A few more
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Atlantis -The Lost Tales - Tracks 2 (Awakening) & 3 (Rhêa) of the OST on The Internet Archive
and [url=https://archive.org/details/Rhea-AtlantisTheLostTales]here in MP3 and OGG format.
Plus some low quality track-samples on
RPGFan.
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Atlantis 2: Beyond Atlantis - So far, only some low quality track-samples on
RPGFan.
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Avadon: The Black Fortress - According to this
RPGFan review, the game has no in-game music (also mentioned in the cons of the game):
With the exception of a single opening theme track (which ain't half bad), there is no music whatsoever.
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Avadon 2: The Corruption - According to this
RPGWatch review, this one also comes with no in-game music:
Sound is another area where some might be divided, as the only music you will hear in the game happens on the starting menu and nowhere else.
Maybe you should consider moving these two games to the "Games Without Music" list? The only place I found the mentioned themes is on YouTube.
I also think that
Geneforge 1-5 and
Avernum: The Complete Saga probably fall into this category as well - Bjørn A. Lynne and Adam Skorupa are listed in the credits of a few of these games on Mobygames (Intro Music), but I couldn't find anything on their sites (or anywhere else besides YouTube).
Plus, I got the Humble Weekly Sale: Spiderweb RPGs and no soundtracks were included.
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Back to the Future: The Game - One that my friend checked with Telltale Music Extractor. Open the Packs folder, set an output folder and after clicking on the "Go" button, all music files are extracted in OGG format.
-- Wallace & Gromit's Grand Adventures - I noticed that you didn't include this game - did it come with a soundtrack on GOG?
Another one that my friend checked with Telltale Music Extractor. Open the Packs folder, set an output folder and after clicking on the "Go" button, all music files are extracted in OGG format. What's interesting about this game is that Telltale Music Extractor dumps the files as a soundtrack which means it creates numbered tracks and a CD cover.
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Costume Quest - Again had a friend test DoubleFine Explorer. The music is in the files within the subfolders of the Audio folder (Costume Quest\Win\Audio\Music and Costume Quest\Win\Audio\Music_DLC). One needs to select each of the .fsb files and DoubleFine Explorer finds all music files and lets you save them to a folder of your choice in MP3 format.
I know we have a commercial OST for this one, but maybe you can add this as an alternative.
I assume it works the same way on
Psychonauts (.fsb files in an "Audio" folder), but none of my friends or me have it on GOG.
I've got another friend that has Brütal Legend, but he can't install and test it before the weekend, so we'll have to wait for the details on this one.
And I think that with Brütal Legend we will have covered all Telltale and Double Fine games, right?
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Empire Earth: Gold Edition - the music files are in .dls format and the only tool I found so far to extract and convert them to MP3 format is a commercial application (FMJ Awave Studio which costs $99, so not a viable solution).
I assume the same goes for Empire Earth 2 Gold Edition and Empire Earth 3, but I don't have them so can't check them.
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Real Myst - Real Myst 3D is listed as supported by Dragon UnPACKer, so I thought maybe it'll work on GOG's version too. I don't have the game, so I (again) had a friend check it with Dragon UnPACKer and he (again) had success. One needs to open the mara.dni and pera.dni files, within them is a folder named "wav" with a number of subfolders which contain various music (possibly also sound) files in WAV format.
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SiN Gold - Another one I don't have, but luckily a friend does and one that Dragon UnPACKer works on too. One needs to open the pak0.sin file (Sin Gold\2015), within it is a folder labelled "music" with a number of subfolders which contain various music files in WAV format.
I've also contacted the developer of Telltale Music Extractor and asked him if he's still considering to add support for MP3 and WAV.
P.S. I saw that Eniena edited his post to mention the Telltale games, but I included them anyway to provide details.