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• How to 'convert' MP3 file to numpy array or list

  30 mai 2021, par Ajayi Olamide

  I'm working on an audio-related project that connects with Django backend via rest api. Part of the front-end requires to display waveforms of associated mp3 files and for this, it in turn requires optimized data of each mp3 file in form of an array, which the front-end (javascript) then processes and converts to a waveform. I can pick the associated mp3 file from backend storage, the problem is converting it into an array which I can serve to the front-end api. I have tried several methods but none seem to be working. I tried this How to read a MP3 audio file into a numpy array / save a numpy array to MP3 ? which leaves my computer hanging until I forced it to restart by holding the power button down. I have a working ffmpeg and so, I have also tried this Trying to convert an mp3 file to a Numpy Array, and ffmpeg just hangs which continues to raise TypeError on np.fromstring(data[data.find("data")+4:], np.int16). I can't actually say what the problem is and I really hope someone can help. Thank you in advance !

  


  EDIT
This is the django view for retrieving the waveform data :

  


  NB : I've only included useful codes as I'm typing with my mobile phone.

  


  def waveform(self, request, ptype, id):
    project = Project.objects.get(pk=id)
    audio = project.audio

    mp3_path = os.path.join(cdn_dir, audio) 
    cmd = ['ffmpeg', '-i', mp3_path, '-f', 'wav', '-']
    p = Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE, creationflags=0x8000000)
    data = p.communicate()[0]
    array = np.fromstring(data[data.find("data")+4:], np.int16)

    return Response(array)


  


  The TypeError I get is this :
TypeError: argument should be integer or bytes-like object, not "str"

  


• Curator of the Samples Archive

  13 mai 2011, par Multimedia Mike — General

  Remember how I mirrored the world-famous MPlayerHQ samples archive a few months ago ? Due to a series of events, the original archive is no longer online. However, me and the people who control the mplayerhq.hu domain figured out how to make samples.mplayerhq.hu point to samples.multimedia.cx.

  That means... I’m the current owner and curator of our central multimedia samples repository. Such power ! This should probably be the fulfillment of a decade-long dream for me, having managed swaths of the archive, most notably the game formats section.

  How This Came To Be

  If you pay any attention to the open source multimedia scene, you might have noticed that there has been a smidge of turmoil. Heated words were exchanged, authority was questioned, some people probably said some things they didn’t mean, and the upshot is that, where once there was one project (FFmpeg), there are now 2 projects (also Libav). And to everyone who has wanted me to mention it on my blog— there, I finally broke my silence and formally acknowledged the schism.

  For my part, I was just determined to ensure that the samples archive remained online, preferably at the original samples.mplayerhq.hu address. There are 10 years worth of web links out there pointing into the original repository.

  Better Solution

  I concede that it’s not entirely optimal to host the repository here at multimedia.cx. While I can offer a crazy amount of monthly bandwidth, I can’t offer rsync (invaluable for keeping mirrors in sync), nor can the server provide anonymous FTP or allow me to offer accounts to other admins who can manage the repository.

  The samples archive is also mirrored at samples.libav.org/samples. I understand that service is provided by VideoLAN. Right now, both repositories are known to be static. I’m open to brainstorms about how to improve the situation.

• FFmpeg cant recognize 3 channels with each 32 bit

  4 avril 2022, par Chryfi

  I am writing the linearized depth buffer of a game to openEXR using FFmpeg. Unfortunately, FFmpeg does not adhere to the openEXR file specification fully (like allowing unsigned integer for one channel) so I am writing one float channel to openEXR, which is put into the green channel with this command -f rawvideo -pix_fmt grayf32be -s %WIDTH%x%HEIGHT% -r %FPS% -i - -vf %DEFVF% -preset ultrafast -tune zerolatency -qp 6 -compression zip1 -pix_fmt gbrpf32le %NAME%_depth_%d.exr.

  


  The float range is from 0F to 1F and it is linear. I can confirm that the calculation and linearization is correct by testing 16 bit integer (per pixel component) PNG in Blender compositor. The 16 bit integer data is written like this short s = (short) (linearzieDepth(depth) * (Math.pow(2,16) - 1)) whereas for float the linearized value is directly written to OpenEXR without multiplying with a value.

  


  However, when viewing the openEXR file it doesn't have the same "gradient" as the 16 bit png... when viewing them side by side, it appears as if the values near 0 are not linear, and they are not as dark as they should be like in the 16 bit png.
(And yes, I set the image node to linear), and comparing it with 3d tracking data from the game I cant reproduce the depth and cant mask things using the depth buffer where as with the png I can.

  


  How is it possible for a linear float range to turn out so different to a linear integer range in an image ?

  


  UPDATE :

  


  I now write 3 channels to the ffmpeg with this code

  


  float f2 = this.linearizeDepth(depth);

buffer.putFloat(f2);
buffer.putFloat(0);
buffer.putFloat(0);


  


  the byte buffer is of the size width * height * 3 * 4 -> 3 channels with each 4 bytes. The command is now -f rawvideo -pix_fmt gbrpf32be -s %WIDTH%x%HEIGHT% -r %FPS% -i - -vf %DEFVF% -preset ultrafast -tune zerolatency -qp 6 -compression zip1 -pix_fmt gbrpf32le %NAME%_depth_%d.exr which should mean that the input (byte buffer) is expecting 32 bit floats with 3 channels.

  


  FFmpeg is somehow splitting up channels or whatever... could be a bug, could be my fault ?