In [64]:
from IPython.display import Image
Image('meowing-original-spectrogram.png')
Out[64]:
Transcoding is the conversion of one digital data format into another digital format. Most of the time, transcoding is an attempt to convert the source material into a smaller material by means of compression. Transcodology is the science that observes and analyses the different actors involved in transcoding. A sub-discipline of transcodology is compressology. Anyway, lets have a look into the world of transcoding.
For our experiment today, we need a high-quality source material. Therefore, we are now looking for a good cat meow in the freesound library. freesound is a community-run sound library with more than 500k Creative Commons sounds. Because of the licence used in the freesound library, we don't have to worry about copyright infringements in this transcolodgy exercise *wink smiley*
Alright, the cat meowing uploaded by the user nekoninja in very good quality (wav-format, samplerate 44100.0 Hz, bitdepth 16 bit, channels stereo) is our selected source material. The user nekoninja mentions in the description that the cats name is sushi. Thank you sushi and nekoninja!
Lets see what info we can get about the file (called "cat-meowing-original.wav" with the following command:
! ffprobe -hide_banner cat-meowing-original.wav
Input #0, wav, from 'cat-meowing-original.wav':
Metadata:
encoder : Coderium SoundEngine 5.21
Duration: 00:00:10.18, bitrate: 1411 kb/s
Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, 2 channels, s16, 1411 kb/s
And we listen to the sound file with the following command:
from IPython.display import Audio
Audio('cat-meowing-original.wav', autoplay=True)
Now we are going to create a spectogram of the file with the following ffmpeg-command:
! ffmpeg -hide_banner -i cat-meowing-original.wav -lavfi showspectrumpic=s=1000x400:mode=separate meowing-original-spectrogram.png -y
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, wav, from 'cat-meowing-original.wav':
Metadata:
encoder : Coderium SoundEngine 5.21
Duration: 00:00:10.18, bitrate: 1411 kb/s
Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
Stream mapping:
Stream #0:0 (pcm_s16le) -> showspectrumpic
showspectrumpic -> Stream #0:0 (png)
Press [q] to stop, [?] for help
Output #0, image2, to 'meowing-original-spectrogram.png':
Metadata:
encoder : Lavf58.20.100
Stream #0:0: Video: png, rgb24, 1282x528 [SAR 1:1 DAR 641:264], q=2-31, 200 kb/s, 86.13 fps, 86.13 tbn, 86.13 tbc
Metadata:
encoder : Lavc58.35.100 png
frame= 1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.01 bitrate=N/A speed=0.0167x
video:580kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
from IPython.display import Image
Image('meowing-original-spectrogram.png')
In the next to steps we will transcode the original wav-file to a high quality mp3-file and a low quality mp3-file!
First the compression into a high quality mp3-file with 128kbps:
! ffmpeg -hide_banner -i cat-meowing-original.wav -b:a 128k cat-meowing-128k.mp3 -y
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, wav, from 'cat-meowing-original.wav':
Metadata:
encoder : Coderium SoundEngine 5.21
Duration: 00:00:10.18, bitrate: 1411 kb/s
Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (pcm_s16le (native) -> mp3 (libmp3lame))
Press [q] to stop, [?] for help
Output #0, mp3, to 'cat-meowing-128k.mp3':
Metadata:
TSSE : Lavf58.20.100
Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, stereo, s16p, 128 kb/s
Metadata:
encoder : Lavc58.35.100 libmp3lame
size= 160kB time=00:00:10.18 bitrate= 128.7kbits/s speed=19.9x
video:0kB audio:160kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.282704%
from IPython.display import Audio
