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• FFmpeg save .mp3 output into a variable

  6 mai 2021, par Toto Briac

  In my application I want to modify various mp3 and then mix them together. I know I could do it with a single command line in FFmpeg but It can end up very messy since I need to use various filter on each sample and I have five of them.
My idea is to edit each sample individually, save them into a variable and finally mix them. This is my code :

  


  import subprocess    

def create_samp():
    sample= subprocess.run(["ffmpeg", "-y", "-i", "https://freesound.org/data/previews/186/186942_2594536-hq.mp3", \
                           "-filter_complex", "adelay=15000|15000", "-codec:v", "copy", "-f", "mp3","-"], stdout=subprocess.PIPE)         
    return(sample)    

def record(samp):
    subprocess.run(["ffmpeg", "-y", "-i", "https://cdns-preview-b.dzcdn.net/stream/c-b0b684fe962f93dc43f1f7ea493683a1-3.mp3", \
                    "-i", samp.stdout, "-f", "-mp3", "copy", "output.mp3"])

samp = create_samp()
record(samp)


  


  My issue is that I have to encode the stdout. I've tried 'utf-8' but got this error :

  


  UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 45: invalid start byte


  


  With `'utf-16' :

  


  UnicodeDecodeError: 'utf-16-le' codec can't decode bytes in position 239454-239455: illegal encoding


  


  Why is the way to fix this issue ? Is my approach the right one ?

  


  Thanks to @Rotem I succeed to do what I wanted to. But now I am facing an other issue, since I want to mix up to 5 sounds, I tried to implement it the lazy/easy way :

  


  import subprocess

def create_samp_2():
    sample= subprocess.run(["ffmpeg", "-i", "https://freesound.org/data/previews/186/186942_2594536-hq.mp3", \
                            "-af", "adelay=15000|15000", "-f", "mp3", "pipe:"], stdout=subprocess.PIPE).stdout
    return(sample)

def create_samp():

    sample= subprocess.run(["ffmpeg", "-i", "https://freesound.org/data/previews/370/370934_6399962-lq.ogg", \
                            "-af", "adelay=1000|1000", "-f", "mp3", "pipe:"], stdout=subprocess.PIPE).stdout
    return(sample)


def record(samp, samp_2):        
    process = subprocess.Popen(["ffmpeg", "-y", '-f', 'mp3', \
                                "-i", "https://cdns-preview-b.dzcdn.net/stream/c-b0b684fe962f93dc43f1f7ea493683a1-3.mp3", \
                                "-i", "pipe:", \
                                "-i", "pipe:", \
                                "-filter_complex", "amix=inputs=3:duration=longest", "output.mp3"], stdin=subprocess.PIPE)

    process.stdin.write(samp) 
    process.stdin.write(samp_2)        
    process.stdin.close()  
    process.wait()

samp = create_samp()
samp_2 = create_samp_2()
record(samp, samp_2)


  


  Surprisingly it works, my two sounds start at the right time, but the second sound is messed up. So it's not the right way to do it.

  


  Then I tried named pipes as suggested this way :

  


  "pipe1:"


  


  But I get this error :

  


  pipe1:: Protocol not found
Did you mean file:pipe1:?


  


  Reading named pipe wiki it is stated that I have to create them with mkfifo().

  


  So I tried :

  


  import os
pipe1 = "pipe1"

def create_pipe1():
    os.mkfifo(pipe1)

But now I have this error: pipe1:: Protocol not found
Did you mean file:pipe1:?


  


• avcodec/speedhqenc : Hardcode table to save space

  10 décembre 2020, par Andreas Rheinhardt

  avcodec/speedhqenc : Hardcode table to save space
  The SpeedHQ encoder currently reverses the entries of two small tables
  
  and stores them in other tables. These other tables have a size of 48
  
  bytes, yet the code for their initialization takes 135 bytes (GCC 9.3,
  
  x64, O3 albeit in an av_cold function). So remove the runtime
  
  initialization and hardcode the tables.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/speedhqenc.c

• avcodec/mqc : Hardcode tables to save space

  7 mai 2021, par Andreas Rheinhardt

  avcodec/mqc : Hardcode tables to save space
  mqc currently initializes three arrays at runtime ; each of them
  
  has 2 * 47 elements, one is uint16_t, two are uint8_t, so that their
  
  combined size is 8 * 47. The source data for these initializations
  
  is contained in an array of 47 elements of size six. Said array is
  
  only used in order to initialize the other arrays, so the savings
  
  are just 2 * 47B. Yet this is dwarfed by the size of the code for
  
  performing the initializations : It is 109B (GCC 10.2, x64, -O3 albeit
  
  in an av_cold function) ; this does not even include the size of the
  
  code in the callers. So just hardcode these tables.
  This also fixes a data race, because the encoder always initialized
  
  these tables during init, although they might already be used at the
  
  same time by already running encoder/decoder instances.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/j2kenc.c
  • [DH] libavcodec/jpeg2000dec.c
  • [DH] libavcodec/mqc.c
  • [DH] libavcodec/mqc.h