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• Do avcodec_receive_frame and avcodec_send_packet block / how to design ffmpeg decoding loop ?

  12 octobre 2020, par Paprika

  I'm thinking about how to design a loop that reads frames from internet, feed to ffmpeg decoder and then receive from ffmpeg to send to a render.

  


  Take this pseudocode loop in consideration :

  


  while true {
    auto packet = receive_packet_from_network();
    avcodec_send_packet(packet);
    auto frame = alloc_empty_frame();
    int r = avcodec_receive_frame(&frame);
    if (r==0) {
        send_to_render(frame);
    }
}


  


  do avcodec_send_packet or avcodec_receive_frame block or ffmpeg has an internal thread ? I'm concerned about this loop because it waits for packets from network, so it has some delay. I'd like to do something like this instead :

  


  //thread 1
while true {
    auto packet = receive_packet_from_network();
    avcodec_send_packet(packet);
}
//thread 2
while true {
    auto frame = alloc_empty_frame();
    int r = avcodec_receive_frame(&frame);
    if (r==0) {
        send_to_render(frame);
    }
}


  


  however, now, if avcodec_receive_frame does not block, then this loop would run too fast, millions of times per second.

  


  So, how should I design the send/receive of packets in ffmpeg in the most efficient way ? I don't want to spend cpu cycles like in the thread2 loop.

  


• Preview video in android before saving to phone

  13 novembre 2014, par Zoe

  I’m in the process of creating a video editor for android.
  I am loading .mp4 videos into a timeline, where each rectangle in the timeline represents an imported video and I can drag/drop and rearrange these videos etc before saving the new .mp4 to my phone.

  I’ve been using mp4parser to do this, however I have ffmpeg loaded too but have avoided using this as I’m not too familiar with c++

  I have a space for a video player in my app. The idea is to have a seek line that can be dragged along the timeline as you are editing, and I want the player to be able to play a
  the edited video at the given point.

  However, the only examples on how to implement video players in android require you to load this video from your phone to play it. I was thinking I could just play the loaded videos separately but one after another giving the impression you’re watching a whole video, but I’m later planning to add functionality to include transitions and subtitles to videos which you would not be able to preview using this method.

  Any ideas on how about I can go about implementing a video player to preview the media whilst editing ?

  Thank you.

• FFmpeg C++ APIs to detect if a video is rotated (shot on phone)

  11 mars 2016, par williamtroup

  Using the FFmpeg C++ API, is there a way to determine if a video was shot on a phone and if its rotated ?

  When extracting the frames, the are rotated at a 90 degree angle, which is fine, but it would be good to report back that the video is rotated.