FlacLoader: Parse SEEKTABLE header

Populates m_seektable attribute with FlacSeekPoints.

For more information see:
https://datatracker.ietf.org/doc/html/draft-ietf-cellar-flac#section-11.13

Co-authored-by: kleines Filmröllchen <filmroellchen@serenityos.org>

Userland/Libraries/LibAudio/FlacLoader.cpp

@@ -118,13 +118,20 @@ MaybeLoaderError FlacLoaderPlugin::parse_header()
     md5_checksum.bytes().copy_to({ m_md5_checksum, sizeof(m_md5_checksum) });
 
     // Parse other blocks
-    // TODO: For a simple first implementation, all other blocks are skipped as allowed by the FLAC specification.
-    // Especially the SEEKTABLE block may become useful in a more sophisticated version.
     [[maybe_unused]] u16 meta_blocks_parsed = 1;
     [[maybe_unused]] u16 total_meta_blocks = meta_blocks_parsed;
     FlacRawMetadataBlock block = streaminfo;
     while (!block.is_last_block) {
         block = TRY(next_meta_block(*bit_input));
+        switch (block.type) {
+        case (FlacMetadataBlockType::SEEKTABLE):
+            TRY(load_seektable(block));
+            break;
+        default:
+            // TODO: Parse the remaining metadata block types.
+            //       Currently only STREAMINFO and SEEKTABLE are handled.
+            break;
+        }
         ++total_meta_blocks;
     }
 
@@ -133,6 +140,21 @@ MaybeLoaderError FlacLoaderPlugin::parse_header()
     return {};
 }
 
+MaybeLoaderError FlacLoaderPlugin::load_seektable(FlacRawMetadataBlock& block)
+{
+    auto memory_stream = LOADER_TRY(Core::Stream::MemoryStream::construct(block.data.bytes()));
+    auto seektable_bytes = LOADER_TRY(BigEndianInputBitStream::construct(*memory_stream));
+    for (size_t i = 0; i < block.length / 18; ++i) {
+        FlacSeekPoint seekpoint {
+            .sample_index = LOADER_TRY(seektable_bytes->read_bits<u64>(64)),
+            .byte_offset = LOADER_TRY(seektable_bytes->read_bits<u64>(64)),
+            .num_samples = LOADER_TRY(seektable_bytes->read_bits<u16>(16))
+        };
+        m_seektable.append(seekpoint);
+    }
+    return {};
+}
+
 ErrorOr<FlacRawMetadataBlock, LoaderError> FlacLoaderPlugin::next_meta_block(BigEndianInputBitStream& bit_input)
 {
 

Userland/Libraries/LibAudio/FlacLoader.h

@@ -83,6 +83,7 @@ private:
     MaybeLoaderError decode_residual(Vector<i32>& decoded, FlacSubframeHeader& subframe, BigEndianInputBitStream& bit_input);
     // decode a single rice partition that has its own rice parameter
     ALWAYS_INLINE ErrorOr<Vector<i32>, LoaderError> decode_rice_partition(u8 partition_type, u32 partitions, u32 partition_index, FlacSubframeHeader& subframe, BigEndianInputBitStream& bit_input);
+    MaybeLoaderError load_seektable(FlacRawMetadataBlock&);
 
     // Converters for special coding used in frame headers
     ALWAYS_INLINE ErrorOr<u32, LoaderError> convert_sample_count_code(u8 sample_count_code);
@@ -113,6 +114,7 @@ private:
     // Whatever the last get_more_samples() call couldn't return gets stored here.
     Vector<Sample, FLAC_BUFFER_SIZE> m_unread_data;
     u64 m_current_sample_or_frame { 0 };
+    Vector<FlacSeekPoint> m_seektable;
 };
 
 }

Userland/Libraries/LibAudio/FlacTypes.h

@@ -87,4 +87,10 @@ struct FlacSubframeHeader {
     u8 bits_per_sample;
 };
 
+struct FlacSeekPoint {
+    u64 sample_index;
+    u64 byte_offset;
+    u16 num_samples;
+};
+
 }