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• Encoded images into H264 video are skipped and/or missing ?

  25 juillet 2013, par Jona

  I'm trying to encode images into an H264 MP4 video. The issues I'm having is that some of the images are skipped or at the end of the video simply missing. I need the video to play every single image I encode since it is an animation.

  Any help setting the encoder properly would be greatly appreciated !

  Encoder settings :

  AVCodecContext *c;
  
  ...
  
  c->codec_id = AV_CODEC_ID_H264;
  
  c->bit_rate = mOutputWidth*mOutputHeight*4;//400000;
  
  /* Resolution must be a multiple of two. */
  
  c->width    = mOutputWidth;
  
  c->height   = mOutputHeight;
  
      /* timebase: This is the fundamental unit of time (in seconds) in terms
  
       * of which frame timestamps are represented. For fixed-fps content,
  
       * timebase should be 1/framerate and timestamp increments should be
  
       * identical to 1. */
  
  c->time_base.den = mFps;
  
  c->time_base.num = 1;
  
  c->gop_size      = 12; /* emit one intra frame every twelve frames at most */
  
  c->pix_fmt       = AV_PIX_FMT_YUV420P;
  
  ...
  
  av_dict_set(&pOptions, "preset", "medium", 0);
  
  av_dict_set(&pOptions, "tune", "animation", 0);
  
  
  
  /* open the codec */
  
  ret = avcodec_open2(c, codec, &pOptions);
  
  if (ret < 0) {
  
      LOGE("Could not open video codec: %s", av_err2str(ret));
  
      return -1;
  
  }

  Update 07/24/13 :
  I was able to achieve a better video by setting the gop_size=FPS and writing the last video frame repeatedly FPS+1 times seemed to resolve all issues. To me it seems odd to do that but might be something standard in the video encoding world ? Any tips feedback about this ?

• FFmpeg GPU 10-bit HEVC encoding using NVENC

  10 avril 2021, par chronosynclastic

  I'm encoding some 4K 10-bit YUV test sequences using NVENC HEVC encoder. For an example sequence and configuration, I use the following command.

  



  ffmpeg -hide_banner -benchmark -loglevel debug -y -f rawvideo -s:v 3840x2160 -r 50 -pix_fmt yuv420p10le -i ParkRunning3_3840x2160_50fps_10bit_420.yuv -c:v hevc_nvenc -preset hp -rc cbr -profile:v main10 -b:v 10M output.mp4


  



  My goal is to achieve as low latency as possible ; therefore I set the preset to low-latency high-performance. However, I only get around 15 fps encoding speed with this command. A logfile from the ffmpeg output from the above command is here.

  



  I also tried with different presets and different sequences. The results are similar for all the 10-bit sequences I encoded. For 1920x1080 10-bit sequences, I get around 50-60 fps with HEVC encoder. But for 8-bit sequences I'm getting a much higher throughput of around 450-500 fps with similar preset and rate control modes. In the example, I'm using CBR as rate-control mode but I also tested and obtained similar results (in terms of encoding throughput) with VBR and constant QP modes.

  



  Is there anything I'm missing in my command for 10-bit HEVC encoding ? I understand that with 10-bit, because of the increased bit-depth, the encoding will take longer. But a reduction in throughput on this scale makes me think that I'm doing something wrong. It seems that FFmpeg is inserting an auto_scaler before the encoder which converts from yuv420p10le (my input format) to p010le (the 10-bit format accepted by NVENC). Could this scaling module reduce the encoder speed so drastically ?

  


• Ffmpeg mixing audio only for n number of videos using offset with an altered duration

  26 août 2022, par Turgut

  I want to mix audio stream of n amount of video files with ffmpeg, with certain parameters such as :

  


  

  • Duration : I want to specify how long each audio is going to play for each output. For example if I specify ffmpeg -i -d:5 first.mp4 -i second.mp4 it should play the audio from first.mp4 for 5 seconds (I don't know if -d:5 is a real tag it's just an example I've made ).

  


  • Starting point : I want to specify when a given file is going start on the output, I probably need to use -itsoffset 5 but I don't know if it's the right one in terms of interacting with other commands, in on itself it works fine. For example : ffmpeg -i -isoffset 5 first.mp -i second.mp4 causes the second.mp4 to start immediately, and first.mp4 to start after 5 seconds.

  


  • Segmentation : This is the tricky one, I want to specify at which point the input's audio should start. It's like the -ss flag but the problem is it's not working together with -itsoffset. For example when I say ffmpeg -i -ss 5 first.mp4 -i second.mp4 both files should start immediately on the output, but first.mp4 should start on it's 5 seconds. So the 5th second of first.mp4 is heard at the 1st second of the output.

  


  


  This is what I'm trying to achieve, my problem is that I don't know how to implement 'duration' and -ss is not working together with -itsoffset.

  


  At the end I should have something similar to this :

  


  ffmpeg -y -d 5 -itsoffset 3.5 -i first.mp4 -d 10 -ss 10 -itsoffset 5.3 -i 3 -vn -copyts -async 1 -filter_complex amix=inputs=2 out.mp


  


  Which should result in an audio that sounds like this : The first 3.5 seconds are empty, no audio is heard. Then first.mp4 is heard from it's beginning for 5 seconds. When the outputs timestamp reaches 5.3, the 10th seconds of second.mp4 is heard (while first.mp4 is still playing, it's supposed to play until 8.5, so I should hear both files at the same time.) for 10 seconds.

  


  I can't find an example of this and some sources are out-of date.