=== 📡 Data Stream Payload Block (`DSPL`)

This block contains a generic data stream payload. Can be used for data streams such as bitstreams or flux data.
Each `DataStreamPayloadBlock` stores a compressed or uncompressed stream of binary data of variable length.
The block may be compressed using LZMA compression if compression is enabled for the image.

For flux captures, the payload data consists of:
* Data buffer: Raw flux transition timing data
* Index buffer: Index structure mapping logical positions to offsets within the data buffer

These two buffers are concatenated: `[data_buffer][index_buffer]` before compression and storage.
For other data types, the payload layout is specific to the data type.

==== Structure Definition

[source,c]
#define DATA_STREAM_PAYLOAD_MAGIC 0x4C505344
/** Data stream payload block header */
typedef struct DataStreamPayloadHeader
{
    uint32_t identifier;  ///< Block identifier, must be BlockType::DataStreamPayloadBlock (0x4C505344).
    uint16_t dataType;    ///< Data type classification (value from DataType), e.g., FluxData or BitstreamData.
    uint16_t compression; ///< Compression type (0 = None, 1 = Lzma).
    uint32_t cmpLength;   ///< Compressed length in bytes (includes LZMA properties if compressed).
    uint32_t length;      ///< Uncompressed length in bytes.
    uint64_t cmpCrc64;    ///< CRC64-ECMA checksum of the compressed payload (or same as crc64 if uncompressed).
    uint64_t crc64;       ///< CRC64-ECMA checksum of the uncompressed payload.
} DataStreamPayloadHeader;

==== Field Descriptions

[cols="2,2,2,6",options="header"]
|===
|Type
|Size
|Name
|Description

|uint32_t
|4 bytes
|identifier
|The data stream payload block identifier, always `DSPL` (`0x4C505344`)

|uint16_t
|2 bytes
|dataType
|The data type contained in this block (value from DataType), e.g., FluxData or BitstreamData. See Annex B.

|uint16_t
|2 bytes
|compression
|Compression type: 0 = None, 1 = Lzma

|uint32_t
|4 bytes
|cmpLength
|Total compressed payload size in bytes. For LZMA this includes the 5-byte properties prefix; see Appendix C.

|uint32_t
|4 bytes
|length
|Uncompressed length in bytes (for flux captures: total of data buffer + index buffer)

|uint64_t
|8 bytes
|cmpCrc64
|CRC64-ECMA of the compressed payload. For LZMA this covers the compressed stream only, excluding the 5-byte properties prefix; see Appendix C.

|uint64_t
|8 bytes
|crc64
|CRC64-ECMA checksum of the uncompressed payload data (for flux captures: data + index buffers)
|===

==== Payload Data

The payload data immediately follows the `DataStreamPayloadHeader`. If compression is Lzma, the first 5 bytes contain LZMA properties, followed by the compressed data. If compression is None, the payload data is stored uncompressed.

For flux captures, the uncompressed payload consists of:
* Data buffer: `length - indexOffset` bytes of flux transition timing data
* Index buffer: `indexOffset` bytes of index structure data

The `indexOffset` value from the corresponding `FluxEntry` indicates where the index buffer starts within the payload. For other data types, the payload layout is specific to the data type.