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• How can you extract the header data of an audio file using libav ?

  16 janvier 2024, par CheekyChips

  I'm using libav/ ffmpeg to transcode an audio file from one format to another in c++. I have written it in a way so that it works for receiving streamed audio, where first the header of an audio file is sent, followed by chunks of encoded audio.

  


  Now I'd like to generate some test files, where I separate an existing audio file into the header component, followed by chunks of encoded audio data, preferably frame aligned. (I would store this as base64 text for readability with each piece separated by some token, e.g. a newline character)

  


  Is it possible using ffmpeg/ libav to extract the raw data of the header of an audio file ? If not, does anyone have any suggestions for how I can find the point in the audio file between the header data and the audio data, so I can then split it at this point ?

  


  Note : actually if this is possible using the tool ffmpeg that would also be a viable solution

  


• Accessing data of fmmpeg while processing in node.js

  25 juin 2019, par newCOder2137ssh

  Im converting a .mp4 file with ffmpeg to a .mp3 file.I am only able to access this data after ffmpeg finished, but I want to access it while it is processing.

  I am currently using fluent-ffmpeg to process the video. This is how I process it :

  proc = new ffmpeg({
  
      source: stream
  
  })
  
  proc.withAudioCodec('libmp3lame')
  
      .toFormat('mp3')
  
      .seekInput(35)
  
      .output(audio)
  
      .run();

  I can access the data after ffmpeg fiinished with proc.on('end', ()) but I’d like to access the data while it’s processing and make a reeadable Stream out of it. Does someone know how to do that ?

• Synchronization between camera video and inertial sensor data

  14 janvier 2013, par Dima Bobby

  I need to :

  write an Android real-time data logging application employing camera video and polling other sensor (accelerometer, gyro, compass) data at high rates e.g. 50 Hz and writing this information into file. As these data will later be used for navigation, precise synchronization between different data is extremely important.

  What I have done :

  implemented sensor polling in native code, so that less Java execution overhead is employed. Nonetheless, camera encoding is still in Java, for this I tried MediaRecorder and MediaCodec. In both cases data from inertial sensors and camera are not synchronized between each other, there is a varying delay of about 400ms and this is inacceptible. Moreover, I am pretty sure that encoding is HW accelerated. Now, to reach my goal I am considering about going for native implementation of video encoding using either OpenCV or FFMPEG (native code is expected to be more efficient).

  EDIT : I have even tried saving the image uncompressed as pgm file, but this way the image data get really huge in size and the FPS is really low, so we are losing data. I suspect that file writing process is the bottleneck in this case. Is there an efficient way to save raw data to file achieving high FPS ?

  Any hints what I should go for to achieve my goal ? I am using Android Jelly Bean with Asus Transformer TF700 Infinity.

  Regards,
  Dmitriy