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128 lines
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5.1 KiB
Text
128 lines
No EOL
5.1 KiB
Text
Windows ACM (Audio Compression Manager) DLL library
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PURPOSE
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This directory contains support for loading and using Windows ACM
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(Audio Compression Manager) codecs from the native Windows DLL files.
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Its purpose is to allow Linux programs running on the x86 architecture
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to use proprietary Windows audio codecs. This enables Linux
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users to interoperate with Windows users without
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reverse engineering the codec completely from scratch.
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For example, it should be straightforward to write a Linux
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program based on this library to allow TrueSpeech encoded
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.wav files to be exchanged with Windows users. Indeed, the provided
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test program comes close to doing that, but for coding simplicity
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it does not use .wav headers.
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ACKNOWLEDGMENTS
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This code was extracted from the mplayer project (http://mplayerhq.hu),
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which apparently extracted it from the Wine project (http://winehq.org).
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It was slimmed down to support only the ACM audio codecs and not
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video codecs. See the CREDITS file for details.
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REQUIREMENTS
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To use the included TrueSpeech test program, the following Windows
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DLLs are required:
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tsd32.dll
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tssoft32.acm
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Other codecs may require other DLL files. A good source of
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DLL files is the w32codecs archive, available at
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http://mplayerhq.hu/MPlayer/releases/codecs/win32codecs.tar.bz2
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Debian users can install it using "apt-get install w32codecs".
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Unfortunately, version 0.9 of w32codecs does not contain tsd32.dll.
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You may need to obtain it via other means, such as copying it from
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your Windows installation.
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INSTALLATION
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The code is a library to be used in a larger program. To compile
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it separately:
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vi config.h # edit as needed
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vi Makefile # edit as needed
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make
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This will build the output files libwin32acm.a and test_truespeech.
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USAGE
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test_truespeech.c contains an example program to demonstrate use of
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the ACM under Windows and to test the library with the TrueSpeech
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codec. More documentation about using the ACM library functions
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under Windows can be found at http://microsoft.com, specifically
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http://msdn.microsoft.com/library/default.asp?url=/library/en-us/multimed/audcomp_3kc2.asp
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Or search for ACM on Microsoft's site.
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test_truespeech exercises the TrueSpeech
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codec. It will read the file pcmin.raw in the current directory
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and encode it via the TrueSpeech codec and write the result
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to truespeechout.raw. It will then decode truespeechout.raw and
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and produce the file pcmout.raw. Because TrueSpeech is a lossy
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codec, the file pcmin.raw is not byte-for-byte identical to pcmout.raw,
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however they should sound very similar.
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The files pcmin.raw and pcmout.raw can be played with the sox
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utility "play" under Linux as follows. The options are
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required because there is no header information in the file to inform
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the player what format the file is in:
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play -f s -r 8000 -c 1 -s w pcmout.raw
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An example pcmin.raw file is included.
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The format of the pcmin.raw file is PCM (pulse code modulation)
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with 16-bit signed linear samples, mono (1 channel), at 8 KHz sampling rate.
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It is basically a .wav file with the WAV headers removed, and can
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be generated via the sox utility under Linux using options similar
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to the "play" line above (specify a conversion
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to .raw format). truespeechout.raw is a raw TrueSpeech file and
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is approximately 1/15 the size of the input file. It is normally
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not playable directly under Linux, although mplayer and some other
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players which load the TrueSpeech DLL like this library does can
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convert it to PCM on the fly for playing.
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If you would like to use the library with other ACM codecs besides
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TrueSpeech, read the file CODECS for more information.
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win32codec.h and win32codec.c contain a simple wrapper around the
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ACM codec functions to aid their use in Linphone. They can be
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considered as another example.
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TIPS FOR DEVELOPERS
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As shown in test_truespeech.c, the same input and output buffers
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can be used for each block of data to convert without calling
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acmStreamPrepareHeader() and acmStreamUnprepareHeader() over and
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over. But if your application is using a different buffer for
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each block of data, it is quite allowable to prepare and unprepare
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the buffers each time a new block of data is converted. This is
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what mplayer does, and it is also done in win32codec.c. Microsoft's
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documentation about the ACM API is good, but the test_truespeech.c
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example should be quite helpful.
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Microsoft's documentation does not clearly mention
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that often a codec used in encoding mode requires
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ACM_STREAMOPENF_NONREALTIME to be passed to
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acmStreamOpen() or it will fail to open. This
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parameter indicates that realtime operation is not required.
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In the case of TrueSpeech, although the codec can operate perfectly
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well in realtime on a modern PC, it appears the designers were conservative
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and acmStreamOpen() will fail if realtime operation is requested.
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When converting from one proprietary codec format to another,
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often 16-bit signed linear PCM must be used as an intermediate codec
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step. Most codecs will support 16-bit signed linear PCM at a minimum
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in addition to their own format. See CODECS for details on
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using the library with ACM codecs besides TrueSpeech.
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Robert W. Brewer <rbrewer at op.net>
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2003-05-31 |