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QTSource & 24-bit audio 
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Joined: Thu, 2012/03/08 2:37 pm
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Unread post QTSource & 24-bit audio
Hey tateu - First off, great plugin! Today I have a need that QTSource doesn't seem to meet. I have a ProRes with 8 channels of 24-bit audio, which I need to keep 24-bit. I have the latest build of QTSource, and with audio=2 it seems to be converting the audio to 16-bit. Is there a switch I'm not aware of, or any other solution to keep 24-bit faithful in the script? Thanks!


Thu, 2012/03/08 4:16 pm
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Joined: Sun, 2005/04/03 7:02 pm
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Location: Los Angeles, CA USA
Unread post Re: QTSource & 24-bit audio
Hmm...No there is not. Let me spend a few minutes looking into it tonight, maybe it's something I can quickly add in. I'll try to post back around 10 or 11pm Pacific time tonight.

In the mean time...ffmpeg has had a prores decoder for several months. You might want to give FFMpegSource a try. It didn't quite work for me, though. My 24 bit audio was converted to 32 bit by FFMpegSource. Also, ffmpeg has two different prores decoders, one by the ffmpeg development team and one by the LibAV development team. I believe that FFMpegSource uses the one by the LibAV team and that one has always been a bit buggy. It creates lots of wrongly decoded blocks on my video. You can see the examples below. The first one decodes a Prores file using the publicly available FFmpegSource and the 2nd uses a custom FFmpegSource that I compiled.


Attachments:
File comment: FFMpegSource v2.17 & r644 using Prores_lgpl codec by LibAV Team
FFmpegSource2_v2.17_Prores_lgpl_by_LibAV.png
FFmpegSource2_v2.17_Prores_lgpl_by_LibAV.png [ 4.25 KiB | Viewed 8076 times ]
File comment: Custom FFMpegSource using Prores codec by FFMpeg Team
FFmpegSource2_Custom_Prores_by_FFMpeg.png
FFmpegSource2_Custom_Prores_by_FFMpeg.png [ 4.28 KiB | Viewed 8076 times ]
Thu, 2012/03/08 4:56 pm
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Joined: Thu, 2012/03/08 2:37 pm
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Unread post Re: QTSource & 24-bit audio
Wow, fast reply! Thanks for looking into this - really appreciated. I'll play with FFMpegSource - the video would be a problem, but the audio may not be. SSRC also converts to 32-bit, however when converting back to 24-bit with ConvertAudioTo24bit(), the extra 8 bits that were padded, get removed cleanly as well. I can prove that by feeding it a 24-bit DolbyE WAV, which would not decode if anything but padding/truncation was taking place. The same may be true for FFMpegSource, and possibly QTSource if it also returns 32-bit (which I'd also be interested in playing with). Thanks again, and I'll keep my fingers crossed!


Thu, 2012/03/08 5:10 pm
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Unread post Re: QTSource & 24-bit audio
My first test looks promising...A new build of QTSource with a few changes is reporting 24 bit audio output. I don't have the latest source code here at work, so like I said above, expect to see a another post around 10 or 11pm Pacific time tonight. I will hopefully have a new build for you to test.


Thu, 2012/03/08 5:46 pm
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Unread post Re: QTSource & 24-bit audio
Ok, give the attached version a try. For some reason, I was explicitly setting all audio to 16bit. I had two functions that tried to read the source bits per channel. For 24 bit audio, one of my functions was returning 16 bit and the other one was returning 32 bit. Maybe that's why I decided to just set all audio to 16 bit...because I couldn't be sure if either of those were correct. Today, I found a 3rd way to check the source format and this one returned the correct value of 24 bit for the test files I tried it on.

Hopefully this change doesn't break something else. I first started working on QTSource back in 2005. Who can remember everything from that far back?


Attachments:
File comment: Correctly interpret 24bit and 32bit audio formats with QTInput
QTSource_20120308.zip [72.44 KiB]
Downloaded 472 times
Thu, 2012/03/08 11:13 pm
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Joined: Thu, 2012/03/08 2:37 pm
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Unread post Re: QTSource & 24-bit audio
You seem to have nailed it tateu! I used a QT source with a 24-bit track containing DolbyE, exported a WAV, and decoded the DolbyE just fine, proving it's bit perfect. I'll be sure to let you know if I find any weirdness with this build. Thanks!


Fri, 2012/03/09 6:09 pm
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Unread post Re: QTSource & 24-bit audio
Your welcome. Glad it worked for you.


Fri, 2012/03/09 6:20 pm
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