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• How the ffmpeg astats crest factor is calculated

  30 août 2017, par FranGar

  I’m scripting a ffmpeg chain process for my work. The aim is normalizing/compressing lot of audio files (mp3’s).
  It’s done in Python and the critical part is the line :

  ffmpeg -y -i "Input.mp3" -codec:a libmp3lame -b:a 96k -af acompressor=threshold=-15dB:ratio=5:attack=0.01:release=1000:knee=2,dynaudnorm=g=3:m=2:p=0.95 "Output.mp3"

  The python script it’s complete and working BUT the nature of the audios (voice recordings) are very different so I can’t use the same params for all of them.

  I make some experimenting with the values of the ffmpeg filter astats and i discovered that the crest factor (Standard ratio of peak to RMS level ) gave a good reference to programatically get the better params.

  In fact I saw that a recording with a nice dynamic range sound and smooth in shape, get crest values around 9-15 (the compress/normlz params will be somehow conservative). But audios with crest around 22-30 need more aggressive processing.
  (All empirically)

  Somebody can clarify how the crest values are really calculated ? Which are the peaks taken to account ? (Why the flat factor is always 0 ?)
  Or if somebody knows how to get a value representing the sound ’smoothness’ will be nice also.

  Thanks for the ideas.

• ffmpeg to count words in audio text

  17 juillet 2020, par Joel Parker

  I am new to signal processing but wanted to take an audio file and determine how many words are spoken in one minute. I was thinking I could use the top of the loudness peaks to count the words but do not quite understand how to achieve this.

  


  First I used ffmpeg to remove the audio from the mp4 file I am using :

  


  ffmpeg -i courtcase.mp4 audiofile.mp4

  


  Then I tried to detect the loudness :

  


  ffmpeg -t 10 -i audiofile.mp4 -af "volumedetect" -f null /dev/null

  


  This produced some statistical information :

  


  video:157kB audio:1723kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[Parsed_volumedetect_0 @ 0x7fa6b26068c0] n_samples: 882000
[Parsed_volumedetect_0 @ 0x7fa6b26068c0] mean_volume: -20.6 dB
[Parsed_volumedetect_0 @ 0x7fa6b26068c0] max_volume: -4.0 dB
[Parsed_volumedetect_0 @ 0x7fa6b26068c0] histogram_4db: 64
[Parsed_volumedetect_0 @ 0x7fa6b26068c0] histogram_5db: 88
[Parsed_volumedetect_0 @ 0x7fa6b26068c0] histogram_6db: 220
[Parsed_volumedetect_0 @ 0x7fa6b26068c0] histogram_7db: 843



  


  I am not sure why it still shows 157kB of video, maybe my first command is wrong ?

  


  Anyway, assuming the file is just audio I found this command, which I believe shows dbm slices for 10 seconds :

  


  ffmpeg -i audiofile.mp4 -af astats=metadata=1:reset=1,ametadata=print:key=lavfi.astats.Overall.RMS_level:file=- -f null -


  


  and it produced a bunch of output :

  


