  print("Processing MP4 frame by frame")
  
  
  
  # forward over to the frames you want to start reading from.
  
  # manually set this, fps * time in seconds you wanna start from
  
  video.set(1, 0)
  
  success, frame = video.read()
  
  #fps = int(video.get(cv2.CAP_PROP_FPS))  # this will return 0!
  
  fps = 16  # hardcode fps
  
  total_frame_count = int(video.get(cv2.CAP_PROP_FRAME_COUNT))
  
  print("Loading video %d seconds long with FPS %d and total frame count %d " % (total_frame_count/fps, fps, total_frame_count))
  
  
  
  count = 1
  
  while video.isOpened():
  
      success, frame = video.read()
  
      if not success:
  
          break
  
  
  
      if count % fps == 0:
  
          print("%dth frame is %d seconds on video"%(count, count/fps))
  
      count += 1

  The code will finish before it gets near the end of the video, since the video isn’t at a constant FPS.
  How can I convert a variable-FPS video to a constant FPS video ?