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Clean up a long comment about the ALAC data structures.

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This commit is contained in:
Mike Brady
2022-06-19 13:04:05 +01:00
parent 8c1bc87463
commit 2260853ebc
1 changed files with 59 additions and 57 deletions
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player.c
+59 -57
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@@ -249,82 +249,84 @@ int audio_packet_decode(short *dest, int *destlen, uint8_t *buf, int len, rtsp_c
static int init_alac_decoder(int32_t fmtp[12], rtsp_conn_info *conn) {
// clang-format off
// This is a guess, but the format of the fmtp looks identical to the format of an
// ALACSpecificCOnfig
// which is detailed in the file ALACMagicCookieDescription.txt in the Apple ALAC sample
// implementation
// ALACSpecificCOnfig which is detailed in the file ALACMagicCookieDescription.txt
// in the Apple ALAC sample implementation
// Here it is:
/*
struct ALACSpecificConfig (defined in ALACAudioTypes.h)
abstract This struct is used to describe codec provided information about the encoded
Apple Lossless bitstream.
It must accompany the encoded stream in the containing audio file and be provided
to the decoder.
field frameLength uint32_t indicating the frames per packet
when
no
explicit
frames per packet setting is
present in the packet header. The
encoder frames per packet can be explicitly set
but for maximum compatibility, the
default encoder setting of 4096 should be used.
* ALAC Specific Info (24 bytes) (mandatory)
__________________________________________________________________________________________________________________________________
field compatibleVersion uint8_t indicating compatible version,
The Apple Lossless codec stores specific information about the encoded stream in the ALACSpecificConfig. This
info is vended by the encoder and is used to setup the decoder for a given encoded bitstream.
When read from and written to a file, the fields of this struct must be in big-endian order.
When vended by the encoder (and received by the decoder) the struct values will be in big-endian order.
struct ALACSpecificConfig (defined in ALACAudioTypes.h)
abstract This struct is used to describe codec provided information about the encoded Apple Lossless bitstream.
It must accompany the encoded stream in the containing audio file and be provided to the decoder.
field frameLength uint32_t indicating the frames per packet when no explicit frames per packet setting is
present in the packet header. The encoder frames per packet can be explicitly set
but for maximum compatibility, the default encoder setting of 4096 should be used.
field compatibleVersion uint8_t indicating compatible version,
value must be set to 0
field bitDepth uint8_t describes the bit depth of the
source
PCM
data
(maximum
value = 32)
field bitDepth uint8_t describes the bit depth of the source PCM data (maximum value = 32)
field pb uint8_t currently unused tuning
parametetbugr.
field pb uint8_t currently unused tuning parameter.
value should be set to 40
field mb uint8_t currently unused tuning parameter.
value should be set to 14
field kb uint8_t currently unused tuning parameter.
field mb uint8_t currently unused tuning parameter.
value should be set to 10
field numChannels uint8_t describes the channel count (1 =
mono,
2
=
stereo,
etc...)
when channel layout info is not provided
in the 'magic cookie', a channel count > 2
describes a set of discreet channels
with no specific ordering
field kb uint8_t currently unused tuning parameter.
value should be set to 14
field maxRun uint16_t currently unused.
value should be set to 255
field numChannels uint8_t describes the channel count (1 = mono, 2 = stereo, etc...)
when channel layout info is not provided in the 'magic cookie', a channel count > 2
describes a set of discreet channels with no specific ordering
field maxFrameBytes uint32_t the maximum size of an Apple
Lossless
packet
within
the encoded stream.
value of 0 indicates unknown
field maxRun uint16_t currently unused.
value should be set to 255
field avgBitRate uint32_t the average bit rate in bits per
second
of
the
Apple
Lossless stream.
value of 0 indicates unknown
field maxFrameBytes uint32_t the maximum size of an Apple Lossless packet within the encoded stream.
value of 0 indicates unknown
field avgBitRate uint32_t the average bit rate in bits per second of the Apple Lossless stream.
value of 0 indicates unknown
field sampleRate uint32_t sample rate of the encoded stream
typedef struct ALACSpecificConfig
{
uint32_t frameLength;
uint8_t compatibleVersion;
uint8_t bitDepth;
uint8_t pb;
uint8_t mb;
uint8_t kb;
uint8_t numChannels;
uint16_t maxRun;
uint32_t maxFrameBytes;
uint32_t avgBitRate;
uint32_t sampleRate;
} ALACSpecificConfig;
field sampleRate uint32_t sample rate of the encoded stream
*/
// We are going to go on that basis
// We are going to go on that basis
// clang-format on
alac_file *alac;