Sound Archives (.snd)

Sound archives store DOOM: Eternal and DOOM: The Dark Ages audio files (samples).

File Format

// Eternal version of sndEntry
struct sndEntry_Eternal
{
	uint64_t farmhash;    // Farmhash64 of the entry's DECODED data
    uint32_t sampleID;    // ID used to to reference this sample in the sound banks
    uint32_t encodedSize; // Size of the entry's data as it's stored in the archive.
    uint64_t offset;      // Location of entry's data in the file. Relative to beginning of file
    uint32_t decodedSize; // Size of the entry's data after being decoded
    uint16_t encoding;    // Either 2 or 3
    uint16_t metaSize;    // Size of this entry's meta section inside the meta blob
    uint32_t metaOffset;  // Location of this entry's meta section. Relative to global offset 0xC
}

// Dark Ages version of sndEntry
struct sndEntry_DarkAges
{
	uint64_t farmhash;    // Farmhash64 of the entry's data
    uint32_t sampleID;    // ID used to to reference this sample in the sound banks
    uint32_t encodedSize; // Size of the entry's data as it's stored in the archive.
    uint64_t offset;      // Location of entry's data in the file. Relative to beginning of file
    uint32_t decodedSize; // Always equal to encodedSize
    uint32_t metaSize;    // Size of this entry's meta section inside the meta blob
    uint32_t metaOffset;  // Location of this entry's meta section. Relative to global offset 0xC
}

struct sndHeaderChunk
{
	uint32_t  metaSize;   // Size of the header chunk's meta blob + 4
    char*     metaBlob;   // Header chunk's meta blob. Length == metaSize - 4
    uint32_t  numEntries; // Number of entries
	sndEntry* entries;    // Array of entry information. Length == numEntries. Exact format depends on the game    
}

struct snd
{
	uint32_t version;    // Always 6
    uint32_t headerSize; // Size of the header chunk
    sndHeaderChunk;      // Header chunk. Exact size given by headerSize
    char* dataChunk;     // Data chunk. Stores the complete audio samples. Length == remainder of file
}

About: Meta Blob

Audio samples in both games use RIFF as their basic format. A sample's "meta" section consists of the start of the file, up to and including the length field of it's data chunk.

Code that demonstrates how to calculate the length of a sample's meta chunk can be found here