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I have an old .avi file where the sound is just scratchy, no mystery there but I have a wmv file presumably derived from the .avi file but the wmv HAS the sound. Has anyone any ideas what may have happened and how to fix it?

Quick background:

In 2006 we recorded a birthday party with my girlfriends computer, it was running XP and recording was done with a Logitech Quickcam for notebooks probably using quickcapture (quickcam 8.4.8). My girlfriend then edited parts of the clips in Windows Movie Maker, converting it to a .wmv and sent it to our friends. However, in the original clips a friend of mine held a hilarious monolog and subsequently fell off the chair. I really want this clip for a thing we are doing for his stag-party.

NOW, The how can the original avi clip have weird scratchy sound, just static really, and the edited version, a wmv clip, have perfect sound? I ran them through mediainfo and got the data attached below.

I have tried the following without success:

  • Recoding the avi to different format.
  • Using audacity to check the sound profile, and the avi has a sound profile that looks like solid band of static with a few spikes. I have tried every filter on audacity with out result
  • Firing up the old computer and checking if the sound is there – it is not but the original has been copied to different folders since it’s creation. I tried to replicate the situation with the cam, first recording then running through moviemaker but those clips retain the sound.

If the file is simply corrupt it must have happened when my girlfriend moved it to another folder in the same computer and it must have happened with all the avi files from the Logitech cam (they all have the same problem). Is this likely?

Could the Logitech software have used some weird codec or mux that subsequently disappeared in later updates so that the current software uses the wrong demux or codec to open the avi?

Could the program have written the wrong demux /codec info into avi? Is there a player where I can force the use of a specific codec to test this. Could it be some sort of little-endian – Big-endian issue?

Please someone help me with this!

Complete name                           Video 3.avi  (without sound) last change:   2006-08-20 16:46

Format                                   : AVI 
Format/Info                              : Audio Video Interleave 
File size                                : 145 MiB 
Duration                                 : 7 min 55 s 
Overall bit rate                         : 2 556 kb/s 
IsTruncated                              : Yes 

Video
ID                                       : 0 
Format                                   : Indeo 4 
Codec ID                                 : IV50 
Codec ID/Info                            : Intel Indeo Video 5.0 Wavelet 
Duration                                 : 7 min 55 s 
Bit rate                                 : 2 378 kb/s 
Width                                    : 640 pixels 
Height                                   : 480 pixels 
Display aspect ratio                     : 4:3 
Frame rate                               : 15.000 FPS 
Bits/(Pixel*Frame)                       : 0.516 
Stream size                              : 135 MiB (93%) 
Title                                    : qc2.avi Video #1 

Audio
ID                                       : 1 
Format                                   : PCM 
Format settings, Endianness              : Little 
Format settings, Sign                    : Unsigned 
Codec ID                                 : 1 
Duration                                 : 7 min 55 s 
Bit rate mode                            : Constant 
Bit rate                                 : 176.4 kb/s 
Channel(s)                               : 1 channel 
Sampling rate                            : 22.05 kHz 
Bit depth                                : 8 bits 
Stream size                              : 10.0 MiB (7%) 
Alignment                                : Aligned on interleaves 
Interleave, duration                     : 2954  ms (44.32 video frames) 
Title                                    : qc2.avi Audio #1 

 
Complete name                         Party 2006.wmv  (With sound) last change:2006-08-20 17:43
Format                                   : Windows Media
File size                                : 26.4 MiB
Duration                                 : 4 min 13 s
Overall bit rate mode                    : Constant
Overall bit rate                         : 873 kb/s
Maximum Overall bit rate                 : 874 kb/s
Encoded date                             : UTC 2006-08-20 16:40:48.328
Application                              : Windows Movie Maker 2.1.4026.0

Video
ID                                       : 2 
Format                                   : VC-1 
Format profile                           : MP@ML 
Codec ID                                 : WMV3 
Codec ID/Info                            : Windows Media Video 9 
Codec ID/Hint                            : WMV3 
Description of the codec                 : Windows Media Video 9 
Duration                                 : 4 min 13 s  
Bit rate mode                            : Constant 
Bit rate                                 : 768 kb/s 
Width                                    : 640 pixels 
Height                                   : 480 pixels 
Display aspect ratio                     : 4:3 
Frame rate                               : 25.000 FPS 
Color space                              : YUV 
Chroma subsampling                       : 4:2:0 
Bit depth                                : 8 bits 
Scan type                                : Progressive 
Compression mode                         : Lossy 
Bits/(Pixel*Frame)                       : 0.100
Stream size                              : 23.2 MiB (88%) 
Language                                 : Swedish 

