Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
420 views
in Technique[技术] by (71.8m points)

python - Trying to simulate constant byte rate. Confusion with time.sleep results

Context

I'm using windows 7 on my computer(the player) and linux(debian) on my college computer(the streamer), which I control using ssh.
I was trying to simulate a constant byte rate of a microphone from reading a wave file, as if someone was talking. The problem was that the byte rate was below the target.

Choosing a 32KB/s rate, and 0.020 seconds of capture time.
I implemented the simulated microphone using time.sleep to produce give each chunk of data each 0.020 seconds. But the rate obtained was around 27KB/s, not 32KB/s

The problem

I decided to test how much precise time.sleep was on the linux machine, using ideas by reading this question.

I did 2 kind of tests. 1) busy sleep 2) normal sleep

In average, from the samples I got, it shows that the linux machine sleep resolution is 4ms. While on windows its less/equal to 1ms.

Questions

  1. What can possibly be limiting the sleep resolution on the linux machine?
  2. (On linux) Why does busy sleeping has the same resolution as time.sleep?
  3. How could I successfully simulate a microphone from reading a wave file?

Code

import time

def busy_sleep(t):
    s=time.time()
    while time.time() - s < t:
        pass
    e=time.time()
    return e-s

def normal_sleep(t):
    s=time.time()
    time.sleep(t)
    e=time.time()
    return e-s

def test(fun):
    f = lambda x: sum(fun(x) for d in range(10))/10
    print("0.100:{}".format(f(0.100)))
    print("0.050:{}".format(f(0.050)))
    print("0.025:{}".format(f(0.025)))
    print("0.010:{}".format(f(0.010)))
    print("0.009:{}".format(f(0.010)))
    print("0.008:{}".format(f(0.008)))
    print("0.007:{}".format(f(0.007)))
    print("0.006:{}".format(f(0.006)))
    print("0.005:{}".format(f(0.005)))
    print("0.004:{}".format(f(0.004)))
    print("0.003:{}".format(f(0.003)))
    print("0.002:{}".format(f(0.002)))
    print("0.001:{}".format(f(0.001)))

if __name__=="__main__":
    print("Testing busy_sleep:")
    test(busy_sleep)
    print("Testing normal_sleep:")
    test(normal_sleep)

Results

"""
Debian
Testing busy_sleep:
0.100:0.10223722934722901
0.050:0.051996989250183104
0.025:0.027996940612792967
0.020:0.02207831859588623
0.010:0.011997451782226562
0.009:0.011997222900390625
0.008:0.009998440742492676
0.007:0.007997279167175292
0.006:0.0079974365234375
0.005:0.007997465133666993
0.004:0.005918483734130859
0.003:0.003997836112976074
0.002:0.0039977550506591795
0.001:0.003997611999511719
Testing normal_sleep:
0.100:0.1020797061920166
0.050:0.051999988555908205
0.025:0.028000001907348634
0.020:0.02192000865936279
0.010:0.011999979019165039
0.009:0.012000055313110351
0.008:0.010639991760253906
0.007:0.008000001907348633
0.006:0.00799997329711914
0.005:0.008000059127807617
0.004:0.006159958839416504
0.003:0.004000000953674317
0.002:0.00399998664855957
0.001:0.004000091552734375

$ uname -a
Linux 3.2.0-4-amd64 #1 SMP Debian 3.2.57-3+deb7u2 x86_64 GNU/Linux
"""

"""
Windows 7

Testing busy_sleep:
0.100:0.10000572204589844
0.050:0.05000288486480713
0.025:0.0250014066696167
0.010:0.010500597953796388
0.009:0.010500597953796388
0.008:0.008000493049621582
0.007:0.00740041732788086
0.006:0.006400299072265625
0.005:0.005400300025939942
0.004:0.004700303077697754
0.003:0.003200197219848633
0.002:0.002700185775756836
0.001:0.0016000032424926759
Testing normal_sleep:
0.100:0.10000579357147217
0.050:0.0500028133392334
0.025:0.02500150203704834
0.010:0.01000049114227295
0.009:0.0100006103515625
0.008:0.008000493049621582
0.007:0.007000398635864257
0.006:0.006000304222106934
0.005:0.00500030517578125
0.004:0.0040001869201660155
0.003:0.0030002117156982424
0.002:0.0020000934600830078
0.001:0.0010000944137573243
"""