Audio('cat-meowing-128k.mp3', autoplay=True)
And now the spectogram of it:
! ffmpeg -hide_banner -i cat-meowing-128k.mp3 -lavfi showspectrumpic=s=1000x400:mode=separate:legend=disabled meowing-128k-spectrogram.png -y
Input #0, mp3, from 'cat-meowing-128k.mp3':
Metadata:
encoder : Lavf58.20.100
Duration: 00:00:10.21, start: 0.025057, bitrate: 128 kb/s
Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 128 kb/s
Metadata:
encoder : Lavc58.35
Stream mapping:
Stream #0:0 (mp3float) -> showspectrumpic
showspectrumpic -> Stream #0:0 (png)
Press [q] to stop, [?] for help
Output #0, image2, to 'meowing-128k-spectrogram.png':
Metadata:
encoder : Lavf58.20.100
Stream #0:0: Video: png, rgb24, 1000x400 [SAR 1:1 DAR 5:2], q=2-31, 200 kb/s, 86.13 fps, 86.13 tbn, 86.13 tbc
Metadata:
encoder : Lavc58.35.100 png
frame= 1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.01 bitrate=N/A speed=0.016x
video:544kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
from IPython.display import Image
Image('meowing-128k-spectrogram.png')
Lets make a really low compression of the original file:
! ffmpeg -hide_banner -i cat-meowing-original.wav -b:a 8k cat-meowing-8k.mp3 -y
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, wav, from 'cat-meowing-original.wav':
Metadata:
encoder : Coderium SoundEngine 5.21
Duration: 00:00:10.18, bitrate: 1411 kb/s
Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (pcm_s16le (native) -> mp3 (libmp3lame))
Press [q] to stop, [?] for help
Output #0, mp3, to 'cat-meowing-8k.mp3':
Metadata:
TSSE : Lavf58.20.100
Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, stereo, s16p, 8 kb/s
Metadata:
encoder : Lavc58.35.100 libmp3lame
size= 40kB time=00:00:10.18 bitrate= 32.3kbits/s speed=22.2x
video:0kB audio:40kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.619248%
! ffmpeg -hide_banner -i cat-meowing-8k.mp3 -lavfi showspectrumpic=s=1000x400:mode=separate:legend=disabled meowing-8k-spectrogram.png -y
Input #0, mp3, from 'cat-meowing-8k.mp3':
Metadata:
encoder : Lavf58.20.100
Duration: 00:00:10.21, start: 0.025057, bitrate: 32 kb/s
Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 32 kb/s
Metadata:
encoder : Lavc58.35
Stream mapping:
Stream #0:0 (mp3float) -> showspectrumpic
showspectrumpic -> Stream #0:0 (png)
Press [q] to stop, [?] for help
Output #0, image2, to 'meowing-8k-spectrogram.png':
Metadata:
encoder : Lavf58.20.100
Stream #0:0: Video: png, rgb24, 1000x400 [SAR 1:1 DAR 5:2], q=2-31, 200 kb/s, 86.13 fps, 86.13 tbn, 86.13 tbc
Metadata:
encoder : Lavc58.35.100 png
frame= 1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.01 bitrate=N/A speed=0.0313x
video:113kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
from IPython.display import Image
Image('meowing-8k-spectrogram.png')
from IPython.display import Audio
Audio('cat-meowing-8k.mp3', autoplay=True)
What we can see from the image and hear from the audio is that the mp3 compression cuts already a lot of the high frequenies! Lets compare the file sizes of the three different files:
! ls -al *.wav *.mp3
-rw-rw-r--+ 1 joak joak 163675 Apr 19 07:45 cat-meowing-128k.mp3 -rw-rw-r--+ 1 joak joak 41109 Apr 19 08:06 cat-meowing-8k.mp3 -rw-rw-r--+ 1 joak joak 1796250 Apr 18 23:00 cat-meowing-original.wav
In the next step we will transcode the 'cat-meowing-128k.mp3'-file 100 times and listen what kind of glitches will appear :D
import os
os.system("cp -f cat-meowing-128k.mp3 test/0.mp3") #copy the mp3 to the test folder
for i in range(0,100):
os.system("ffmpeg -loglevel quiet -hide_banner -i test/"+str(i)+".mp3 test/"+str(i)+".wav -y") #convert from mp3 to wav
os.system("ffmpeg -loglevel quiet -hide_banner -i test/"+str(i)+".wav -b:a 32k -filter:a 'volume=1.05' test/"+str(i+1)+".mp3 -y") #convert from wav to mp3
