1# 2# @(#)Encode.opt 7.18 03/12/12 3# 4# xmcd - Motif(R) CD Audio Player/Ripper 5# 6# Copyright (C) 1993-2004 Ti Kan 7# E-mail: ti@amb.org 8# 9# This program is free software; you can redistribute it and/or modify 10# it under the terms of the GNU General Public License as published by 11# the Free Software Foundation; either version 2 of the License, or 12# (at your option) any later version. 13# 14# This program is distributed in the hope that it will be useful, 15# but WITHOUT ANY WARRANTY; without even the implied warranty of 16# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 17# GNU General Public License for more details. 18# 19# You should have received a copy of the GNU General Public License 20# along with this program; if not, write to the Free Software 21# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 22# 23# 24Encoding Method selector 25 26In "CDDA save to file" and "CDDA pipe to program" modes, 27if the output is set to a compressed format, then this 28menu allows you to set some related parameters. 29 30In lossy formats such as MP3, Ogg Vorbis, AAC and MP4, 31audio information is selectively dropped, based on 32psycho-acoustical models such that very high compression 33can be achieved while the perceived sound quality is 34minimally affected. 35 36In lossless formats such as FLAC, no audio information 37is dropped, so the result is not as highly compressed 38as the lossy formats, but sound quality is fully 39preserved. However, since the format is tailored for 40audio, it is more effective than generic data 41compression tools such as GNU zip. 42 43In either case, the process of compressing the CD audio 44is called "encoding". 45 46For lossy formats, you can specify the audio quality 47level desired. The higher the quality, the less 48information is dropped and the larger the output data 49(file size or streaming bandwidth) would be. The 50quality level is commonly expressed in terms of "bitrate" 51in kilobits per second (kb/s). 52 53The following describes the encoding concepts that the 54encoder operates in. 55 56CBR (constant bitrate) 57 58 In this mode, the encoding is done with a single, 59 unchanging bitrate. This is supported by the MP3 60 format. You can choose the bitrate using the "Bitrate" 61 menu. The higher you set the bitrate, the more you 62 trade increased file size in favor of quality. 63 Virtually all MP3 players support CBR encoded files. 64 65VBR (variable bitrate) 66 67 In this mode, the encoding is done with adaptive, 68 constantly changing bitrates. The encoder optimizes 69 the bitrate on-the-fly to maximize the quality of 70 the audio while keeping file size to a minimum. 71 Instead of specifying a bitrate to which the audio 72 data is to be encoded to, a "Quality factor" slider 73 is provided to alter the desired quality. The 74 Ogg Vorbis, AAC and MP4 formats are always VBR. 75 You may also encode to MP3 format in VBR mode, and 76 this is supported by many players. 77 78 For MP3 and Ogg Vorbis, you can optionally specify a 79 lower and upper bitrate boundary to be applied by the 80 encoder using the "Min" and "Max" bitrate menus. 81 82ABR (average bitrate) 83 84 In this method, varying bitrates are used similar 85 to the VBR methods. However, instead of specifying 86 a "Quality factor", you choose a bitrate to which 87 the encoder will use for an average value. 88 89 This is supported in MP3, Ogg Vorbis, AAC and MP4 90 formats. For MP3 and Ogg Vorbis, you may also 91 optionally choose lower and upper bitrate limits just 92 like in the VBR mode. 93 94You can choose the encoding method using this menu. The 95methods are format-specific, as described below: 96 97For MP3, the modes are as follows: 98 Mode 0 CBR 99 Mode 1 VBR, old algorithm 100 Mode 2 VBR, new algorithm (faster) 101 Mode 3 ABR 102 103For Ogg Vorbis and MP4, all modes are VBR, as follows: 104 Mode 0, 3 ABR 105 Mode 1, 2 Use a quality factor 106 107For FLAC, the modes are as follows: 108 Mode 0 None 109 Mode 1 Enable exhaustive LP quantization 110 coefficient search 111 Mode 2 Enable encoding verification 112 Mode 3 Enable both 1 and 2 113 114For AAC, all modes are VBR, as follows: 115 Mode 0 ABR, MPEG-2 116 Mode 1 Use a quality factor, MPEG-2 117 Mode 2 Use a quality factor, MPEG-4 118 Mode 3 ABR, MPEG-4 119 120 At the same bitrate or quality factor, there is no 121 sound quality difference between MPEG-2 and MPEG-4, 122 but some players support only one of these versions. 123 124For AAC and MP4, the bitrates selected in the bitrate 125menus are double the actual bitrate (e.g., if you 126select 128kbps, the actual bitrate used will be 64kbps). 127 128If you change the settings of these controls, they will 129take effect on the next "play" session. 130 131