acm_open_decoder(): Support force_chans = -1 for "always trust header" #3
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In hindsight I think having such override in decode.c is simply wrong. Forcing channels should be purely decision of caller, like acmtool does with command line flags. There should be no extra flag needed to accept channel info from file. Please just remove the condition to override file channels. |
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If what the comment in the code says is true, and it's only plain ACM files that get this wrong (but not always), while WAVC files always get it right, then the decision is harder to make for the caller, as they don't have the information about what kind of ACM file it is, at least not without parsing the header themselves or opening once to figure out the type and then (possibly) again with |
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Well, there are no new ACM files created and for specific game the user/emulator will know what files are correct or not - or whether all of them are OK. I remember that it was systematic problem with specific games like iwd/planescape, but there is no way to encode such knowledge to decode.c, thus it is much better if such override happens somewhere such context is known. |
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Assuming that there are games that use both plain ACMs and WAVC ACMs, deciding this on the client-side seems like a PITA. Maybe it should be switched and |
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Digged through some archives - iwd has both wavc and bad-1-chan acm, so yeah such mode could be useful. So activating the workaround via |
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Ok, I'll change the code (and docs) accordingly tomorrow :) |
force_chans = 0 used to assume that plain ACM files are stereo (even if their header says mono), as apparently that's the case for the files from some games - but not all, Descent3 has both mono and stereo ACM files, and their headers specify the correct number of channels, so this quirk turns out to be a bad default, especially when there is no way to tell libacm to trust the header. Now force_chans = 0 assumes that the header is always correct, and the old quirk mode (that assumes that plain ACM files are always stereo, but the headers of "WAVC" ACM files are always correct) can be enabled with force_chans = -1.
mostly the parts that weren't obvious to me from the function/argument names including the new behavior for force_chans
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Ok, I made these changes - now force_chans = 0 always trusts the header and force_chans = -1 enables the old workaround. Additional benefit: If other quirk modes come up in the future (who knows in what ways ACM files of other games are buggy..), they could be added with force_chans = -2, force_chans = -3 etc |
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Merged, thanks! |
Descent3 has both mono and stereo ACM files, and their headers appear to specify to correct number of channels.
Support that with
force_chans = -1.While at it, I added some documentation.