RiffExtractor.php

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<?php
class RiffExtractor {
    public static function findChunksFromFile( $filename, $maxChunks = -1 ) {
        $file = fopen( $filename, 'rb' );
        $info = self::findChunks( $file, $maxChunks );
        fclose( $file );
        return $info;
    }

    public static function findChunks( $file, $maxChunks = -1 ) {
        $riff = fread( $file, 4 );
        if ( $riff !== 'RIFF' ) {
            return false;
        }

        // Next four bytes are fileSize
        $fileSize = fread( $file, 4 );
        if ( !$fileSize || strlen( $fileSize ) != 4 ) {
            return false;
        }

        // Next four bytes are the FourCC
        $fourCC = fread( $file, 4 );
        if ( !$fourCC || strlen( $fourCC ) != 4 ) {
            return false;
        }

        // Create basic info structure
        $info = [
            'fileSize' => self::extractUInt32( $fileSize ),
            'fourCC' => $fourCC,
            'chunks' => [],
        ];
        $numberOfChunks = 0;

        // Find out the chunks
        while ( !feof( $file ) && !( $numberOfChunks >= $maxChunks && $maxChunks >= 0 ) ) {
            $chunkStart = ftell( $file );

            $chunkFourCC = fread( $file, 4 );
            if ( !$chunkFourCC || strlen( $chunkFourCC ) != 4 ) {
                return $info;
            }

            $chunkSize = fread( $file, 4 );
            if ( !$chunkSize || strlen( $chunkSize ) != 4 ) {
                return $info;
            }
            $intChunkSize = self::extractUInt32( $chunkSize );

            // Add chunk info to the info structure
            $info['chunks'][] = [
                'fourCC' => $chunkFourCC,
                'start' => $chunkStart,
                'size' => $intChunkSize
            ];

            // Uneven chunks have padding bytes
            $padding = $intChunkSize % 2;
            // Seek to the next chunk
            fseek( $file, $intChunkSize + $padding, SEEK_CUR );

        }

        return $info;
    }

    public static function extractUInt32( $string ) {
        return unpack( 'V', $string )[1];
    }
};