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/* GStreamer
* Copyright (C) <1999> Erik Walthinsen <omega@cse.ogi.edu>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library 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
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/*#define DEBUG_ENABLED */
#include <gst/gst.h>
#include <string.h> /* memcmp */
static GstCaps* mp3_type_find(GstBuffer *buf, gpointer private);
static GstCaps* mp3_type_find_stream(GstBuffer *buf, gpointer private);
static GstTypeDefinition mp3type_definitions[] = {
{ "mp3types_audio/mpeg", "audio/mpeg", ".mp3 .mp2 .mp1 .mpga", mp3_type_find },
{ "mp3types_stream_audio/mpeg", "audio/mpeg", ".mp3 .mp2 .mp1 .mpga", mp3_type_find_stream },
{ NULL, NULL, NULL, NULL },
};
static GstCaps*
mp3_type_find(GstBuffer *buf, gpointer private)
{
guint8 *data;
gint size, layer;
guint32 head;
GstCaps *caps;
data = GST_BUFFER_DATA (buf);
size = GST_BUFFER_SIZE (buf);
GST_DEBUG ("mp3typefind: typefind");
/* gracefully ripped from libid3 */
if (size >= 3 &&
data[0] == 'T' && data[1] == 'A' && data[2] == 'G') {
/* ID V1 tags */
data += 128;
size -= 128;
GST_DEBUG ("mp3typefind: detected ID3 Tag V1");
} else if (size >= 10 &&
(data[0] == 'I' && data[1] == 'D' && data[2] == '3') &&
data[3] < 0xff && data[4] < 0xff &&
data[6] < 0x80 && data[7] < 0x80 && data[8] < 0x80 && data[9] < 0x80)
{
guint32 skip = 0;
skip = (skip << 7) | (data[6] & 0x7f);
skip = (skip << 7) | (data[7] & 0x7f);
skip = (skip << 7) | (data[8] & 0x7f);
skip = (skip << 7) | (data[9] & 0x7f);
/* include size of header */
skip += 10;
/* footer present? (only available since version 4) */
if (data[3] > 3 && (data[5] & 0x10))
skip += 10;
GST_DEBUG ("mp3typefind: detected ID3 Tag V2 with %u bytes", skip);
size -= skip;
data += skip;
}
if (size < 4)
return NULL;
/* now with the right postion, do typefinding */
head = GUINT32_FROM_BE(*((guint32 *)data));
if ((head & 0xffe00000) != 0xffe00000)
return NULL;
if (!(layer = ((head >> 17) & 3)))
return NULL;
layer = 4 - layer;
if (((head >> 12) & 0xf) == 0xf)
return NULL;
if (!((head >> 12) & 0xf))
return NULL;
if (((head >> 10) & 0x3) == 0x3)
return NULL;
caps = GST_CAPS_NEW ("mp3_type_find", "audio/mpeg", "layer", GST_PROPS_INT (layer));
return caps;
}
static guint mp3types_bitrates[2][3][16] =
{ { {0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, },
{0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, },
{0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, } },
{ {0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, },
{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, },
{0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, } },
};
static guint mp3types_freqs[3][3] =
{ {44100, 48000, 32000},
{22050, 24000, 16000},
{11025, 12000, 8000}};
static inline guint
mp3_type_frame_length_from_header (guint32 header, guint *put_layer)
{
guint length;
gulong samplerate, bitrate, layer, version;
/* we don't need extension, mode, copyright, original or emphasis for the frame length */
header >>= 9;
/* padding */
length = header & 0x1;
header >>= 1;
/* sampling frequency */
samplerate = header & 0x3;
if (samplerate == 3)
return 0;
header >>= 2;
/* bitrate index */
bitrate = header & 0xF;
if (bitrate == 15 || bitrate == 0)
