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Diffstat (limited to 'DOCS/OUTDATED-tech/realcodecs/audio-codecs.txt')
| -rw-r--r-- | DOCS/OUTDATED-tech/realcodecs/audio-codecs.txt | 155 |
1 files changed, 155 insertions, 0 deletions
diff --git a/DOCS/OUTDATED-tech/realcodecs/audio-codecs.txt b/DOCS/OUTDATED-tech/realcodecs/audio-codecs.txt new file mode 100644 index 0000000000..fd28ab2a16 --- /dev/null +++ b/DOCS/OUTDATED-tech/realcodecs/audio-codecs.txt @@ -0,0 +1,155 @@ +all audio codecs (cook,atrk,14_4,28_8,dnet,sipr) have the same interface, +but i have only analyzed the cook codec + + +audio properties (hex) + +00 short text/description of the format (bitrate, when to use) +01 bitrate (bits/s) //avg. bytes/sec output +02 ulong: ? + ulong: samples per second + ushort: bits/sample + ushort: number of channels +03 same as 02 //constant 2 +04 long description +05 constant 1 (always?) +06 ulong: block align (input frame size for RADecode) +07 string: minimum player version +08 n/a +09 n/a +0A n/a +0B n/a +0C n/a +0D ? +0E ? leaf size +0F ? +10 ? +11 ? +12 ? +13 min. output buffer size? max. number of samples? +14 ? + + + + +functions: + +ulong result=RAOpenCodec2(ra_main_t *raMain); + +ulong result=RAInitDecoder(ra_main_t *raMain, ra_init_struct *raInit); +struct ra_init_struct { + ulong sample_rate; + ushort bits_per_sample; // unused by RAInitDecoder + ushort number_of_channels; + ushort unknown1; // 0 + ushort unknown2; // also unused (100) + ulong leaf_size; // leaf size (used for interleaving, but + // exists in audio stream description header (ASDH)) + ulong block_align; // packet size + ulong bits_per_sample; // unused (always 16) + char *ext_data; // 16 bytes located at the end of the + // ASDH +}; + +There are some information missing that you usually need for playback, +like bits per sample (the fileds aren't read by RAInitDecoder()). These +are hard coded in the "flavors", i.e. the sub formats. A flavor is an entry +in the list of available format variations like bitrate, number of channels, +decoding algorithm, and so on.We can get those information with the +following command: + + + +void *GetRAFlavorProperty(ra_main_t *raMain, ulong flavor, ulong property, + short *property_length_in_bytes); +returns property data for a specific data + +This is not important, because it's just a read only function. +These flavor properties don't seem to exist in + + +ulong RADecode(ra_main_t *raMain, char *input_buffer, + ulong input_buffer_size, char *output_buffer, + ulong *decoded_bytes, ulong p6=-1); + +RAFreeDecoder(ra_main_t *); + +RACloseCodec(ra_main_t *); + + +ulong RASetFlavor(ra_main_t *ra_main, ulong flavor); + +Set the flavor of the stream. + +a flavor is an entry in the list of available format variations like +bitrate, number of channels, decoding algorithm, and so on + + +audio data storage: +------------------- + +With Real Audio V5 (or earlier?), the audio streams can be interleaved, +i.e. the stream is striped amongst several data packets. The packets +(which have a fixed size packet_len) are split up into a fixed number +of num_parts equally sized parts - I call them leaves in lack of +better name. The leaves have the size leaf_size = packet_len / num_parts. + +To create a bunch of packets, you need 2*num_parts stream packets. +The first part of the first stream packet is stored in leaf number 0, +the first part of the second into leaf number num_parts, the one of the +next one into leaf number 1 etc. The following part of a stream packet +is stored 2*num_packets behind the current part of the same stream packet. + +In short words: when you have a matrix with the leaves as the values, +it's a transposition in conjunction with a permutation. + +packet | leaf | stream packet, part no. +-------+---------------+------------------------ +0 | 0 | (0,0) +0 | 1 | (2,0) +. | . | . +. | . | . +0 | num_parts-1 | (2*num_parts-2,0) +0 | num_parts | (1,0) +0 | num_parts+1 | (3,0) +. | . | . +. | . | . +0 | 2*num_parts-1 | (2*num_parts-1,0) +1 | 0 | (0,1) +. | . | . +. | . | . + + +sequence of calls: +------------------ + +RAOpenCodec2() + +RAInitDecoder() + +RASetFlavor() + +RAGetFlavorProperty(0xE) + +sequence of RADecode()s + +once a RAGetFlavorProperty(0xE) after some RADecode()s + +and occasionally the following sequence: +RAGetFlavorProperty(0) +RAGetFlavorProperty(7) +which is rather pointless because they only return +cleartext audio descriptions + +RAFreeDecoder() + +RACloseCodec() + + + +RAFlush(ra_main_t *raMain, char *output_buffer, ulong *retval) +will be called when seeking +output_buffer points to the output buffer from the last +decode operation. +retval is unknown, returning always 0x18 in a specific sample +-> further investigation needed |