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• copy .wav audio file settings to new .wav file

  18 novembre 2020, par Jonas

  currently I am working with a speech to text translation model that takes a .wav file and turns the audible speech within the audio into a text transcript. The model worked before on .wav audio recordings that were recorded directly. However now I am trying to do the same with audio that was at first present within a video.

  


  The steps are as follows :

  


  

  • retrieve a video file from a stream url through ffmpeg

  


  • strip the .aac audio from the video

  


  • convert the .aac audio to .wav

  


  • save the .wav to s3 for later usage

  


  


  The ffmpeg command I use is listed below for reference :

  


    rm /tmp/jonas/*
  ffmpeg -i {stream_url} -c copy -bsf:a aac_adtstoasc /tmp/jonas/{filename}.aac
  ffmpeg -i /tmp/jonas/{filename}.aac /tmp/jonas/{filename}.wav
  aws s3 cp /tmp/jonas/{filename}.wav {s3_audio_save_location}


  


  The problem now is that my speech to text model does not work on this audio anymore. I use sox to convert the audio but sox does not seem to grab the audio. Also without sox the model does not work. This leads me to believe there is a difference in the .wav audio formatting and therefore I would like to know how I can either format the .wav with the same settings as a .wav that does work or find a way to compare the .wav audio formatting and set the new .wav to the correct format manually through ffmpeg

  


  I tried with PyPy exiftool and found the metadata of the two files :

  


  The metadata of the working .wav file is

  


  The metadata of the .wav file that does not work is

  


  So as can be seen the working .wav file has some different settings that I would like to mimic in the second .wav file presumably that would make my model work again :)

  


  with kind regards,
Jonas

  


• FFmpeg AutoGen - set encoding settings

  6 décembre 2018, par user4964351

  I’m using FFmpeg auto generated unsafe bindings to capture rtsp (h264) stream like so :

          AVFormatContext* input_context = ffmpeg.avformat_alloc_context();
  
  
  
          AVDictionary* opts = null;
  
          ffmpeg.av_dict_set(&opts, "rtsp_transport", "tcp", 0); // set tcp transport 
  
  
  
          // try connect to rtsp stream
  
          if (ffmpeg.avformat_open_input(&input_context, "rtsp://...", null, &opts) != 0)
  
          {
  
              return;
  
          }
  
  
  
          if (ffmpeg.avformat_find_stream_info(input_context, null) < 0)
  
          {
  
              return;
  
          }
  
  
  
          // search video stream
  
          int video_stream_index = 0;
  
          for (int i = 0; i < input_context->nb_streams; i++)
  
          {
  
              if (input_context->streams[i]->codec->codec_type == AVMediaType.AVMEDIA_TYPE_VIDEO)
  
                  video_stream_index = i;
  
          }
  
  
  
          AVPacket packet;
  
          ffmpeg.av_init_packet(&packet);
  
  
  
          // create output file
  
          AVOutputFormat* format = ffmpeg.av_guess_format("mp4", null, null);
  
          AVFormatContext* output_context = null;
  
          ffmpeg.avformat_alloc_output_context2(&output_context, format, null, null);
  
          output_context->oformat = format;
  
          ffmpeg.avio_open2(&output_context->pb, "test.mp4", ffmpeg.AVIO_FLAG_WRITE, null, null);
  
  
  
           // start playing input stream
  
          ffmpeg.av_read_play(input_context);
  
          AVStream* stream = null;
  
          double stream_base_time_double = 0;
  
  
  
          var cnt = 0;
  
  
  
          // start reading packets from stream and write them to file
  
          while (ffmpeg.av_read_frame(input_context, &packet) == 0 && cnt < 200)
  
          {
  
              if (packet.stream_index == video_stream_index)
  
              {
  
                  if (stream == null) // create stream in output file
  
                  {
  
                      stream = ffmpeg.avformat_new_stream(output_context, input_context->streams[video_stream_index]->codec->codec);
  
  
  
                      // copy params from input stream
  
                      ffmpeg.avcodec_parameters_from_context(stream->codecpar, input_context->streams[video_stream_index]->codec);
  
                      stream->sample_aspect_ratio = input_context->streams[video_stream_index]->codec->sample_aspect_ratio;
  
                      // ffmpeg.av_opt_set_int(stream->codec, "crf", 25, 0); // this does not work
  
                      ffmpeg.avformat_write_header(output_context, null);
  
                  }
  
                  packet.stream_index = stream->id;
  
                  ffmpeg.av_interleaved_write_frame(output_context, &packet);
  
                  cnt++;
  
              }
  
              ffmpeg.av_packet_unref(&packet);
  
              ffmpeg.av_init_packet(&packet);
  
          }
  
  
  
          ffmpeg.av_read_pause(input_context);
  
          ffmpeg.av_write_trailer(output_context);
  
          ffmpeg.avio_close(output_context->pb);
  
          ffmpeg.avformat_close_input(&input_context);
  
          ffmpeg.avformat_free_context(input_context);
  
          ffmpeg.avformat_free_context(output_context);

  This code is working creating small test.mp4 video file.

  Now, i want to reduce file size a bit. For that i want to use crf flag.

  I can do that from command line :

  ffmpeg -rtsp_transport tcp -i rtsp://184.72.239.149/vod/mp4:BigBuckBunny_175k.mov -crf 25 F:\garbage\test.mp4

  But i can’t make it work from code.
  So far i tried setting crf like so :

  ffmpeg.av_opt_set_int(stream->codec, "crf", 25, 0);

  and

  ffmpeg.av_opt_set_int(stream->codec->priv_data, "crf", 25, 0);

  But it does nothing.

  Question : How can i set the crf option from code ?

  I know that i’m missing something obviously, but i just can’t figure it myself.

  Any help would be appreciated.

• How can I use if/else with FFmpeg to check if a video is portrait or landscape and execute different settings ?

  27 septembre 2023, par Maaaaaars

  I'm using FFmpeg to generate previews for the videos added to my website. The site script's (KVS) built-in tools help to some extent by automatically creating previews with the following properties :

  


  

  • Max. duration : 15s

  


  • Offset from beginning : 10%

  


  • Offset from end : 10%

  


  • Fragments : 5 (each lasting about 3s)

  


  • Crossfade between fragments : 1s

  


  


  However, I don't know how to recreate those through the FFmpeg command line, in addition to adding an if/else part that will check if the video is landscape or portrait.

  


  If the video is landscape, the previous properties should execute and generate the preview.

  


  If the video is portrait, I'd like to execute the previously-listed properties as well as additional ones to insert a blurred video in the background.

  


  I'm using the following command line for that, and it generates exactly what I had in mind.

  


  ffmpeg -i source-video.mp4 -vf split[original][copy];[copy]scale=ih*16/9:-1,crop=h=iw*9/16,gblur=sigma=20[blurred];[blurred][original]overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2 new-video.mp4


  


  I'm also using the following flags, which I'd like to apply to the preview video regardless of orientation.

  


  -c:v libx264 -c:a copy -movflags +faststart -preset veryfast -strict 0 -f mp4


  


  I found several unrelated solutions on if/else but none of them really match what I'm trying to achieve and only add to the confusion.

  


  Note : I am not using PHP, Python, or otherwise, and would like to know whether it's achievable only through the FFmpeg command line itself.