src/webm-writer-0.2.0.js
function writeEBML(buffer, bufferFileOffset, ebml) {
            // Is the ebml an array of sibling elements?
            if (Array.isArray(ebml)) {
                for (var i = 0; i < ebml.length; i++) {
                    writeEBML(buffer, bufferFileOffset, ebml[i]);
                }
            // Is this some sort of raw data that we want to write directly?
            } else if (typeof ebml === "string") {
                buffer.writeString(ebml);
            } else if (ebml instanceof Uint8Array) {
                buffer.writeBytes(ebml);
            } else if (ebml.id){
                // We're writing an EBML element
                ebml.offset = buffer.pos + bufferFileOffset;
                
                buffer.writeUnsignedIntBE(ebml.id); // ID field
                
                // Now we need to write the size field, so we must know the payload size:
                
                if (Array.isArray(ebml.data)) {
                    // Writing an array of child elements. We won't try to measure the size of the children up-front
                    
                    var
                        sizePos, dataBegin, dataEnd;
                    
                    if (ebml.size === -1) {
                        // Write the reserved all-one-bits marker to note that the size of this element is unknown/unbounded
                        buffer.writeByte(0xFF);
                    } else {
                        sizePos = buffer.pos;
                        
                        /* Write a dummy size field to overwrite later. 4 bytes allows an element maximum size of 256MB,
                         * which should be plenty (we don't want to have to buffer that much data in memory at one time
                         * anyway!)
                         */
                        buffer.writeBytes([0, 0, 0, 0]);
                    }
                    
                    dataBegin = buffer.pos;
                    
                    ebml.dataOffset = dataBegin + bufferFileOffset;
                    writeEBML(buffer, bufferFileOffset, ebml.data);
                    
                    if (ebml.size !== -1) {
                        dataEnd = buffer.pos;
                        
                        ebml.size = dataEnd - dataBegin;
                        
                        buffer.seek(sizePos);
                        buffer.writeEBMLVarIntWidth(ebml.size, 4); // Size field
                        
                        buffer.seek(dataEnd);
                    }
                } else if (typeof ebml.data === "string") {
                    buffer.writeEBMLVarInt(ebml.data.length); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeString(ebml.data);
                } else if (typeof ebml.data === "number") {
                    // Allow the caller to explicitly choose the size if they wish by supplying a size field
                    if (!ebml.size) {
                        ebml.size = buffer.measureUnsignedInt(ebml.data);
                    }
                    
                    buffer.writeEBMLVarInt(ebml.size); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeUnsignedIntBE(ebml.data, ebml.size);
                } else if (ebml.data instanceof EBMLFloat64) {
                    buffer.writeEBMLVarInt(8); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeDoubleBE(ebml.data.value);
                } else if (ebml.data instanceof EBMLFloat32) {
                    buffer.writeEBMLVarInt(4); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeFloatBE(ebml.data.value);
                } else if (ebml.data instanceof Uint8Array) {
                    buffer.writeEBMLVarInt(ebml.data.byteLength); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeBytes(ebml.data);
                } else {
                    throw "Bad EBML datatype " + typeof ebml.data;
                }
            } else {
                throw "Bad EBML datatype " + typeof ebml.data;
            }
        }
function writeEBML(buffer, bufferFileOffset, ebml) {
            // Is the ebml an array of sibling elements?
            if (Array.isArray(ebml)) {
                for (var i = 0; i < ebml.length; i++) {
                    writeEBML(buffer, bufferFileOffset, ebml[i]);
                }
            // Is this some sort of raw data that we want to write directly?
            } else if (typeof ebml === "string") {
                buffer.writeString(ebml);
            } else if (ebml instanceof Uint8Array) {
                buffer.writeBytes(ebml);
            } else if (ebml.id){
                // We're writing an EBML element
                ebml.offset = buffer.pos + bufferFileOffset;
                
                buffer.writeUnsignedIntBE(ebml.id); // ID field
                
                // Now we need to write the size field, so we must know the payload size:
                
                if (Array.isArray(ebml.data)) {
                    // Writing an array of child elements. We won't try to measure the size of the children up-front
                    
                    var
                        sizePos, dataBegin, dataEnd;
                    
                    if (ebml.size === -1) {
                        // Write the reserved all-one-bits marker to note that the size of this element is unknown/unbounded
                        buffer.writeByte(0xFF);
                    } else {
                        sizePos = buffer.pos;
                        
                        /* Write a dummy size field to overwrite later. 4 bytes allows an element maximum size of 256MB,
                         * which should be plenty (we don't want to have to buffer that much data in memory at one time
                         * anyway!)
                         */
                        buffer.writeBytes([0, 0, 0, 0]);
                    }
                    
                    dataBegin = buffer.pos;
                    
                    ebml.dataOffset = dataBegin + bufferFileOffset;
                    writeEBML(buffer, bufferFileOffset, ebml.data);
                    
                    if (ebml.size !== -1) {
                        dataEnd = buffer.pos;
                        
                        ebml.size = dataEnd - dataBegin;
                        
                        buffer.seek(sizePos);
                        buffer.writeEBMLVarIntWidth(ebml.size, 4); // Size field
                        
