A digital data transmitting apparatus including a reproducing device classifies serial packet data that are read at a variable rate from a digital data medium and demodulates into at least picture data, audio data and other data, an MPEG transport stream (MPEG-TS) generating device generates an MPEG-TS based on the digital data, and a digital interface device converts the generated MPEG-TS into digital transmission data and transmits the digital transmission data at a predetermined transmission rate. A digital data receiving apparatus including a digital interface device is operable at a predetermined transmission rate, a digital data receiving device receives digital data via the digital interface device, an MPEG-TS reproducing device reproduces an MPEG-TS from the received digital data, a reproducing device classifies the reproduced MPEG-TS into at least picture data, audio data, and private data, and a control device controls the reproducing device based on the private data.