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general: linux audio extract now considers actual header len #57

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18 changes: 15 additions & 3 deletions content/docs/wiki/general/audio-file-format.md
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Expand Up @@ -76,9 +76,21 @@ But the in experiments used encoder did not have an obvious feature to do this.

**We have developed a tool called [teddy](https://github.com/toniebox-reverse-engineering/teddy) to encode and decode these files.**

# Audio file extraction with Linux OS
- Remove Header of the file with ´dd bs=4096 skip=1 if=500304E0 of=trim.ogg´
- then just use ffmpeg to convert it into mp3 ´ffmpeg -i trim.ogg done.mp3´
# Audio file extraction with Linux OS and bash shell

1. read the *header_len* (in hex): `dd status=none if=50012345 bs=1 count=4 | xxd -plain`
2. convert to decimal and add 4 in order to get the length (in decimal) of the whole header
3. read the audio_data into file: `dd if=50012345 bs=1 skip="${header_len}" of=50012345.audio_data.ogg`
4. (optional) convert audio_data from ogg to mp3: `ffmpeg -i 50012345.audio_data.ogg 50012345.audio_data.mp3`

The same procedure as one block of spagetthi code for easier copy&paste:

```bash
inputfile=50012345
header_len="$((4+0x"$(dd status=none if="${inputfile}" bs=1 count=4 | xxd -plain)"))"
dd if="${inputfile}" bs=1 skip="${header_len}" of=${inputfile}.audio_data.ogg
ffmpeg -i "${inputfile}.audio_data.ogg" "${inputfile}.audio_data.mp3"
```

# Audio file extraction with Windows
- Remove Header of the file with: powershell -Command "$in = [System.IO.File]::OpenRead('00000000'); $out = [System.IO.File]::Create('trim.ogg'); $in.Seek(4096, 'Begin') | Out-Null; $in.CopyTo($out); $in.Close(); $out.Close()"
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