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comparison decoders/mp3.c @ 96:25e515dfa18d

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Fix for MP3 detection.
author Ryan C. Gordon <icculus@icculus.org>
date Tue, 02 Oct 2001 17:46:12 +0000
parents 40006625142a
children 6d9fdec2f708
comparison
equal deleted inserted replaced
95:4436f4587c9a 96:25e515dfa18d
99 SMPEG *smpeg; 99 SMPEG *smpeg;
100 SMPEG_Info smpeg_info; 100 SMPEG_Info smpeg_info;
101 SDL_AudioSpec spec; 101 SDL_AudioSpec spec;
102 Sound_SampleInternal *internal = (Sound_SampleInternal *) sample->opaque; 102 Sound_SampleInternal *internal = (Sound_SampleInternal *) sample->opaque;
103 SDL_RWops *refCounter; 103 SDL_RWops *refCounter;
104 Uint8 mp3_magic[2];
105 104
106 output_version(); 105 output_version();
107 106
108 /* 107 /*
109 * SMPEG appears to be far too greedy about what it accepts as input. 108 * If I understand things correctly, MP3 files don't really have any
110 * This test was adapted from SDL_mixer. 109 * magic header we can check for. The MP3 player is expected to just
110 * pick the first thing that looks like a valid frame and start
111 * playing from there.
112 *
113 * So here's what we do: If the caller insists that this is really
114 * MP3 we'll take his word for it. Otherwise, use the same test as
115 * SDL_mixer does and check if the stream starts with something that
116 * looks like a frame.
117 *
118 * A frame begins with 11 bits of frame sync (all bits must be set),
119 * followed by a two-bit MPEG Audio version ID:
120 *
121 * 00 - MPEG Version 2.5 (later extension of MPEG 2)
122 * 01 - reserved
123 * 10 - MPEG Version 2 (ISO/IEC 13818-3)
124 * 11 - MPEG Version 1 (ISO/IEC 11172-3)
125 *
126 * Apparently we don't handle MPEG Version 2.5.
111 */ 127 */
112 if (SDL_RWread(internal->rw, mp3_magic, sizeof (mp3_magic), 1) != 1) 128 if (__Sound_strcasecmp(ext, "MP3") != 0)
113 { 129 {
114 Sound_SetError("MP3: Could not read MP3 magic."); 130 Uint8 mp3_magic[2];
115 return(0); 131
116 } 132 if (SDL_RWread(internal->rw, mp3_magic, sizeof (mp3_magic), 1) != 1)
117 if (mp3_magic[0] != 0xFF || (mp3_magic[1] & 0xF0) != 0xF0) 133 {
118 { 134 Sound_SetError("MP3: Could not read MP3 magic.");
119 Sound_SetError("MP3: Not an MP3 stream."); 135 return(0);
120 return(0); 136 } /*if */
121 } 137
122 SDL_RWseek(internal->rw, -sizeof (mp3_magic), SEEK_CUR); 138 if (mp3_magic[0] != 0xFF || (mp3_magic[1] & 0xF0) != 0xF0)
139 {
140 Sound_SetError("MP3: Not an MP3 stream.");
141 return(0);
142 } /* if */
143
144 /* !!! FIXME: If the seek fails, we'll probably miss a frame */
145 SDL_RWseek(internal->rw, -sizeof (mp3_magic), SEEK_CUR);
146 } /* if */
123 147
124 refCounter = RWops_RWRefCounter_new(internal->rw); 148 refCounter = RWops_RWRefCounter_new(internal->rw);
125 if (refCounter == NULL) 149 if (refCounter == NULL)
126 { 150 {
127 SNDDBG(("MP3: Failed to create reference counting RWops.\n")); 151 SNDDBG(("MP3: Failed to create reference counting RWops.\n"));
169 SMPEG_enablevideo(smpeg, 0); 193 SMPEG_enablevideo(smpeg, 0);
170 SMPEG_enableaudio(smpeg, 1); 194 SMPEG_enableaudio(smpeg, 1);
171 SMPEG_loop(smpeg, 0); 195 SMPEG_loop(smpeg, 0);
172 196
173 SMPEG_wantedSpec(smpeg, &spec); 197 SMPEG_wantedSpec(smpeg, &spec);
198
174 /* 199 /*
175 * One of the MP3:s I tried wouldn't work unless I added this line 200 * One of the MP3s I tried wouldn't work unless I added this line
176 * to tell SMPEG that yes, it may have the spec it wants. 201 * to tell SMPEG that yes, it may have the spec it wants.
177 */ 202 */
178 SMPEG_actualSpec(smpeg, &spec); 203 SMPEG_actualSpec(smpeg, &spec);
179 sample->actual.format = spec.format; 204 sample->actual.format = spec.format;
180 sample->actual.rate = spec.freq; 205 sample->actual.rate = spec.freq;