73 lines
1.9 KiB
Markdown
73 lines
1.9 KiB
Markdown
---
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title: Audio
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---
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# Bluetooth
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## Bluez
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- Using \`gdbus\` to introspect or retrieve properties
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``` bash
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gdbus introspect --system --dest org.bluez --object-path /org/bluez/hci0/dev_6C_C4_D5_6C_CF_19
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gdbus call --system --dest org.bluez --object-path /org/bluez/hci0/dev_6C_C4_D5_6C_CF_19 --method org.freedesktop.DBus.Properties.GetAll org.freedesktop.DBus.Properties
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```
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## Information on codecs
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- https://www.soundguys.com/understanding-bluetooth-codecs-15352/
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- https://habr.com/en/post/456182/
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- https://www.nytimes.com/wirecutter/blog/what-you-need-to-know-about-bluetooth-audio/
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- https://www.bluetooth.com/learn-about-bluetooth/recent-enhancements/le-audio/le-audio-specifications/
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- https://www.bluetooth.com/blog/best-recorded-bluetooth-presentations-from-2020/
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## Transport payload sizes observed for SBC
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- SBC-XQ @ 552 Kbps: 622 bytes
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- SBC-XQ @ 512 Kbps: 574 bytes
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- SBC-XQ @ 453 Kbps: 678 bytes
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# Random
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## Clean up audio with Audacity
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Consider an mkv file recorded with OBS, do the following
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- Extract the audio from video file
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``` bash
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ffmpeg -i infile.mp4 -acodec copy outfile.aac
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```
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The option -acodec copy implies to not re-sample the audio.
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- Use Audacity's noise reduction filters. Export as m4a.
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- Merge audio and video again
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``` bash
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ffmpeg -i infile.mp4 -i denoised-audio.m4a -vcodec copy -acodec copy -map 0:0 -map 1:0 denoised-video.mp4
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```
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- Increase the volume using ffmpeg
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``` bash
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ffmpeg -i infile.mkv -vcodec copy -filter:a "volume=5.000000" infile-outputlouder.mkv
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```
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Note that this command seems to change the format in mkv file from aac to ogg.
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To keep the codec same namely AAC, use the following
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``` bash
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ffmpeg -i infile.mp4 -vcodec copy -filter:a "volume=3.000000" -c:a aac -b:a 320k infile-outputlouder.mkv
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```
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See the link <https://trac.ffmpeg.org/wiki/Encode/AAC>
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