loosen dependencies over mpegaudiodec

Originally committed as revision 9080 to svn://svn.ffmpeg.org/ffmpeg/trunk
2025-12-24 11:52:06 +08:00 · 2007-05-20 13:40:07 +00:00
parent 663deb54af
commit 4bd8e17c8d
7 changed files with 234 additions and 155 deletions
--- a/libavcodec/mpegaudiodecheader.c
+++ b/libavcodec/mpegaudiodecheader.c
@@ -0,0 +1,109 @@
+/*
+ * MPEG Audio header decoder
+ * Copyright (c) 2001, 2002 Fabrice Bellard.
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file mpegaudiodecheader.c
+ * MPEG Audio header decoder.
+ */
+
+//#define DEBUG
+#include "avcodec.h"
+#include "mpegaudio.h"
+#include "mpegaudiodata.h"
+
+
+int decode_header(MPADecodeContext *s, uint32_t header)
+{
+    int sample_rate, frame_size, mpeg25, padding;
+    int sample_rate_index, bitrate_index;
+    if (header & (1<<20)) {
+        s->lsf = (header & (1<<19)) ? 0 : 1;
+        mpeg25 = 0;
+    } else {
+        s->lsf = 1;
+        mpeg25 = 1;
+    }
+
+    s->layer = 4 - ((header >> 17) & 3);
+    /* extract frequency */
+    sample_rate_index = (header >> 10) & 3;
+    sample_rate = ff_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25);
+    sample_rate_index += 3 * (s->lsf + mpeg25);
+    s->sample_rate_index = sample_rate_index;
+    s->error_protection = ((header >> 16) & 1) ^ 1;
+    s->sample_rate = sample_rate;
+
+    bitrate_index = (header >> 12) & 0xf;
+    padding = (header >> 9) & 1;
+    //extension = (header >> 8) & 1;
+    s->mode = (header >> 6) & 3;
+    s->mode_ext = (header >> 4) & 3;
+    //copyright = (header >> 3) & 1;
+    //original = (header >> 2) & 1;
+    //emphasis = header & 3;
+
+    if (s->mode == MPA_MONO)
+        s->nb_channels = 1;
+    else
+        s->nb_channels = 2;
+
+    if (bitrate_index != 0) {
+        frame_size = ff_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index];
+        s->bit_rate = frame_size * 1000;
+        switch(s->layer) {
+        case 1:
+            frame_size = (frame_size * 12000) / sample_rate;
+            frame_size = (frame_size + padding) * 4;
+            break;
+        case 2:
+            frame_size = (frame_size * 144000) / sample_rate;
+            frame_size += padding;
+            break;
+        default:
+        case 3:
+            frame_size = (frame_size * 144000) / (sample_rate << s->lsf);
+            frame_size += padding;
+            break;
+        }
+        s->frame_size = frame_size;
+    } else {
+        /* if no frame size computed, signal it */
+        return 1;
+    }
+
+#if defined(DEBUG)
+    dprintf(s->avctx, "layer%d, %d Hz, %d kbits/s, ",
+           s->layer, s->sample_rate, s->bit_rate);
+    if (s->nb_channels == 2) {
+        if (s->layer == 3) {
+            if (s->mode_ext & MODE_EXT_MS_STEREO)
+                dprintf(s->avctx, "ms-");
+            if (s->mode_ext & MODE_EXT_I_STEREO)
+                dprintf(s->avctx, "i-");
+        }
+        dprintf(s->avctx, "stereo");
+    } else {
+        dprintf(s->avctx, "mono");
+    }
+    dprintf(s->avctx, "\n");
+#endif
+    return 0;
+}