print("Now the script is at step "+str(i)+" of 99")
print("Finished")
Now the script is at step 0 of 99 Now the script is at step 1 of 99 Now the script is at step 2 of 99 Now the script is at step 3 of 99 Now the script is at step 4 of 99 Now the script is at step 5 of 99 Now the script is at step 6 of 99 Now the script is at step 7 of 99 Now the script is at step 8 of 99 Now the script is at step 9 of 99 Now the script is at step 10 of 99 Now the script is at step 11 of 99 Now the script is at step 12 of 99 Now the script is at step 13 of 99 Now the script is at step 14 of 99 Now the script is at step 15 of 99 Now the script is at step 16 of 99 Now the script is at step 17 of 99 Now the script is at step 18 of 99 Now the script is at step 19 of 99 Now the script is at step 20 of 99 Now the script is at step 21 of 99 Now the script is at step 22 of 99 Now the script is at step 23 of 99 Now the script is at step 24 of 99 Now the script is at step 25 of 99 Now the script is at step 26 of 99 Now the script is at step 27 of 99 Now the script is at step 28 of 99 Now the script is at step 29 of 99 Now the script is at step 30 of 99 Now the script is at step 31 of 99 Now the script is at step 32 of 99 Now the script is at step 33 of 99 Now the script is at step 34 of 99 Now the script is at step 35 of 99 Now the script is at step 36 of 99 Now the script is at step 37 of 99 Now the script is at step 38 of 99 Now the script is at step 39 of 99 Now the script is at step 40 of 99 Now the script is at step 41 of 99 Now the script is at step 42 of 99 Now the script is at step 43 of 99 Now the script is at step 44 of 99 Now the script is at step 45 of 99 Now the script is at step 46 of 99 Now the script is at step 47 of 99 Now the script is at step 48 of 99 Now the script is at step 49 of 99 Now the script is at step 50 of 99 Now the script is at step 51 of 99 Now the script is at step 52 of 99 Now the script is at step 53 of 99 Now the script is at step 54 of 99 Now the script is at step 55 of 99 Now the script is at step 56 of 99 Now the script is at step 57 of 99 Now the script is at step 58 of 99 Now the script is at step 59 of 99 Now the script is at step 60 of 99 Now the script is at step 61 of 99 Now the script is at step 62 of 99 Now the script is at step 63 of 99 Now the script is at step 64 of 99 Now the script is at step 65 of 99 Now the script is at step 66 of 99 Now the script is at step 67 of 99 Now the script is at step 68 of 99 Now the script is at step 69 of 99 Now the script is at step 70 of 99 Now the script is at step 71 of 99 Now the script is at step 72 of 99 Now the script is at step 73 of 99 Now the script is at step 74 of 99 Now the script is at step 75 of 99 Now the script is at step 76 of 99 Now the script is at step 77 of 99 Now the script is at step 78 of 99 Now the script is at step 79 of 99 Now the script is at step 80 of 99 Now the script is at step 81 of 99 Now the script is at step 82 of 99 Now the script is at step 83 of 99 Now the script is at step 84 of 99 Now the script is at step 85 of 99 Now the script is at step 86 of 99 Now the script is at step 87 of 99 Now the script is at step 88 of 99 Now the script is at step 89 of 99 Now the script is at step 90 of 99 Now the script is at step 91 of 99 Now the script is at step 92 of 99 Now the script is at step 93 of 99 Now the script is at step 94 of 99 Now the script is at step 95 of 99 Now the script is at step 96 of 99 Now the script is at step 97 of 99 Now the script is at step 98 of 99 Now the script is at step 99 of 99 Finished
from IPython.display import Audio
Audio('test/100.mp3', autoplay=True)
! ffmpeg -hide_banner -i test/100.mp3 -lavfi showspectrumpic=s=1000x400:mode=separate:legend=disabled test/meowing-100times-spectrogram.png -y