Real code

import os import wave import sys import io import time

FORMAT = 8 #get_format_from_width(2)
NCHANNELS = 1
FRAMERATE = 16000 # samples per second
SAMPWIDTH = 2 # bytes in a sample
BYTE_RATE = FRAMERATE*SAMPWIDTH
CHUNK_DURATION = 0.020
CHUNK_BYTES = int(CHUNK_DURATION*BYTE_RATE)

class StreamSimulator:
    def __init__(self):
        wf = wave.open("Kalimba.wav","rb")
        buf = io.BytesIO()
        buf.write(wf.readframes(wf.getnframes()))
        wf.close()
        buf.seek(0)
        self.buf = buf
        self.step = time.time()

    def delay(self):
        #delay
        delta = time.time() - self.step 
        self.step=time.time()
        delay = CHUNK_DURATION - delta      
        if delay > 0.001:
            time.sleep(delay)


    def read(self):
        buf = self.buf  
        data = buf.read(CHUNK_BYTES)
        if len(data) == 0:
            buf.seek(0)
            data = buf.read(CHUNK_BYTES)

        self.delay()
        return data

    def close(self):
        self.buf.close()

class DynamicPainter:
    def __init__(self):
        self.l=0

    def paint(self,obj):        
        str1=str(obj)
        l1=len(str1)
        bs=""*self.l
        clean=" "*self.l
        total = bs+clean+bs+str1
        sys.stdout.write(total)
        sys.stdout.flush()
        self.l=l1

if __name__=="__main__":
    painter = DynamicPainter()
    stream = StreamSimulator()
    produced = 0
    how_many = 0
    painted = time.time()
    while True:
        while time.time()-painted < 1:
            d = stream.read()
            produced += len(d)
            how_many += 1
        producing_speed = int(produced/(time.time()-painted))       
        painter.paint("Producing speed: {} how many: {}".format(producing_speed,how_many))
        produced=0
        how_many=0
        painted = time.time()

Edit

Changed "Real Code" , added measure of time including sleeping time.
But now I have the DOUBLE Byte Rate: Producing speed: 63996 how many: 100
This got me so MUCH confused. I have tried with different byterates and it ends up being the double everytime.

Conclusion

Thanks to @J.F.Sebastian and his code, I came to learned that:

  • Its better to use use a deadline as a time reference than create to a new reference each loop
  • Using a deadline "amortizes" the imprecision of time.sleep, oscilating a bit around the desired bitrate but resulting in an correct(and much more constant) average.
  • You only need to you use time.time() once, that means less calculations imprecisions.

As a result, I get a constant 32000 B/s some times oscilating to 31999 and very rarely to 31745
Now I can hear the music without any lag or jitter!

Final Code

def read(self):
    buf = self.buf  
    data = buf.read(CHUNK_BYTES)
    if len(data) == 0:
        buf.seek(0)
        data = buf.read(CHUNK_BYTES)

    self.deadline += CHUNK_DURATION 
    delay = self.deadline - time.time()
    if delay > 0:
        time.sleep(delay)
    return data
See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

Conclusion

Thanks to @J.F.Sebastian and his code, I came to learned that:

  • Its better to use use a deadline as a time reference than create to a new reference each loop
  • Using a deadline "amortizes" the imprecision of time.sleep, oscilating a bit around the desired bitrate but resulting in an correct(and much more constant) average.
  • You only need to you use time.time() once, that means less calculations imprecisions.

As a result, I get a constant 32000 B/s some times oscilating to 31999 and very rarely to 31745
Now I can hear the music without any lag or jitter!

I tried using @J.F.Sebastian implentation using only the % operator to sleep the remainder, but the KB/s oscilate strangelly, so I decided to keep the deadline implementation, which suffers imprecision by keeping adding a float value. Nevertheless, the overall result is enough for my needs.
Thank you everyone.

Final Code

def read(self):
    self.deadline += 0.020  
    delay = self.deadline - time.perf_counter()
    if delay > 0:
        time.sleep(delay)
    return self._read()

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...