                        buffer.seek(dataEnd);
                    }
                } else if (typeof ebml.data === "string") {
                    buffer.writeEBMLVarInt(ebml.data.length); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeString(ebml.data);
                } else if (typeof ebml.data === "number") {
                    // Allow the caller to explicitly choose the size if they wish by supplying a size field
                    if (!ebml.size) {
                        ebml.size = buffer.measureUnsignedInt(ebml.data);
                    }
                    
                    buffer.writeEBMLVarInt(ebml.size); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeUnsignedIntBE(ebml.data, ebml.size);
                } else if (ebml.data instanceof EBMLFloat64) {
                    buffer.writeEBMLVarInt(8); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeDoubleBE(ebml.data.value);
                } else if (ebml.data instanceof EBMLFloat32) {
                    buffer.writeEBMLVarInt(4); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeFloatBE(ebml.data.value);
                } else if (ebml.data instanceof Uint8Array) {
                    buffer.writeEBMLVarInt(ebml.data.byteLength); // Size field
                    ebml.dataOffset = buffer.pos + bufferFileOffset;
                    buffer.writeBytes(ebml.data);
                } else {
                    throw "Bad EBML datatype " + typeof ebml.data;
                }
            } else {
                throw "Bad EBML datatype " + typeof ebml.data;
            }
        }
function writeEBML ( buffer , bufferFileOffset , ebml ) { // Is the ebml an array of sibling elements? if ( Array . isArray ( ebml ) ) { for ( var i = 0 ; i < ebml . length ; i ++ ) { writeEBML ( buffer , bufferFileOffset , ebml [ i ] ) ; } // Is this some sort of raw data that we want to write directly? } else if ( typeof ebml === "string" ) { buffer . writeString ( ebml ) ; } else if ( ebml instanceof Uint8Array ) { buffer . writeBytes ( ebml ) ; } else if ( ebml . id ) { // We're writing an EBML element ebml . offset = buffer . pos + bufferFileOffset ; buffer . writeUnsignedIntBE ( ebml . id ) ; // ID field // Now we need to write the size field, so we must know the payload size: if ( Array . isArray ( ebml . data ) ) { // Writing an array of child elements. We won't try to measure the size of the children up-front var sizePos , dataBegin , dataEnd ; if ( ebml . size === - 1 ) { // Write the reserved all-one-bits marker to note that the size of this element is unknown/unbounded buffer . writeByte ( 0xFF ) ; } else { sizePos = buffer . pos ; /* Write a dummy size field to overwrite later. 4 bytes allows an element maximum size of 256MB,
                         * which should be plenty (we don't want to have to buffer that much data in memory at one time
                         * anyway!)
                         */ buffer . writeBytes ( [ 0 , 0 , 0 , 0 ] ) ; } dataBegin = buffer . pos ; ebml . dataOffset = dataBegin + bufferFileOffset ; writeEBML ( buffer , bufferFileOffset , ebml . data ) ; if ( ebml . size !== - 1 ) { dataEnd = buffer . pos ; ebml . size = dataEnd - dataBegin ; buffer . seek ( sizePos ) ; buffer . writeEBMLVarIntWidth ( ebml . size , 4 ) ; // Size field buffer . seek ( dataEnd ) ; } } else if ( typeof ebml . data === "string" ) { buffer . writeEBMLVarInt ( ebml . data . length ) ; // Size field ebml . dataOffset = buffer . pos + bufferFileOffset ; buffer . writeString ( ebml . data ) ; } else if ( typeof ebml . data === "number" ) { // Allow the caller to explicitly choose the size if they wish by supplying a size field if ( ! ebml . size ) { ebml . size = buffer . measureUnsignedInt ( ebml . data ) ; } buffer . writeEBMLVarInt ( ebml . size ) ; // Size field ebml . dataOffset = buffer . pos + bufferFileOffset ; buffer . writeUnsignedIntBE ( ebml . data , ebml . size ) ; } else if ( ebml . data instanceof EBMLFloat64 ) { buffer . writeEBMLVarInt ( 8 ) ; // Size field ebml . dataOffset = buffer . pos + bufferFileOffset ; buffer . writeDoubleBE ( ebml . data . value ) ; } else if ( ebml . data instanceof EBMLFloat32 ) { buffer . writeEBMLVarInt ( 4 ) ; // Size field ebml . dataOffset = buffer . pos + bufferFileOffset ; buffer . writeFloatBE ( ebml . data . value ) ; } else if ( ebml . data instanceof Uint8Array ) { buffer . writeEBMLVarInt ( ebml . data . byteLength ) ; // Size field ebml . dataOffset = buffer . pos + bufferFileOffset ; buffer . writeBytes ( ebml . data ) ; } else { throw "Bad EBML datatype " + typeof ebml . data ; } } else { throw "Bad EBML datatype " + typeof ebml . data ; } }
Write the given EBML object to the provided ArrayBufferStream.

The buffer's first byte is at bufferFileOffset inside the video file. This is used to complete offset and
dataOffset fields in each EBML structure, indicating the file offset of the first byte of the EBML element and
its data payload.
Write the given EBML object to the provided ArrayBufferStream .