return 0;
/* ignore error correction, too */
header >>= 5;
/* layer */
layer = 4 - (header & 0x3);
if (layer == 4)
return 0;
header >>= 2;
/* version */
version = header & 0x3;
if (version == 1)
return 0;
/* lookup */
bitrate = mp3types_bitrates[version == 3 ? 0 : 1][layer - 1][bitrate];
samplerate = mp3types_freqs[version > 0 ? version - 1 : 0][samplerate];
/* calculating */
if (layer == 1) {
length = ((12000 * bitrate / samplerate) + length) * 4;
} else {
length += ((layer == 3 && version == 0) ? 144000 : 72000) * bitrate / samplerate;
}
GST_DEBUG ("Calculated mad frame length of %u bytes", length);
GST_DEBUG ("samplerate = %lu - bitrate = %lu - layer = %lu - version = %lu", samplerate, bitrate, layer, version);
if (put_layer)
*put_layer = layer;
return length;
}
/* increase this value when this function finds too many false positives */
/**
* The chance that random data is identified as a valid mp3 header is 63 / 2^18
* (0.024%) per try. This makes the function for calculating false positives
* 1 - (1 - ((63 / 2 ^18) ^ GST_MP3_TYPEFIND_MIN_HEADERS)) ^ buffersize)
* This has the following probabilities of false positives:
* bufsize MIN_HEADERS
* (bytes) 1 2 3 4
* 4096 62.6% 0.02% 0% 0%
* 16384 98% 0.09% 0% 0%
* 1 MiB 100% 5.88% 0% 0%
* 1 GiB 100% 100% 1.44% 0%
* 1 TiB 100% 100% 100% 0.35%
* This means that the current choice (3 headers by most of the time 4096 byte
* buffers is pretty safe for now.
* It is however important to note that in a worst case example a buffer of size
* 1440 * GST_MP3_TYPEFIND_MIN_HEADERS + 3
* bytes is needed to reliable find the mp3 stream in a buffer when scanning
* starts at a random position. This is currently (4323 bytes) slightly above
* the default buffer size. But you rarely hit the worst case - average mp3
* frames are in the 500 bytes range.
*/
#define GST_MP3_TYPEFIND_MIN_HEADERS 3
static GstCaps*
mp3_type_find_stream (GstBuffer *buf, gpointer private)
{
guint8 *data;
guint size;
guint32 head;
gint layer = 0;
data = GST_BUFFER_DATA (buf);
size = GST_BUFFER_SIZE (buf);
while (size >= 4) {
head = GUINT32_FROM_BE(*((guint32 *)data));
if ((head & 0xffe00000) == 0xffe00000) {
guint length;
guint prev_layer = 0;
guint found = 0; /* number of valid headers found */
guint pos = 0;
do {
if ((length = mp3_type_frame_length_from_header (head, &layer))) {
if (prev_layer && prev_layer != layer)
break;
prev_layer = layer;
pos += length;
found++;
if (pos + 4 >= size) {
if (found >= GST_MP3_TYPEFIND_MIN_HEADERS) {
goto success;
} else {
break;
}
}
head = GUINT32_FROM_BE(*((guint32 *) &(data[pos])));
if ((head & 0xffe00000) != 0xffe00000)
break;
} else {
break;
}
} while (TRUE);
}
data++;
size--;
}
return NULL;
success:
g_assert (layer);
return GST_CAPS_NEW ("mp3_type_find", "audio/mpeg", "layer", GST_PROPS_INT (layer));
}
static gboolean
plugin_init (GModule *module, GstPlugin *plugin)
{
gint i=0;
while (mp3type_definitions[i].name) {
GstTypeFactory *type;
type = gst_type_factory_new (&mp3type_definitions[i]);
gst_plugin_add_feature (plugin, GST_PLUGIN_FEATURE (type));
i++;
}
/* gst_info("gsttypes: loaded %d mp3 types\n",i); */
return TRUE;
}
GstPluginDesc plugin_desc = {
GST_VERSION_MAJOR,
GST_VERSION_MINOR,
"mp3types",
plugin_init
};
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