Thunderbolt

The Thunderbolt logo depicts lightning, not thunder! The trademark is registered to Intel.

MPEG-2

IEEE 1394, Standard for a High Performance Serial Bus.

Thunderbolt refers to a bidirectional interface designed by Intel (apparently in collaboration with Apple). The scheme is intended to connect a computer and its peripheral devices; it achieves a data rate of about 10 Gb/s in each direction, and drives cables up to 3 m. Thunderbolt links can be daisy-chained. DisplayPort predates Thunderbolt; nevertheless, DisplayPort (with a Mini DisplayPort connector) is a specialization of Thunderbolt in which – apart from a very low-speed reverse channel to implement DDC – the data flow is unidirectional. A Thunderbolt link is capable of carrying two uncompressed 1080p60 R’G’B’ signal sets. Data flow across Thunderbolt is organized into packets; data exchange is based upon the protocols of PCI Express (PCIe), a commodity computer interface.

Part 2, Systems, of the MPEG-2 specification defines two multiplexing schemes. An MPEG-2 program stream is a multiplexing scheme appropriate for one program stored on or conveyed across relatively error-free media; an MPEG-2 transport stream is a multiplexing scheme appropriate for one or more programs stored on or conveyed across relatively error-prone media. Both of these schemes are outlined in MPEG-2 storage and transport, on page 555. They are generally appropriate for distribution, but not for acquisition or production. (An exception is Sony’s MPEG IMX scheme for SD, whose I-B frame structure and fairly high data rate enable use in production.)

IEEE 1394 (FireWire, i.LINK)

In 1995, the IEEE standardized a general-purpose highspeed serial bus capable of connecting up to 63 devices in a tree-shaped network through point-to-point connections. The link conveys data across two shielded twisted pairs (STP), and operates at 100 Mb/s,

400 Mb/s, or 800 Mb/s. Each point-to-point segment is limited to 4.5 m; there is a limit of 72 m across the breadth of a network. Asynchronous and isochronous modes are provided; the latter accommodates realtime traffic. Apple computer refers to the interface by their trademark FireWire. Sony’s trademark is i.LINK.

Though not practical for uncompressed video, IEEE 1394 has performance and features that make it

IEC 61883-1, Consumer audio/video equipment – Digital interface – Part 1: General. See also parts 2 through 5.

http: hypertext transfer protocol

The playlist is an Extended M3U Playlist file, either an .m3u file encoded in US-ASCII or an .m3u8 file encoded in UTF-8.

gzip: Gnu zip, a lossless data compression technique

highly practical for compressed video streams, particularly DV.

The standard 6-pin connector provides power for peripheral devices. Sony commonly uses a 4-pin connector not compliant with the IEEE standard. A node may have either 4-pin or 6-pin connectors.

Power is absent from the 4-pin connector; many people find the 4-pin connector to be mechanically flimsy.

IEC has standardized the transmission of digital video over IEEE 1394. Video is digitized according to BT.601, then motion-JPEG coded (using the DV standard) at about 25 Mb/s; this is colloquially known as 1394/DV25 (or DV25-over-1394). DV coding has been adapted to 100 Mb/s for HD (DV100); a standard for DV100-over-1394 has been adopted by IEC.

HTTP live streaming (HLS)

Apple has introduced a streaming adaptation of the http protocol that was devised for the World Wide Web. The scheme has aspects of stream transfer and aspects of file transfer.

The server segments programs into a sequence of media files each having short playback duration, typically a small integer number of seconds, 10 or so. Typically, a segment is represented by several media files containing the same program material coded at different bit rates. Each media file is an MPEG-2 transport stream including a program association table (PAT) and a program mapping table (PMT); these alllow stream decoding to start at any segment without requiring access to any earlier segment.

The server also prepares a playlist (index) file that associates time offsets to a set of filenames (actually, URLs) of media files along with their associated bit rates and sequence numbers. The playlist file can be gzipcompressed.

The client establishes the bit rate that it expects to be sustained, then accesses the playlist file to establish the filenames of the content at the desired time and the desired bit rate. The client issues an http request for the named file, and plays it.

There is no predetermined bound on program length: The server is free to add additional media files, and