The SDI receiver has transport format detector function. This function examines the timing of the video signals in the SDI data streams and determines which video format is being received. The operation of this function is independent of and not dependent on the ST 352 payload ID packets. This function determines the transport format, not the picture format. Usually these are the same, but not always. For example, when 1080p 60 Hz video is transported on 3G-SDI level B-DL, the video transport is actually 1080i 60 Hz – the transport is interlaced, but the picture is progressive.
The transport format detection function makes it determination of the transport format purely by looking at the video timing. It cannot distinguish between video formats that have exactly the same timing. For example, progressive segmented frame (PsF) video formats are intentionally designed to with identical timing to corresponding interlaced formats and cannot be distinguished from interlaced formats by examining the timing. The transport format detection function reports PsF video formats as interlaced formats (rx_t_scan is Low). The user application must examine the ST 352 payload ID packets to discover whether the actual video format is PsF or interlaced.
6G-SDI and 12G-SDI mappings defined by SMPTE always subdivide the images into multiple sub-images. Each sub-image is formatted as a regular 1080p image. The transport format detection function examines the timing of data stream 1 (ds1) only. Thus, it reports the video transport of 6G-SDI and 12G-SDI signals as 1080p signals (rx_t_family = 0000 and rx_t_scan = 1).
The rx_t_family output port provides a 4-bit code that indicates the matching video format family. The encoding of this output port is shown in See Video Format Encoding. The transport detection function also determines whether or not the transport is interlaced or progressive and reports this on the rx_t_scan output port.