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• FFmpeg convert time to frame

  3 décembre 2013, par William Seemann

  Does anyone know how to convert a timestamp into a frame ? For example, if I wanted the frame number at 2 seconds in a video with a framerate of 30/fps it would be the 60th frame. Here is the code I have so far. However, I don't think it's correct since seek_time has a value of 90 (for a 1 sec target) using a video with a framerate of 23.98 :

  int timeUs = 1000000; // 1 sec
  
  AVPacket packet;
  
  AVPacket *pkt = NULL;
  
  int64_t desired_frame_number = -1;
  
  
  
  State *state = *ps;
  
  
  
  Options opt = option;
  
  
  
  int stream_index = state->video_stream;
  
  int64_t seek_time = av_rescale_q(timeUs, AV_TIME_BASE_Q, state->pFormatCtx->streams[stream_index]->time_base);
  
  int64_t seek_stream_duration = state->pFormatCtx->streams[stream_index]->duration;
  
  
  
  int flags = 0;
  
  int ret = -1;
  
  
  
  // Convert time into frame number
  
  seek_time /= 1000;
  
  printf("seek time: %" PRId64 "\n", seek_time);

• Extracting all frames of a video using ffmpeg

  4 décembre 2013, par Gonzalo Solera

  I'm trying to extract all the frames of a video using ffmpeg compiled statically for android. I want to extract all the frames with a lower quality (at jpg format) and then, select the specific frames I want with a higher resolution and extract them at png format.
  But the problem is that I need to know exactly at what time is placed the selected frame in order to be able to extract te same frame at higher resolution. When I calcule how much time are between frames (duration_of_the_video/total_frames_extracted) and I multiple it by the number of the frame I want to extract again, the result time isn't the exact time of the frame.

  How could I extract a specific number of frames of a video using ffmpeg ? I'm trying to extract all the frames but sometimes not all the frames are extracted. For example, I have a 1600 ms long video but when I use this command :

  ffmpeg -i file.mp4 -y %d.jpg

  it doesn't extract all the frames because it only extracts 45 frames but the frame rate is 30 fps (1600/45 = 35.5555 and 1000/30 = 33.33333).

  So, in order to be able to calculate at what time is placed the frame I want, I would need to extract ALL the frames of the video or extract a fixed number of frames (it doesn't matter if some frames are repeated if I can get the time of them).

  This is the output when I try to extract all the frames (there should be 48 but there are 45 instead so I can't calculate the exact time...)
  

  I'm not sure If I have explained correctly but I will appreciate any help. Thanks !

• FFmpeg not decreasing

  19 avril 2018, par David

  I need ffmpeg to transform a video stream into images and reduce their size only if they don’t fit in a 1000x1000 box.

  My issue is that if the image is smaller, ffmpeg increases the size of the image to 1000 in width or height, whereas I don’t want small images to be upscaled. The force_original_aspect_ratio=decrease does not seem to work here. Any ideas why ?

  Here is my shell command :

  ffmpeg -i 'rtsp://184.72.239.149/vod/mp4:BigBuckBunny_175k.mov' -r 5 -vf scale=w=1000:h=1000:force_original_aspect_ratio=decrease -f image2 -qscale:v 1 ./output_%01d.jpg