Recherche avancée

Sur d’autres sites (4490)

• FFMPEG API - Recording video and audio - Syncing problems

  16 juin 2016, par Solidus

  I’m developing an app which is able to record video from a webcam and audio from a microphone. I’ve been using QT but unfortunately the camera module does not work on windows which led me to use ffmpeg to record the video/audio.

  My Camera module is now working well besides a slight problem with syncing. The audio and video sometimes end up out of sync by a small difference (less than 1 second I’d say, although it might be worse with longer recordings).

  When I encode the frames I add the PTS in the following way (which I took from the muxing.c example) :

  • For the video frames I increment the PTS one by one (starting at 0).
  • For the audio frames I increment the PTS by the nb_samples of the audio frame (starting at 0).

  I am saving the file at 25 fps and asking for the camera to give me 25 fps (which it can). I am also converting the video frames to the YUV420P format. For the audio frames conversion I need to use a AVAudioFifo because the microfone sends bigger samples than the mp4 stream supports, so I have to split them in chuncks. I used the transcode.c example for this.

  I am out of ideas in what I should do to sync the audio and video. Do I need to use a clock or something to correctly sync up both streams ?

  The full code is too big to post here but should it be necessary I can add it to github for example.

  Here is the code for writing a frame :

  int FFCapture::writeFrame(const AVRational *time_base, AVStream *stream, AVPacket *pkt) {
  
      /* rescale output packet timestamp values from codec to stream timebase */
  
      av_packet_rescale_ts(pkt, *time_base, stream->time_base);
  
      pkt->stream_index = stream->index;
  
      /* Write the compressed frame to the media file. */
  
      return av_interleaved_write_frame(oFormatContext, pkt);
  
  }

  Code for getting the elapsed time :

  qint64 FFCapture::getElapsedTime(qint64 *previousTime) {
  
      qint64 newTime = timer.elapsed();
  
      if(newTime > *previousTime) {
  
          *previousTime = newTime;
  
          return newTime;
  
      }
  
      return -1;
  
  }

  Code for adding the PTS (video and audio stream, respectively) :

  qint64 time = getElapsedTime(&previousVideoTime);
  
  if(time >= 0) outFrame->pts = time;
  
  //if(time >= 0) outFrame->pts = av_rescale_q(time, outStream.videoStream->codec->time_base, outStream.videoStream->time_base);
  
  
  
  qint64 time = getElapsedTime(&previousAudioTime);
  
  if(time >= 0) {
  
      AVRational aux;
  
      aux.num = 1;
  
      aux.den = 1000;
  
      outFrame->pts = time;
  
      //outFrame->pts = av_rescale_q(time, aux, outStream.audioStream->time_base);
  
  }

• Opus Audio Codec in Linphone Android 2013 Version

  2 septembre 2015, par Redturbo

  I want to just enabled Opus Audio Codec in my VOIP application, I have try code from here : http://stackoverflow.com/questions/31635522/force-using-just-opus-codec-in-linphone-android/31652551#31652551

  I try to check findpayloadtype first :

  for (PayloadType pt : mLc.getAudioCodecs()) {
  
                  pt = mLc.findPayloadType("PCMA", 8000, 1);
  
                  Log.d("LinphoneManager", "PayloadType PCMA : " + pt);
  
              }
  
  
  
              for (PayloadType pt : mLc.getAudioCodecs()) {
  
                  pt = mLc.findPayloadType("PCMU", 8000, 1);
  
                  Log.d("LinphoneManager","PayloadType PCMU : "+pt);
  
              }
  
  
  
              for (PayloadType pt : mLc.getAudioCodecs()) {
  
                  pt = mLc.findPayloadType("OPUS", 8000, 1);
  
                  Log.d("LinphoneManager","PayloadType P : "+pt);
  
  
  
              }

  PCMA and PCMU show value in log :

  [PCMA] clock [8000], bitrate [64000]

  [PCMU] clock [8000], bitrate [64000]

  but OPUS show null value :

  null

  is that something wrong with my code to got OPUS audio codec, or something else ?

• How to add an arbitrary, formatted timestamp to a video with FFMPEG ?

  3 septembre 2015, par Neil M.

  I am calling ffmpeg from a custom tool to concatenate video files while overlaying a timestamp in the output. The output video needs to have a timestamp starting at an arbitrary time. The format must be a 12-hour clock with seconds and meridiem, e.g. 10:34:59 AM or 6:13:09 PM. Here’s the full command I’m using right now :

  ffmpeg\bin\ffmpeg.exe -y -i "concat:input.mod" -ss 00:00:00 -t 00:02:17 
  
  -an -vcodec libx264 -profile:v baseline -level 13 -b:v 2000k -vf 
  
   "drawtext=fontcolor=white:fontsize=16:fontfile="/Windows/Fonts/arial.ttf":
  
  box=1:boxcolor=black@0.3:x=(w-text_w-10):y=(h-text_h-5):
  
  timecode='02\:36\:17\;00':rate=30000/1001" output.mp4

  This outputs a 2 minute, 17 second duration video beginning at the start of the input file. The output video has a timecode in the bottom-right corner beginning at the time 02:36:17 and ending at 02:38:34. What I want is exactly this, but instead of printing "02:36:17 ;00" on frame 0 and counting up from there, it should print "2:36:17 AM" on frame 0 and count up from there.

  I have tried using the localtime function to output formatted time, but the time value it uses is the time that the drawtext filter is called. It doesn’t take a parameter for an arbitrary time.

  I have also looked at the pts function, which seems to allow an arbitrary offset but only supports two formatting options, neither of which is the clock format I need.

  What is the proper way to add a timestamp with an arbitrary starting time and format using ffmpeg ?