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187 lines
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187 lines
9.0 KiB
Plaintext
/*
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* @(#) MPEG Audio Player maplay 1.2, last edit of this file: 6/23/94 13:02:49
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* @(#) Copyright (C) 1993, 1994 Tobias Bading (bading@cs.tu-berlin.de)
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* @(#) Berlin University of Technology
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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This is the README file of the MPEG Audio Player maplay, Version 1.2.
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Besides this file, you should now own a copy of the following files:
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ANNOUNCEMENT the announcement for this release
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INSTALL infos about compiling and installing the program
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COPYING the GNU General Public License
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Makefile a makefile
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configuration.sh a shell script used by the makefile
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and the source files
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all.h maplay.cc subband_layer_1.h
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crc.cc obuffer.cc subband_layer_2.cc
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crc.h obuffer.h subband_layer_2.h
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header.cc scalefactors.cc synthesis_filter.cc
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header.h scalefactors.h synthesis_filter.h
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ibitstream.cc subband.h ulaw.cc
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ibitstream.h subband_layer_1.cc ulaw.h
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-------------------------------------------------------------------------------
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0) Introduction
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MPEG is a standard created by the ISO (International Organization for
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Standardization) and the IEC (International Electrotechnical Commission).
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The full name of this standard is "ISO/IEC DIS 11172: Information
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Technology - Coding of moving pictures and associated audio for digital
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storage media ut to about 1.5 Mbit/s". As the name already states,
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it deals with digital video and audio. The video part of this standard has
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inspired many people to write decoders and a few encoders for it.
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Best known should be the Berkeley player. Players for the audio part on
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the other hand are very rare. The ones I know are the XING player for Windoze
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and a sample implementation of the ISO, which also includes an encoder.
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The audio part of the MPEG standard specifies three layers, whereat each
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layer specifies its own file format. All three layers are using similar
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audio coding techniques, but they vary in efficiency and complexity.
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Layer I needs the fewest calculation time for en-/decoding a stream, layer III
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the most. But a layer I MPEG audio stream is bigger than a layer III stream
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at the same quality. This program is able to decode and play only layer I
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and II streams, layer III is not supported (yet?!?).
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Like the MPEG video standard, the audio part also uses a lossy compression
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algorithm, which means that you can't get back 100% the original from a
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MPEG audio stream. Layer II MPEG audio streams are compressed by ratios
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from 1:3 up to 1:24 compared to raw PCM data, like on an audio CD.
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But the quality is still very (very) near to the original at ratios between
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1:5 and 1:12. You'll love it... :-)
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-------------------------------------------------------------------------------
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1) What does maplay?
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maplay version 1.2 is the second release of my MPEG audio player/decoder.
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It decodes layer I and layer II MPEG audio streams and plays them
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using a CD-quality audio device. Currently supported devices are the
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dbri device of SPARC 10 computers and the audio ports of Silicon
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Graphics Indigo machines. Thanks to Louis P. Kruger (lpkruger@phoenix.
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Princeton.EDU), maplay 1.2 can also use the /dev/dsp device under Linux.
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Louis has tested it with the Pro Audio Spectrum 16 soundcard. Sound Blaster 16
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and Gravis Ultrasound cards should also work, but a bug in the dsp driver
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prevents stereo playback on Gravis Ultrasound cards. An amd device of a
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SPARC 2/IPX/... machine can be used, too, but this device is only capable of
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producing audio output at 8 kHz in u-law format, which sounds like transmitted
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through a telephone. Other audio device are not supported directly, but can be
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used with the "decode to stdout" option and an audio format converter.
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Besides it shouldn't be a problem to adapt the program to other audio devices.
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The player supports all modes, which are single channel, stereo,
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joint stereo and dual channel, and all bitrates except free mode.
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The missing free mode support should not be a problem for now,
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because I haven't seen such a stream yet.
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maplay needs approximately 46% CPU time on SPARC 10/40 machines and 50%
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on Indigos for realtime stereo playback of a 44.1 kHz 128 kbit/s stream.
