MPEG-1

Abstract: A method for ensuring synchronization of MPEG-1 data is carried in an MPEG-2 transport stream for decoding by an MPEG-1 decoder. The method includes searching the MPEG-2 transport stream for a packet start code prefix indicating the start of a PES packet and storing the data associated with the PES packet into a buffer. If the PES packet is a video PES packet, the packet header is examined to determine if a PTS is present. If a PTS is present, the video data in the PES packet are examined during storage to the buffer to locate the first occurrence of a picture start code in the data. Once the first occurrence of a picture start code is located, a flag is set indicating the correspondence between the PTS and the identified picture start code. The video data remaining in the video PES packet is then stored to the buffer without further examination. The PES packet data are stored without examination if a PTS is not present. In either instance, the stored data are transmitted from the buffer to the video decoder in known lengths. If the PES packet is an audio PES packet, a current value of a system time clock is subtracted from a value of a first PTS contained in an audio PES packet to calculate an audio delay. The audio delay is then adjusted to account for audio decoding, audio transmission, and video decoding times. Audio data stored in the buffer are not enabled for delivery to an audio decoder until after the audio delay has elapsed.

Abstract: We introduce the concept of dynamic rate shaping, a technique to adapt the rate of compressed video bitstreams (MPEG-1, MPEG-2, H.261, as well as JPEG) to dynamically varying bit rate constraints. The approach provides an interface (or filter) between the encoder and the network, with which the encoder's output can be perfectly matched to the network's quality of service characteristics. Since the presented algorithms do not require interaction with the encoder, they are fully applicable to precoded, stored video (e.g., video-on-demand systems). By decoupling the encoder and the network, universal interoperability can be achieved. In essence, DRS bridges the gap between CBR and VBR video, allowing a continuum of possibilities between the two. A set of low-complexity algorithms for so-called unconstrained dynamic rate shaping are presented, and both optimal and extremely fast designs are discussed. Experimental results are provided using actual MPEG-2 bitstreams.

Abstract: A method for real-time transcoding of MPEG-2 video bit streams is presented that can be applied at different levels of complexity. The proposed method has been developed in the ACTS ATLANTIC project. It is based on the following elements: - Reuse of motion vectors and coding mode decisions carried in the input bit stream. - Modelling of the impairments already present in the input. - Use of bit rate statistics from the input bit stream. Experimental results confirm that high picture quality can be maintained. Furthermore, the proposed elements and transcoding algorithms are not limited to MPEG-2 and can be extended to a generic transcoding method suitable for the common standards JPEG, H.263, MPEG-1 and MPEG-2 alike.