Input #0, mp3, from 'test/100.mp3':
Metadata:
encoder : Lavf58.20.100
Duration: 00:00:10.21, start: 0.025057, bitrate: 32 kb/s
Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 32 kb/s
Metadata:
encoder : Lavc58.35
Stream mapping:
Stream #0:0 (mp3float) -> showspectrumpic
showspectrumpic -> Stream #0:0 (png)
Press [q] to stop, [?] for help
Output #0, image2, to 'test/meowing-100times-spectrogram.png':
Metadata:
encoder : Lavf58.20.100
Stream #0:0: Video: png, rgb24, 1000x400 [SAR 1:1 DAR 5:2], q=2-31, 200 kb/s, 86.13 fps, 86.13 tbn, 86.13 tbc
Metadata:
encoder : Lavc58.35.100 png
frame= 1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.01 bitrate=N/A speed=0.0272x
video:186kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
from IPython.display import Image
Image('test/meowing-100times-spectrogram.png')
Alright that goes into a good direction and even the spectogram looks good. Lets trey it now with 400 times :D
import os
os.system("cp -f cat-meowing-128k.mp3 test/0.mp3") #copy the mp3 to the test folder
for i in range(0,400):
os.system("ffmpeg -loglevel quiet -hide_banner -i test/"+str(i)+".mp3 test/"+str(i)+".wav -y") #convert from mp3 to wav
os.system("ffmpeg -loglevel quiet -hide_banner -i test/"+str(i)+".wav -b:a 32k -filter:a 'volume=1.05' test/"+str(i+1)+".mp3 -y") #convert from wav to mp3
print("Now the script is at step "+str(i)+" of 399")
print("Finished")
Now the script is at step 0 of 399 Now the script is at step 1 of 399 Now the script is at step 2 of 399 Now the script is at step 3 of 399 Now the script is at step 4 of 399 Now the script is at step 5 of 399 Now the script is at step 6 of 399 Now the script is at step 7 of 399 Now the script is at step 8 of 399 Now the script is at step 9 of 399 Now the script is at step 10 of 399 Now the script is at step 11 of 399 Now the script is at step 12 of 399 Now the script is at step 13 of 399 Now the script is at step 14 of 399 Now the script is at step 15 of 399 Now the script is at step 16 of 399 Now the script is at step 17 of 399 Now the script is at step 18 of 399 Now the script is at step 19 of 399 Now the script is at step 20 of 399 Now the script is at step 21 of 399 Now the script is at step 22 of 399 Now the script is at step 23 of 399 Now the script is at step 24 of 399 Now the script is at step 25 of 399 Now the script is at step 26 of 399 Now the script is at step 27 of 399 Now the script is at step 28 of 399 Now the script is at step 29 of 399 Now the script is at step 30 of 399 Now the script is at step 31 of 399 Now the script is at step 32 of 399 Now the script is at step 33 of 399 Now the script is at step 34 of 399 Now the script is at step 35 of 399 Now the script is at step 36 of 399 Now the script is at step 37 of 399 Now the script is at step 38 of 399 Now the script is at step 39 of 399 Now the script is at step 40 of 399 Now the script is at step 41 of 399 Now the script is at step 42 of 399 Now the script is at step 43 of 399 Now the script is at step 44 of 399 Now the script is at step 45 of 399 Now the script is at step 46 of 399 Now the script is at step 47 of 399 Now the script is at step 48 of 399 Now the script is at step 49 of 399 Now the script is at step 50 of 399 Now the script is at step 51 of 399 Now the script is at step 52 of 399 Now the script is at step 53 of 399 Now the script is at step 54 of 399 Now the script is at step 55 of 399 Now the script is at step 56 of 399 Now the script is at step 57 of 399 Now the script is at step 58 of 399 Now the script is at step 59 of 399 Now the script is at step 60 of 399 Now the script is at step 61 of 399 Now the script is at step 62 of 399 