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Single channel playback needs about the half CPU time. On a SPARCstation IPX,
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maplay needs about 43% CPU time for realtime mono playback. Stereo playback
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is not possible via an amd device.
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Besides realtime playing of audio streams, maplay can decode streams to
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stdout for further conversions. The output consists of 16 bit signed PCM
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values. For stereo streams, the values are interleaved, which means that
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a value for the left channel is followed by a value for the right channel
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and so on. If maplay has been compiled for u-law output, the output consists
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of 8 bit u-law samples at a rate of 8 kHz, no matter what frequency the stream
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uses.
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-------------------------------------------------------------------------------
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2) How to create a maplay binary?
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Please read the install file for this topic.
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-------------------------------------------------------------------------------
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3) How to start the program?
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For a quick mono test enter "./maplay -v -l filename", where filename is the
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name of an audio stream, like "things.mp2". This stream has been posted along
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with the sources and is the beginning of Roxette's song "Things Will Never Be
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The Same". It is coded in joint stereo mode with 128 kbit/s, which is a
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compression ratio of 1:11. If the output is ok, you can test stereo playback
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by leaving out the -l option. If the stereo output stutters, the problem is
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not enough free CPU time in most cases. Stereo output is not possible when
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using an amd u-law device. If maplay shows error messages like
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"ioctl AUDIO_GETDEV on /dev/audio: ..."
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and maplay was compiled for u-law output, please try out the -amd option.
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This option forces maplay to treat /dev/audio as an amd device and may be
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required on SPARC clones.
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To convert a MPEG audio stream into other audio formats, you can use
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"maplay -v -s filename | your_converter". Unfortunately, I can't be of much
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help for you to find such a converter. The only good converter I know is the
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"soundfiler" on Indigos. But if you would have an Indigo, you wouldn't need a
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converter...
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-------------------------------------------------------------------------------
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4) Command line options
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maplay [-v] [-s] [-l] [-r] [-us] [-uh] [-ul] [-amd] [-c] [-f ushort] filename
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with these options:
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filename filename of a MPEG audio stream or - for stdin
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-h short help
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-v verbose mode
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You will get information about the stream, like mode, bitrate,
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copyright etc., if you use this option.
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-s stdout mode
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This option tells the program to decode the stream to stdout.
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The created output contains 16 bit signed PCM samples. If the
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binary has been compiled for 8 kHz u-law format usage, the
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output consists of 8 bit u-law samples at a 8 kHz rate. If the
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stream is in stereo mode, the samples of both channels are
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interleaved, the sample for the left channel first.
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-l maplay decodes (and plays) the left channel of stereo streams
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only. This option halves the required CPU time.
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-r Same as above, but decodes the right channel only
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-us, -uh These options are available on SPARCstations only.
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They specify where the audio signal should be send to:
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"-us" means speaker and "-uh" headphone jack.
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-ul This option is available on machines with the dbri device
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and sends the audio output to the line out jack.
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-amd This option forces maplay to treat /dev/audio as an amd
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device. Use it if your SPARC clone has an amd device, but
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maplay doesn't recognize it. You may also use this option on a
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machine with a dbri device, because the dbri device can also
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produce u-law output. But I suggest to recompile the program
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without the ULAW define in this case to get the CD-quality
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output.
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-c This option instructs the program to report filter range
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violations to stderr. Sometimes PCM values calculated by
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the synthesis filter exceede the 16 bit boundary and must
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be mapped to these boundaries. If you can hear this, you
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may use the next option.
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-f ushort maplay uses this scalefactor instead of the default value 32768
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for the synthesis filter. You can reduce or eliminate range
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violations with this option, but lower scalefactor values
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reduce the signal-to-noise ratio, too. I can't remember when
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I used this option the last time myself.
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Ok, that's all for now and this release,
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I hope you like it,
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Tobias Bading (bading@cs.tu-berlin.de)
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