Added ID3v2 support for FLAC files. (Fixes #417) (#418)

* Added ID3v2 support for FLAC files.  (Fixes #417)

* Fix ID3v2 header size calculation, adjust ID3v2 logic for FLAC files

---------

Co-authored-by: Vanilagy <[email protected]>

src/flac/flac-demuxer.ts

@@ -37,6 +37,7 @@ import {
 	getSampleRateOrUncommon,
 } from './flac-misc';
 import { Bitstream } from '../../shared/bitstream';
+import { ID3_V2_HEADER_SIZE, parseId3V2Tag, readId3V2Header } from '../id3';
 
 type FlacAudioInfo = {
 	numberOfChannels: number;
@@ -102,9 +103,34 @@ export class FlacDemuxer extends Demuxer {
 	}
 
 	async readMetadata() {
-		let currentPos = 4; // Skip 'fLaC'
-
 		return (this.metadataPromise ??= (async () => {
+			// Read all ID3v2 tags at the start of the file
+			let currentPos = 0;
+			while (true) {
+				let headerSlice = this.reader.requestSlice(currentPos, ID3_V2_HEADER_SIZE);
+				if (headerSlice instanceof Promise) headerSlice = await headerSlice;
+
+				if (!headerSlice) {
+					this.lastSampleLoaded = true;
+					return;
+				}
+
+				const id3V2Header = readId3V2Header(headerSlice);
+				if (!id3V2Header) {
+					break;
+				}
+
+				let contentSlice = this.reader.requestSlice(headerSlice.filePos, id3V2Header.size);
+				if (contentSlice instanceof Promise) contentSlice = await contentSlice;
+				assert(contentSlice);
+
+				parseId3V2Tag(contentSlice, id3V2Header, this.metadataTags);
+
+				currentPos = headerSlice.filePos + id3V2Header.size;
+			}
+
+			currentPos += 4; // Skip 'fLaC'
+
 			while (
 				this.reader.fileSize === null
 				|| currentPos < this.reader.fileSize

src/id3.ts

@@ -152,7 +152,11 @@ export const readId3V2Header = (slice: FileSlice): Id3V2Header | null => {
 		return null;
 	}
 
-	const size = decodeSynchsafe(sizeRaw);
+	let size = decodeSynchsafe(sizeRaw);
+
+	if (flags & Id3V2HeaderFlags.Footer) {
+		size += ID3_V2_HEADER_SIZE;
+	}
 
 	return { majorVersion, revision, flags, size };
 };
@@ -165,12 +169,12 @@ export const parseId3V2Tag = (slice: FileSlice, header: Id3V2Header, tags: Metad
 		return;
 	}
 
-	const bytes = readBytes(slice, header.size);
-	const reader = new Id3V2Reader(header, bytes);
+	const dataSize = (header.flags & Id3V2HeaderFlags.Footer)
+		? header.size - ID3_V2_HEADER_SIZE
+		: header.size;
 
-	if (header.flags & Id3V2HeaderFlags.Footer) {
-		reader.removeFooter();
-	}
+	const bytes = readBytes(slice, dataSize);
+	const reader = new Id3V2Reader(header, bytes);
 
 	if ((header.flags & Id3V2HeaderFlags.Unsynchronisation) && header.majorVersion === 3) {
 		reader.ununsynchronizeAll();
@@ -463,11 +467,6 @@ export class Id3V2Reader {
 		this.view = new DataView(this.bytes.buffer);
 	}
 
-	removeFooter() {
-		this.bytes = this.bytes.subarray(0, this.bytes.length - ID3_V2_HEADER_SIZE);
-		this.view = new DataView(this.bytes.buffer);
-	}
-
 	readBytes(length: number) {
 		const slice = this.bytes.subarray(this.pos, this.pos + length);
 		this.pos += length;

src/input-format.ts

@@ -446,7 +446,23 @@ export class OggInputFormat extends InputFormat {
 export class FlacInputFormat extends InputFormat {
 	/** @internal */
 	async _canReadInput(input: Input) {
-		let slice = input._reader.requestSlice(0, 4);
+		let currentPos = 0;
+
+		// There might be ID3v2 headers at the start, skip 'em
+		while (true) {
+			let slice = input._reader.requestSlice(currentPos, ID3_V2_HEADER_SIZE);
+			if (slice instanceof Promise) slice = await slice;
+			if (!slice) break;
+
+			const id3V2Header = readId3V2Header(slice);
+			if (!id3V2Header) {
+				break;
+			}
+
+			currentPos = slice.filePos + id3V2Header.size;
+		}
+
+		let slice = input._reader.requestSlice(currentPos, 4);
 		if (slice instanceof Promise) slice = await slice;
 		if (!slice) return false;
 

src/metadata.ts

@@ -20,7 +20,8 @@ import { isRecordStringString } from './misc';
  * in Vorbis-style comment headers.
  * - For WAVE files, the metadata refers to the chunks within the RIFF INFO chunk.
  * - For ADTS files, the metadata refers to the ID3v2 tags.
- * - For FLAC files, the metadata lives in Vorbis style in the Vorbis comment block.
+ * - For FLAC files, the metadata lives in Vorbis style in the Vorbis comment block, or sometimes in ID3v2 tags at the
+ * start of the file.
  * - For MPEG-TS files, metadata tags are currently not supported.
  *
  * @group Metadata tags
@@ -78,7 +79,8 @@ export type MetadataTags = {
 	 * Additionally, the `'vendor'` key refers to the vendor string within this header.
 	 * - WAVE: The individual metadata chunks within the RIFF INFO chunk. Values are always ISO 8859-1 strings.
 	 * - FLAC: The key-value string pairs from the vorbis metadata block (see RFC 9639, Section D.2.3).
-	 * Additionally, the `'vendor'` key refers to the vendor string within this header.
+	 * Additionally, the `'vendor'` key refers to the vendor string within this header. If ID3v2 tags appear at the
+	 * start of the file, their content is stored just like for MP3.
 	 * - MPEG-TS: Not supported.
 	*/
 	raw?: Record<string, string | Uint8Array | RichImageData | AttachedFile | Record<string, string> | null>;