Now the script is at step 63 of 399 Now the script is at step 64 of 399 Now the script is at step 65 of 399 Now the script is at step 66 of 399 Now the script is at step 67 of 399 Now the script is at step 68 of 399 Now the script is at step 69 of 399 Now the script is at step 70 of 399 Now the script is at step 71 of 399 Now the script is at step 72 of 399 Now the script is at step 73 of 399 Now the script is at step 74 of 399 Now the script is at step 75 of 399 Now the script is at step 76 of 399 Now the script is at step 77 of 399 Now the script is at step 78 of 399 Now the script is at step 79 of 399 Now the script is at step 80 of 399 Now the script is at step 81 of 399 Now the script is at step 82 of 399 Now the script is at 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Now the script is at step 327 of 399 Now the script is at step 328 of 399 Now the script is at step 329 of 399 Now the script is at step 330 of 399 Now the script is at step 331 of 399 Now the script is at step 332 of 399 Now the script is at step 333 of 399 Now the script is at step 334 of 399 Now the script is at step 335 of 399 Now the script is at step 336 of 399 Now the script is at step 337 of 399 Now the script is at step 338 of 399 Now the script is at step 339 of 399 Now the script is at step 340 of 399 Now the script is at step 341 of 399 Now the script is at step 342 of 399 Now the script is at step 343 of 399 Now the script is at step 344 of 399 Now the script is at step 345 of 399 Now the script is at step 346 of 399 Now the script is at step 347 of 399 Now the script is at step 348 of 399 Now the script is at step 349 of 399 Now the script is at step 350 of 399 Now the script is at step 351 of 399 Now the script is at step 352 of 399 Now the script is at step 353 of 399 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Now the script is at step 381 of 399 Now the script is at step 382 of 399 Now the script is at step 383 of 399 Now the script is at step 384 of 399 Now the script is at step 385 of 399 Now the script is at step 386 of 399 Now the script is at step 387 of 399 Now the script is at step 388 of 399 Now the script is at step 389 of 399 Now the script is at step 390 of 399 Now the script is at step 391 of 399 Now the script is at step 392 of 399 Now the script is at step 393 of 399 Now the script is at step 394 of 399 Now the script is at step 395 of 399 Now the script is at step 396 of 399 Now the script is at step 397 of 399 Now the script is at step 398 of 399 Now the script is at step 399 of 399 Finished
! ffmpeg -hide_banner -i test/400.mp3 -lavfi showspectrumpic=s=1000x400:mode=separate:legend=disabled test/meowing-400times-spectrogram.png -y
Input #0, mp3, from 'test/400.mp3':
Metadata:
encoder : Lavf58.20.100
Duration: 00:00:10.21, start: 0.025057, bitrate: 32 kb/s
Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 32 kb/s
Metadata:
encoder : Lavc58.35
Stream mapping:
Stream #0:0 (mp3float) -> showspectrumpic
showspectrumpic -> Stream #0:0 (png)
Press [q] to stop, [?] for help
Output #0, image2, to 'test/meowing-400times-spectrogram.png':
Metadata:
encoder : Lavf58.20.100
Stream #0:0: Video: png, rgb24, 1282x528 [SAR 1:1 DAR 641:264], q=2-31, 200 kb/s, 86.13 fps, 86.13 tbn, 86.13 tbc
Metadata:
encoder : Lavc58.35.100 png
frame= 1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.01 bitrate=N/A speed=0.026x
video:196kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
from IPython.display import Image
Image('test/meowing-400times-spectrogram.png')
from IPython.display import Audio
Audio('test/400.mp3', autoplay=True)
From nowadays perspective mp3 could be considered as old and outdated. A current state of the art compression is called opus!