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• Create a demultiplexer for MPEG 2 TS in android

  17 novembre 2014, par anz

  I have a requirement where I need to extract ID3 tags from a MPEG2 TS(HLS STREAM). MPEG2 has a limited support in android in regards to playing the file. But my concern is to extract the ID3 tags(playing the file is not necessary). Hence I am not concerned with the codecs(encoding and decoding).

  I have explored the following options :

  libstagefright and OpenMax : A playback engine implemented by Google from Android 2.0.
  It has a MediaExtractor is responsible for retrieving track data and the corresponding meta data from the underlying file system or http stream. But according to this post Adding video codec to Android I need to build my own firmware or my own media player.I am hoping I don’t have to go down that path. More info on stagefright and openMax can be found here :

  An overview of Stagefright player

  Android’s Stagefright Media Player Architecture

  Custom Wrapper Codec Integration into Android

  How to integrate a decoder to multimedia framework

  Compiling and using FFMPEG : A complete, cross-platform solution to record, convert and stream audio and video. We can demultiplex ts files with this library as mentioned here :

  FFmpeg - Extracting video and audio from transport stream file (.ts).

  But I am not sure if I will be able to extract the ID3 tags from the HLS Stream. libavformat might be able to do this but I still need to come up with a mechanism for signaling the read metadata to my application.

  Compiling vlc for android : I have compiled vlc for android and made some modifications inside the transport module in demux component for extracting the tags, but it is not able to play all the streams that I am supplying to it.

  After looking through these options , I am still at a fix in how to achieve this. I don’t want to create a media player as I will not be playing the files nor do I want to build my own firmware. Using ffmpeg seems to be the most viable option, but I want to try this without using any third-party or open source library. My questions are :

  Is it even possible to create a demultiplexer from scratch that will work on android ?

  If possible then ,how to go about it ?

  Any options that I have missed ?

  I am new to this. Any help would be greatly appreciated..Thanks

• av_write_frame fails when encoding a larger audio file to .mpg

  27 novembre 2012, par TheSHEEEP

  I am encoding live rendered video data and an existing .wav file into an mpg-file.

  To do that I first write all audio frames, and then the video frames as they come in from the render engine. For smaller .wav files (< 25 seconds), everything works perfectly fine. But as soon as I use a longer .wav file, av_write_frame (when writing the audio frame) just returns -1 after having written some 100 frames. It is never the same frame at which it fails, also it is never the last frame.
  All test files can be played perfectly with any player I tested.

  I am following the muxing example (more or less).

  Here is my function that writes an audio frame :

  void write_audio_frame( Cffmpeg_dll * ptr, AVFormatContext *oc, AVStream *st, int16_t sample_val )
  
  {
  
  AVCodecContext *c;
  
  AVPacket pkt = { 0 }; // data and size must be 0;
  
  AVFrame *frame = avcodec_alloc_frame();
  
  int got_packet;
  
  
  
  av_init_packet(&pkt);
  
  c = st->codec;
  
  
  
  get_audio_frame(ptr, ptr->samples, ptr->audio_input_frame_size, c->channels);
  
  frame->nb_samples =  ptr->audio_input_frame_size;
  
  int result = avcodec_fill_audio_frame(frame, c->channels, c->sample_fmt,
  
                          (uint8_t *) ptr->samples,
  
                           ptr->audio_input_frame_size *
  
                          av_get_bytes_per_sample(c->sample_fmt) *
  
                          c->channels, 0);
  
  if (result != 0)
  
  {
  
      av_log(c, AV_LOG_ERROR, "Error filling audio frame. Code: %i\n", result);
  
      exit(1);
  
  }
  
  
  
  result = avcodec_encode_audio2(c, &pkt, frame, &got_packet);
  
  if (result != 0)
  
  {
  
      av_log(c, AV_LOG_ERROR, "Error encoding audio. Code: %i\n", result);
  
      exit(1);
  
  }
  
  
  
  
  
  if (c->coded_frame && c->coded_frame->pts != AV_NOPTS_VALUE)
  
      pkt.pts= av_rescale_q(c->coded_frame->pts, c->time_base, st->time_base);
  
  pkt.flags |= AV_PKT_FLAG_KEY;
  
  
  
  pkt.stream_index= st->index;
  
  av_log(c, AV_LOG_ERROR, "Got? %i Pts: %i Dts: %i Flags: %i Side Elems: %i Size: %i\n", 
  
          got_packet, pkt.pts, pkt.dts, pkt.flags, pkt.side_data_elems, pkt.size);
  
  
  
  /* write the compressed frame in the media file */
  
  result = av_write_frame(oc, &pkt);
  
  if (result != 0) 
  
  {
  
      av_log(c, AV_LOG_ERROR, "Error while writing audio frame. Result: %i\n", result);
  
      exit(1);
  
  }
  
  }

  So "Error while writing audio frame. Result : -1" is what I always get after some frames.

  And here is my get_audio_frame function :

  void get_audio_frame( Cffmpeg_dll* ptr, int16_t* samples, int frame_size, int nb_channels, int16_t sample_val ) 
  
  {
  
      fread( samples, sizeof( int16_t ), frame_size * nb_channels, ptr->fp_sound_input );
  
  };

  And finally, this is the loop in which I write all audio frames (don't worry about the .wav header, I skipped it before that loop) :

  while (!feof(ptr->fp_sound_input))
  
      {
  
          write_audio_frame( ptr, ptr->oc, ptr->audio_st, -1 );
  
      }

  As you can see, I'm outputting almost everything in the packet and check for any possible error. Other than av_write_frame failing after some time when I am encoding a longer audio file, everything seems perfectly fine. All the packet values I am tracking are 100% the same for all frames (except the data pointer, obviously). Also, as stated, the same procedure works flawlessly for shorter fp_sound_input files. avcodec_encode_audio2() and avcodec_fill_audio_frame() also never fail.

  The codecs I use for encoding are CODEC_ID_MPEG2VIDEO (video) and CODEC_ID_MP2 (audio). The .wav files are saved in PCM 16 LE (all use the exact same encoding).

  What could be wrong here ?

• Get remote MKV file metadata using nodejs

  31 mars 2024, par Ali Rahmani

  I need to extract the softsubs embeded into an mkv file hosted on a remote server using nodejs.

  &#xA;

  All of the solutions I've found online so far are using local files, and others are either poorly documented or throwing unknown errors that I can't find online ; That doesn't work for me. I need to extract subtitles from the remote file (like http://some-url.com/videos/video.mkv) without downloading the entire file to use it in my web-based application.

  &#xA;