The SDI receiver has a 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 determines the transport format by looking only 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 work with identical timing to corresponding interlaced formats. This means the receiver cannot distinguish interlaced formats by examining the timing. The transport format detection function reports PsF video formats as interlaced formats (rx_t_scan is Low). Your application must examine the ST 352 payload ID packets to discover whether the actual video format is PsF or interlaced.
The 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 Table: 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.
The transport detector also determines the frame rate of the transport signal. This feature is dependent on the rx_bit_rate input in HD-SDI and 3G-SDI modes to distinguish between integer and non-integer frame rates. The rx_t_rate port indicates the frame rate of the transport signal as shown in Table: Frame Rate Encoding The encoding of the frame rate matches the encoding used in the picture rate field of SMPTE ST 352 payload ID packets. However, rx_t_rate shows the transport frame rate, not the picture rate. Also, the rx_t_rate port value is always the frame rate, even for interlaced transports.