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• swscale : fix gbrap16 alpha channel issues

  3 août 2017, par James Cowgill

  swscale : fix gbrap16 alpha channel issues
  Fixes filter-pixfmts-scale test failing on big-endian systems due to
  
  alpSrc not being cast to (const int32_t**).
  Also fixes distortions in the output alpha channel values by copying the
  
  alpha channel code from the rgba64 case found elsewhere in output.c.
  Fixes ticket 6555.
  Signed-off-by : James Cowgill <James.Cowgill@imgtec.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libswscale/output.c
  • [DH] tests/ref/fate/filter-pixfmts-scale

• Python : How to decode a mp3 chunk into PCM samples ?

  30 mars 2021, par Bendzko

  I'm trying to catch chunks of an mp3 webstream and decoding them into PCM samples for signal processing. I tried to catch the audio via requests and io.BytesIO to save the data as .wav file.

  



  I have to convert the mp3 data to wav data, but I don't know how. (My goal is not to record a .wav file, i am just doing this to test the algorithm.)

  



  I found the pymedia lib, but it is very old (last commit in 2006), using python 2.7 and for me not installable.

  



  Maybe it is possible with ffmpeg-python, but I have just seen examples using files as input and output.

  



  Here's my code :

  



  import requests
import io
import soundfile as sf
import struct
import wave
import numpy as np


def main():
    stream_url = r'http://dg-wdr-http-dus-dtag-cdn.cast.addradio.de/wdr/1live/diggi/mp3/128/stream.mp3'
    r = requests.get(stream_url, stream=True)
    sample_array = []
    try:
        for block in r.iter_content(1024):
            data, samplerate = sf.read(io.BytesIO(block), format="RAW", channels=2, samplerate=44100, subtype='FLOAT',
                                       dtype='float32')
            sample_array = np.append(sample_array, data)

    except KeyboardInterrupt:
        print("...saving")
        obj = wave.open('sounds/stream1.wav', 'w')
        obj.setnchannels(1)  # mono
        obj.setsampwidth(2)  # bytes
        obj.setframerate(44100)

        data_max = np.nanmax(abs(sample_array))

        # fill WAV with samples from sample_array
        for sample in sample_array:
            if (np.isnan(sample) or np.isnan(32760 * sample / data_max)) is True:
                continue
            try:
                value = int(32760 * sample / data_max)  # normalization INT16
            except ValueError:
                value = 1
            finally:
                data = struct.pack('code>

  



  Do you have an idea how to handle this problem ?

  


• avutil/libm : correct isnan, isinf compat hacks

  15 novembre 2015, par Ganesh Ajjanagadde

  avutil/libm : correct isnan, isinf compat hacks
  isnan and isinf are actually macros as per the standard. In particular,
  
  the existing implementation has incorrect signature. Furthermore, this
  
  results in undefined behavior for e.g double values outside float range
  
  as per the standard.
  This patch corrects the undefined behavior for all usage within FFmpeg.
  Note that long double is not handled as it is not used in FFmpeg.
  
  Furthermore, even if at some point long double gets used, it is likely
  
  not needed to modify the macro in practice for usage in FFmpeg. See
  
  below for analysis.
  Getting long double to work strictly per the spec is significantly harder
  
  since a long double may be an IEEE 128 bit quad (very rare), 80 bit
  
  extended precision value (on GCC/Clang), or simply double (on recent Microsoft).
  
  On the other hand, any potential future usage of long double is likely
  
  for precision (when a platform offers extra precision) and not for range, since
  
  the range anyway varies and is not as portable as IEEE 754 single/double
  
  precision. In such cases, the implicit cast to a double is well defined
  
  and isinf and isnan should work as intended.
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Signed-off-by : Ganesh Ajjanagadde <gajjanagadde@gmail.com>
  

  • [DH] libavutil/libm.h