  video:5782kB audio:63504kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[Parsed_astats_0 @ 0x7ff74c004bc0] Channel: 1
[Parsed_astats_0 @ 0x7ff74c004bc0] DC offset: 0.000240
[Parsed_astats_0 @ 0x7ff74c004bc0] Min level: -0.166239
[Parsed_astats_0 @ 0x7ff74c004bc0] Max level: 0.127112
[Parsed_astats_0 @ 0x7ff74c004bc0] Min difference: 0.000003
[Parsed_astats_0 @ 0x7ff74c004bc0] Max difference: 0.025335
[Parsed_astats_0 @ 0x7ff74c004bc0] Mean difference: 0.004455
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS difference: 0.006165
[Parsed_astats_0 @ 0x7ff74c004bc0] Peak level dB: -15.585332
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS level dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS peak dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS trough dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] Crest factor: 3.414311
[Parsed_astats_0 @ 0x7ff74c004bc0] Flat factor: 0.000000
[Parsed_astats_0 @ 0x7ff74c004bc0] Peak count: 2
[Parsed_astats_0 @ 0x7ff74c004bc0] Noise floor dB: nan
[Parsed_astats_0 @ 0x7ff74c004bc0] Noise floor count: 0
[Parsed_astats_0 @ 0x7ff74c004bc0] Bit depth: 32/32
[Parsed_astats_0 @ 0x7ff74c004bc0] Dynamic range: 72.297593
[Parsed_astats_0 @ 0x7ff74c004bc0] Zero crossings: 74
[Parsed_astats_0 @ 0x7ff74c004bc0] Zero crossings rate: 0.072266
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of NaNs: 0
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of Infs: 0
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of denormals: 0
[Parsed_astats_0 @ 0x7ff74c004bc0] Channel: 2
[Parsed_astats_0 @ 0x7ff74c004bc0] DC offset: 0.000240
[Parsed_astats_0 @ 0x7ff74c004bc0] Min level: -0.166239
[Parsed_astats_0 @ 0x7ff74c004bc0] Max level: 0.127112
[Parsed_astats_0 @ 0x7ff74c004bc0] Min difference: 0.000003
[Parsed_astats_0 @ 0x7ff74c004bc0] Max difference: 0.025335
[Parsed_astats_0 @ 0x7ff74c004bc0] Mean difference: 0.004455
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS difference: 0.006165
[Parsed_astats_0 @ 0x7ff74c004bc0] Peak level dB: -15.585332
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS level dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS peak dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS trough dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] Crest factor: 3.414311
[Parsed_astats_0 @ 0x7ff74c004bc0] Flat factor: 0.000000
[Parsed_astats_0 @ 0x7ff74c004bc0] Peak count: 2
[Parsed_astats_0 @ 0x7ff74c004bc0] Noise floor dB: nan
[Parsed_astats_0 @ 0x7ff74c004bc0] Noise floor count: 0
[Parsed_astats_0 @ 0x7ff74c004bc0] Bit depth: 32/32
[Parsed_astats_0 @ 0x7ff74c004bc0] Dynamic range: 72.297593
[Parsed_astats_0 @ 0x7ff74c004bc0] Zero crossings: 74
[Parsed_astats_0 @ 0x7ff74c004bc0] Zero crossings rate: 0.072266
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of NaNs: 0
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of Infs: 0
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of denormals: 0
[Parsed_astats_0 @ 0x7ff74c004bc0] Overall
[Parsed_astats_0 @ 0x7ff74c004bc0] DC offset: 0.000240
[Parsed_astats_0 @ 0x7ff74c004bc0] Min level: -0.166239
[Parsed_astats_0 @ 0x7ff74c004bc0] Max level: 0.127112
[Parsed_astats_0 @ 0x7ff74c004bc0] Min difference: 0.000003
[Parsed_astats_0 @ 0x7ff74c004bc0] Max difference: 0.025335
[Parsed_astats_0 @ 0x7ff74c004bc0] Mean difference: 0.004455
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS difference: 0.006165
[Parsed_astats_0 @ 0x7ff74c004bc0] Peak level dB: -15.585332
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS level dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS peak dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] RMS trough dB: -26.251394
[Parsed_astats_0 @ 0x7ff74c004bc0] Flat factor: 0.000000
[Parsed_astats_0 @ 0x7ff74c004bc0] Peak count: 2.000000
[Parsed_astats_0 @ 0x7ff74c004bc0] Noise floor dB: nan
[Parsed_astats_0 @ 0x7ff74c004bc0] Noise floor count: 0.000000
[Parsed_astats_0 @ 0x7ff74c004bc0] Bit depth: 32/32
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of samples: 1024
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of NaNs: 0.000000
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of Infs: 0.000000
[Parsed_astats_0 @ 0x7ff74c004bc0] Number of denormals: 0.000000
ts_time:368.268
lavfi.astats.Overall.RMS_level=-29.670653
frame:15861 pts:16241664 pts_time:368.292
lavfi.astats.Overall.RMS_level=-30.851195
frame:15862 pts:16242688 pts_time:368.315
lavfi.astats.Overall.RMS_level=-30.700943
frame:15863 pts:16243712 pts_time:368.338
lavfi.astats.Overall.RMS_level=-33.638604
frame:15864 pts:16244736 pts_time:368.361
lavfi.astats.Overall.RMS_level=-21.873170
frame:15865 pts:16245760 pts_time:368.385
lavfi.astats.Overall.RMS_level=-20.001936
frame:15866 pts:16246784 pts_time:368.408
lavfi.astats.Overall.RMS_level=-18.571318
frame:15867 pts:16247808 pts_time:368.431
lavfi.astats.Overall.RMS_level=-18.470749
frame:15868 pts:16248832 pts_time:368.454
lavfi.astats.Overall.RMS_level=-19.506688
frame:15869 pts:16249856 pts_time:368.477
lavfi.astats.Overall.RMS_level=-21.270579
frame:15870 pts:16250880 pts_time:368.501
lavfi.astats.Overall.RMS_level=-25.007862
frame:15871 pts:16251904 pts_time:368.524
lavfi.astats.Overall.RMS_level=-25.654372
frame:15872 pts:16252928 pts_time:368.547
lavfi.astats.Overall.RMS_level=-24.948357
frame:15873 pts:16253952 pts_time:368.57
lavfi.astats.Overall.RMS_level=-30.523540
frame:15874 pts:16254976 pts_time:368.594
....


