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• Noise when decoding mp3 using libavcodec on iOS

  11 janvier 2014, par Trenskow

  I have this methods. It first sets up an audio input if necessary. Then it reads a frame, and returns the frame converted using an AudioConverterRef (wrapped in an KFInlineConverterUnit class) to my Core Audio graph. At the end of the method it tears down the input, if audio output has stopped.

  - (NSData *)readNextChunk {
  
  
  
      /* Setup audio input */
  
      if (_formatContext == NULL && self.runLoopActive) {
  
  
  
          static dispatch_once_t onceToken;
  
          dispatch_once(&onceToken, ^{
  
              av_register_all();
  
          });
  
  
  
          avformat_network_init();
  
  
  
          av_init_packet(&_packet);
  
  
  
          _formatContext = avformat_alloc_context();
  
  
  
          [self handleError:avformat_open_input(&_formatContext, [[_url absoluteString] cStringUsingEncoding:NSUTF8StringEncoding], NULL, NULL)];
  
  
  
          [self handleError:avformat_find_stream_info(_formatContext, NULL)];
  
  
  
          _audioStreamIndex = -1;
  
          for (NSInteger index = 0 ; index < _formatContext->nb_streams ; index++)
  
              if (_formatContext->streams[index]->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
  
                  _audioStreamIndex = index;
  
                  break;
  
              }
  
  
  
          if (_audioStreamIndex > -1) {
  
  
  
              _codec = avcodec_find_decoder(_formatContext->streams[_audioStreamIndex]->codec->codec_id);
  
  
  
              _codecContext = _formatContext->streams[_audioStreamIndex]->codec;
  
  
  
              [self handleError:avcodec_open2(_codecContext, _codec, NULL)];
  
  
  
          }
  
  
  
          if (self.timeOffset > .0) {
  
              int64_t timestamp = AV_TIME_BASE * self.timeOffset;
  
              av_seek_frame(_formatContext, -1, timestamp, AVSEEK_FLAG_ANY);
  
          }
  
  
  
      }
  
  
  
      /* Read and decode next frame */
  
  
  
      NSData *chunk = nil;        
  
      AVFrame *frame = avcodec_alloc_frame();
  
      while (self.runLoopActive && _formatContext != NULL && av_read_frame(_formatContext, &_packet) >= 0) {
  
  
  
          if (_packet.stream_index == _audioStreamIndex) {
  
  
  
              int gotFrame = 0;
  
              int len = avcodec_decode_audio4(_codecContext, frame, &gotFrame, &_packet);
  
              [self handleError:len];
  
  
  
              if (gotFrame) {
  
  
  
                  /* Setup a converter for my Audio Graph */
  
                  AudioStreamBasicDescription inputAudioDescription = [self audioDescriptionForCodecContext];
  
  
  
                  if (!_converter || memcmp(&inputAudioDescription, _converter.inputAudioDescription, sizeof(AudioStreamBasicDescription)) != 0)
  
                      _converter = [KFInlineConverterUnit newWithInputAudioDescription:inputAudioDescription
  
                                                                outputAudioDescription:self.audioDescription];
  
  
  
                  /* Convert frames */
  
                  if (inputAudioDescription.mFormatFlags & kAudioFormatFlagIsNonInterleaved) {
  
                      NSMutableArray *buffers = [@[] mutableCopy];
  
                      for (NSInteger i = 0 ; i < frame->channels ; i++) {
  
                          [buffers addObject:[NSData dataWithBytes:frame->data[i] length:frame->nb_samples * inputAudioDescription.mBytesPerFrame]];
  
                      }
  
                      chunk = [_converter convertBuffer:buffers];
  
                  } else
  
                      chunk = [_converter convertBuffer:@[[NSData dataWithBytes:frame->data[0] length:frame->nb_samples * inputAudioDescription.mBytesPerFrame]]];
  
  
  
                  if (_packet.data != NULL)
  
                      av_free_packet(&_packet);
  
  
  
                  break;
  
  
  
              }
  
  
  
          }
  
  
  
      }
  
  
  
      avcodec_free_frame(&frame);
  
  
  
      /* Tear down if output has stopped */
  
      if (!self.runLoopActive) {
  
  
  
          avformat_free_context(_formatContext);
  
          _formatContext = NULL;
  
  
  
          avformat_network_deinit();
  
  
  
      }
  
  
  
      return chunk;
  
  
  
  }

  Basically everything is fine. I am developing this for iOS, and when I test it in the iOS Simulator everything works smoothly. It plays all audio formats with no problems.

  The problem arises, when I run the code on an actual device. Then mp3 files are audible - but VERY distorted. I have tried everything in my mind to make this work, but I cannot figure what's going wrong.

  I can say that the problem does NOT lay in the converter. I've extracted the audio before it hits the decoder, and it sounds the same. So the converter just converts the distorted audio. So I think it might be an MP3 decoder issue.

  Anyone experienced this before ?

• Batch concation of multiple videos files (Powershell)

  5 janvier 2024, par pops64

  I have clips from multiple different scenes in the same folder I was wondering if any one had a script that groups clips belonging to each scene together than pass them into ffmpeg for a concatenation and transcode. The file name pattern is uniform. And ids are separated by a hyphen with only the scene id being unique. I am currently doing this scene by scene in FFmpeg batch av converter but any help automating this in powershell would be greatly appreciated. I just can't figure out where to start

  


  {name_of_scene}-{scene_id}-{clip_id}-{resolution}.{filetype}


  


• How to decrypt .ts file with .m3u8 with key

  30 octobre 2017, par Gokul Deepak

  I have an android app which allows me to download and save videos in offline. But those files are in .ts and .m3u8 format. They are encrypted with a key.
  I can take all these files through root browser app. But I cannot view this from other than that educational android app.

  I have tried to convert using ffmpeg but it can’t encrypt because even the .key file does not show hexadecimal characters when opened from notepad. It seems encrypted. Is there any method to convert .ts files, .m3u8, .key files into a mp4 or any other formats playable by vlc.

  .key file has some chinese characters which is unusable to decrypt.
  This educational video app does not need internet to play these files so there is no dynamic keys.

  Files :

  Enc.key
  https://drive.google.com/file/d/0Byjlj5dACAM9SU5OanNhamNzSW8/view?usp=drivesdk

  980.m3u8
  https://drive.google.com/file/d/0Byjlj5dACAM9dVBPM1pNVFJiNjA/view?usp=drivesdk