Audio
ID                                       : 1 
Format                                   : WMA 
Format version                           : Version 2 
Codec ID                                 : 161 
Codec ID/Info                            : Windows Media Audio 
Description of the codec                 : Windows Media Audio 9.1 -  96 kbps, 44 kHz, stereo (A/V) 1-pass  CBR
Duration                                 : 4 min 13 s 
Bit rate mode                            : Constant 
Bit rate                                 : 96.0 kb/s 
Channel(s)                               : 2 channels 
Sampling rate                          : 44.1 kHz 

I have extracted the audio from the original avi file using ffmpeg to a wav file with the same bit and samplingrate. The result from audacity is below. However Audacity does not seem to want to open the file in 8 bit. I tried wavosaur with the same result. Picture of waveform in audacity - the grey box is a section that I tried declipping with audacity. To the very left is a close zoom of the curve

Attached clip of audio with unchanged format is found here Download clip

enter image description here

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Unfortunately I believe Dirkt is right. There simply is no sound on the avi. I took help from a friend to check that I extracted the audio correctly using ffmpeg, option -acodec copy. Looking at the hex dump for the entire sound clip I get pretty much what is seen in Dirkt's Answer. Looking at a hex dump for the whole avi I get the same result (at least if I have correctly guessed what parts are the sound). Basically silence but with a lot of static.

Having ruled out codec issues using ffplay -i c:\ffmpeg\video3.avi -acodec [xxxx] to force the player to use a specific codec I can only draw the conclusion that the avi I have is not the original and for some reason the sound is simply not there. Some sort of conversion issue perhaps.

Thanks for taking your time to help me with this and for bearing with a beginner. At least I learned a lot about AV files and decoding.

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Partial answer: The "scratchy" sound has a sample rate of 22.05 kHz, which is half of the usual 44.1 kHz. This means if anything in the playing chain tries to upsample it, there's a danger of aliasing. Other possible sources of "scratchy" sound are clipping or unusual muxing.

So the first step is to extract the sound and convert it e.g. to a WAV file, keeping the format. You can do that for example with ffmpeg, option -acodec copy. That should get rid of any odd muxing, so if it plays after that, this was the problem.

Next step is to have a look at the waveform in an audio editor like audacity, and find out the exact problem. Which means you need to give us some data, or include a picture of a relevant part with the waveform stretched enough to be visible, unless you can spot the problem yourself. The final step is to correct whatever is wrong, e.g. try some upsamplers to get it to 44.1 kHz, or find a declipper that works on it, or whatever is necessary.

Edit

The clip with unchanged format just contains silence. Part of a hexdump, the rest looks similar:

00000060  80 80 80 80 80 80 80 80  80 80 7f 80 7f 80 7f 80   
00000070  80 80 80 7f 80 7f 80 7f  80 7f 80 80 80 80 80 80

80 and 7f are "middle" values very close to what would be zero in signed format.

So if you can actually here something on the original AVI, that is someone speaking, just distorted and "scratchy", then whatever you did to arrive at this clip erased that information. Or you picked a part that was silence.

  • Thanks! I'll try that with the ffmpeg. I am already working on trying the player do a selected decoder. – Carl-Fredrik von Essen Jun 28 '17 at 11:38
  • I have added a picture of the waveform. – Carl-Fredrik von Essen Jun 28 '17 at 22:07
  • I said "stretched enough to be visible". Try zooming in horizontally (on the time axis). Also, the format conversion seems to have gone wrong - the original format was unsigned PCM, the Audacity image is signed, but only negative. – dirkt Jun 28 '17 at 22:13
  • Sorry that was the wrong file. – Carl-Fredrik von Essen Jun 29 '17 at 10:14
  • See edited question. However, no matter what I do the waveform looks like a solid static. It is the same in other audioprograms such as wavosaur. In the new picture I have tried some declipping but with no result. – Carl-Fredrik von Essen Jun 29 '17 at 10:15

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