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• How Opensl es on android control the audio speed ?

  6 décembre 2013, par user1882379

  I use NDK+FFMPEG on android to decode an video file, and transfer the decoded pcm data to opensles for play audio .I register the opengles for the pcm format：

    SLDataFormat_PCM format_pcm;
  
      format_pcm.formatType = SL_DATAFORMAT_PCM;
  
      format_pcm.numChannels = channel;
  
      format_pcm.samplesPerSec = rate * 1000;
  
      format_pcm.bitsPerSample = SL_PCMSAMPLEFORMAT_FIXED_16;
  
      format_pcm.containerSize = SL_PCMSAMPLEFORMAT_FIXED_16;

  also I convert the decoded pcm data to AV_SAMPLE_FMT_S16 format using swr_convert(...), but the play audio speed is very fast. but if you use sdl , the play speed is normal. It would be sdl can control the play audio speed, but opensles can not. I do not know whether it is my mistake using opensles or opensles can not control audio speed(need application to control)？

• 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 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);