  


  This is where I'm stuck. I think I have the information I need to determine the number of words spoken in a minute, except I don't know how to put all together. Also the last command just measures 10s slices, would I need to change that to 60s ? Does anyone know how to do this or if there is a better approach ?

  


• Interfacing to an Xbox Optical Drive

  1er octobre 2013, par Multimedia Mike — xbox

  The next generation Xbox is going to hit the streets soon. But for some reason, I’m still interested in the previous generation’s unit (i.e., the original Xbox). Specifically, I’ve always wondered if it’s possible to use the original Xbox’s optical drive in order to read Xbox discs from Linux. I was never curious enough to actually buy an Xbox just to find out but I eventually came across a cast-off console on a recycle pile.

  I have long known that the Xbox has what appears to be a more or less standard optical drive with a 40-pin IDE connector. The only difference is the power adapter which I surmise is probably the easiest way to turn a bit of standardized hardware into a bit of proprietary hardware. The IDE and power connectors look like this :

  
  
  

  Thus, I wanted to try opening an Xbox and plugging the optical drive into a regular PC, albeit one that supports IDE cables, and allow the Xbox to supply power to the drive. Do you still have hardware laying around that has 40-pin IDE connectors ? I guess my Mac Mini PPC fits the bill, but I’ll be darned if I’m going to pry that thing open again. I have another IDE-capable machine buried in my closet, last called into service when I needed a computer with a native RS-232 port 3 years ago. The ordeal surrounding making this old computer useful right now can be another post entirely.

  Here’s what the monstrosity looks like thanks to characteristically short IDE cable lengths :

  
  

  

  Click for larger image

  
  

  Process :

  1. Turn on Xbox first
  2. Turn on PC

  Doing these things in the opposite order won’t work since the kernel really wants to see the drive when booting up. Inspecting the 'dmesg' log afterward reveals interesting items :
  

  <br />
hdd: PHILIPS XBOX DVD DRIVE, ATAPI CD/DVD-ROM drive<br />
hdd: host max PIO5 wanted PIO255(auto-tune) selected PIO4<br />
hdd: UDMA/33 mode selected<br />
[...]<br />
hdd: ATAPI DVD-ROM drive, 128kB Cache<br />

  Why is that interesting ? When is the last time to saw disk devices prefixed by ‘hd’ rather than ‘sd’ ? Blast from the past. Oh, and the optical drive’s vendor string clearly indicates that this is an Xbox drive saying ‘hi !’.

  Time To Read
  When I first studied an Xbox disc in a normal optical drive, I noticed that I was able to read 6992 2048-byte sectors — about 14 MB of data — as reported by the disc table of contents (TOC). This is just enough data to play a standard DVD video animation that kindly instructs the viewer to please use a proper Xbox. At this point, I estimated that there must be something special about Xbox optical drive firmware that knows how to read alternate information on these discs and access further sectors.

  I ran my TOC query tool with an Xbox Magazine demo disc in the optical drive and it reported substantially more than 6992 sectors, enough to account for more than 2 GB of data. That’s promising. I then tried running 'dd' against the device and it was able to read… about 14 MB, an exact quantity of bytes that, when divided by 2048 bytes/sector, yields 6992 sectors.

  Future (Past ?) Work
  Assuming Google is your primary window into the broader internet, the world is beginning to lose its memory of things pertaining to the original Xbox (Microsoft’s naming scheme certainly doesn’t help searches). What I’m saying is that it can be difficult to find information about this stuff now. However, I was able to learn that a host needs to perform a sort of cryptographic handshake with the drive at the SCSI level before it is allowed to access the forbidden areas of the disc. I think. I’m still investigating this and will hopefully post more soon.