diff options
| -rw-r--r-- | gst/mpegaudioparse/gstmp3types.c | 174 |
1 files changed, 147 insertions, 27 deletions
diff --git a/gst/mpegaudioparse/gstmp3types.c b/gst/mpegaudioparse/gstmp3types.c index d02ac867..30a4a7ff 100644 --- a/gst/mpegaudioparse/gstmp3types.c +++ b/gst/mpegaudioparse/gstmp3types.c @@ -22,9 +22,11 @@ #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/x-mp3", "audio/x-mp3", ".mp3 .mp2 .mp1 .mpga", mp3_type_find }, + { "mp3types_stream_audio/x-mp3", "audio/x-mp3", ".mp3 .mp2 .mp1 .mpga", mp3_type_find_stream }, { NULL, NULL, NULL, NULL }, }; @@ -46,38 +48,35 @@ mp3_type_find(GstBuffer *buf, gpointer private) data[0] == 'T' && data[1] == 'A' && data[2] == 'G') { /* ID V1 tags */ data += 128; + size -= 128; GST_DEBUG (0, "mp3typefind: detected ID3 Tag V1"); - } - else { - if (size >= 10 && + } 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); - - if (data[0] == 'I') { - /* ID3V2 */ - /* footer present? */ - if (data[5] & 0x10) - skip += 10; - - skip += 10; - } - - GST_DEBUG (0, "mp3typefind: detected ID3 Tag V2 with %u bytes", skip); - - /* we currently accept a valid ID3 tag as an mp3 as some ID3 tags have invalid - * offsets so the next check might fail */ - goto done; - } + { + 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 (0, "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) @@ -91,11 +90,132 @@ mp3_type_find(GstBuffer *buf, gpointer private) if (((head >> 10) & 0x3) == 0x3) return NULL; -done: caps = gst_caps_new ("mp3_type_find", "audio/x-mp3", NULL); 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 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 (0, "Calculated mad frame length of %u bytes", length); + GST_DEBUG (0, "samplerate = %lu - bitrate = %lu - layer = %lu - version = %lu", samplerate, bitrate, layer, version); + 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; + + data = GST_BUFFER_DATA (buf); + size = GST_BUFFER_SIZE (buf); + + while (size >= 4) { + head = GUINT32_FROM_BE(*((guint32 *)data)); + if ((head & 0xffe00000) == 0xffe00000) { + guint pos = 0; + guint length; + guint found = 0; /* number of valid headers found */ + do { + if ((length = mp3_type_frame_length_from_header (head))) { + pos += length; + found++; + if (pos + 4 >= size) { + if (found >= GST_MP3_TYPEFIND_MIN_HEADERS) + goto success; + } + head = GUINT32_FROM_BE(*((guint32 *) &(data[pos]))); + if ((head & 0xffe00000) != 0xffe00000) + break; + } else { + break; + } + } while (TRUE); + } + data++; + size--; + } + + return NULL; + +success: + return gst_caps_new ("mp3_type_find", "audio/x-mp3", NULL); +} static gboolean plugin_init (GModule *module, GstPlugin *plugin) |