8.3 Video timing

EIS defines the video timing formats tabulated below: four standard-definition (SD) and fourteen high-definition (HD) rasters. The three 1080-line formats at 50, 59.94, and 60 frames per second are listed because display equipment defaults to them; on an analog component interface at 148.5 MHz they are rare, and a port lists one only when it generates or locks to it.

A product's port list shall name, for each video sync input (COAX-IN) and output (COAX-OUT), every format of clause 8.3 the port accepts or generates, by its format ID (VID-001). A port may list one format or all of them. A COAX-THRU carries the formats of its COAX-IN, and a patch jack lists none (7.1). A format that is not in the table is listed under its own name, and EIS says nothing about it.

For each format a port lists, the video timing a product generates at a COAX-OUT, and the video timing it locks to at a COAX-IN, shall match the format's publication within the tolerances that publication states (VID-002). For a progressive format, and along the line for a high-definition interlaced format, the row below is that publication's raster, sample for sample. For the two standard-definition interlaced formats the row is the reference raster: the publication's figures in microseconds, with the digital active line placed as ITU-R BT.601 places it against the timing reference OH, 16 and 122 luminance samples for the 525-line system and 12 and 132 for the 625-line system.

Composite color encoding (NTSC or PAL) applies only to the interlaced SD formats. A component output (YPbPr, RGBS, RGSB, or RGBHV) may use any listed format. A port that locks to an external video sync takes the selected format; EIS does not require format conversion.

Formats

The tables are generated from data/video_timings.json, where each row cites its publication: SMPTE or ITU, and CTA-861 for the two progressive SD formats.

Progressive SD. 480p59.94 and 576p50 are the 720 × 480 and 720 × 576 progressive rasters CTA-861 tabulates (video format timings 2 and 3, and 17 and 18), the rasters display equipment accepts. SMPTE ST 293, with 483 active lines, and ITU-R BT.1358 are the production systems they descend from, not what the rows reproduce.

Sample clocks are exact:

• SD formats at 27.000 MHz: two samples per 13.5 MHz luma sample for the interlaced formats, so 525i59.94 has 1716 samples per line; one per luma sample for the progressive formats, so 480p59.94 has 858.
• HD formats at 74.25 MHz or 74.25/1.001 MHz.
• The three 1080p formats at 50 Hz and above at 148.5 MHz or 148.5/1.001 MHz.

Horizontal columns. H front runs from the end of active picture to the timing reference OH; H back runs from the end of horizontal video sync to the start of active picture.

• SD: OH is the leading edge of the bi-level video sync pulse, and H video sync is that pulse.
• HD: OH is the zero crossing of the tri-level pulse. The negative half of the pair lies at the end of the front porch and is counted there; H video sync is the positive half, from OH to its trailing edge.

For example, a 1080-line row at 60, 59.94, 30, or 29.97 Hz reads 88 | 44 | 148: ST 274's 44 samples from the end of active picture to the pair, 44 negative, 44 positive, and 148 of back porch. A 720p60 or 720p59.94 row reads 110 | 40 | 220, ST 296's 70, 40, 40, and 220. At the other rates only H front widens, to fill the longer line.

Vertical columns. V front and V video sync count whole lines per frame, the two fields of an interlaced format added together. For the interlaced SD formats, the front porch is the pre-equalizing lines and the video sync the broad-pulse lines of each field. A whole-line count cannot express a half line: ST 274 starts field 2's video sync of 1080i at mid-line, so its front porch is 2.5 lines after field 1's picture and 2 after field 2's, 4.5 per frame, where the row's count is 4. Active lines are the count each publication gives for the format.

Rates. A fractional rate is exact: 59.94, 29.97, and 23.98 are the familiar names of 60/1.001, 30/1.001, and 24/1.001 Hz, the rates a 1.001 sample clock gives. The Rate column prints the exact form, vertical_rate in the data file; vertical_rate_hz beside it carries the rounded name.

Interlaced formats in the publication's terms. The analog publications state a line in microseconds, with tolerances EIS does not restate:

• 525i59.94 (SMPTE ST 170): a 63.556 µs line, a 4.7 µs video sync pulse, a 1.5 µs front porch, and about 10.9 µs of blanking;
• 625i50 (ITU-R BT.470): a 64 µs line, a 4.7 µs video sync pulse, a 1.5 µs front porch, and 12 µs of blanking.

A port meets VID-002 inside those tolerances; the row is where a sample-domain design places the active line.

Line. Samples at the sample clock: total per line, active picture, front porch, video sync, back porch.

Frame. Lines per frame: total, active, front porch, video sync; the rate is the field rate of an interlaced format and the frame rate of a progressive one. SD marks the four standard-definition formats.

Picture bandwidth

A format's picture bandwidth is the luma bandwidth its publication specifies for an analog interface. For the two CTA-861 formats, whose publication is digital only, it is half the luma sample rate. The bandwidth of a VIDEO path is compared with it (7.3); the figure is a property of the format, and EIS requires no path to reach it.

Phase

A module that locks to video sync produces its output a fixed time after the video sync. EIS recommends publishing that offset, horizontal and in nanoseconds, at each listed format, and any adjustment the module offers, so that several generators locked to one video sync can be lined up on the screen.

Verification

A maker compares samples per line, lines per frame, field or frame rate, and video sync pulse width and placement with the tables and the cited publication. tests/video_timings_contract.py checks every row that has an entry in its test fixture, a timing contract measured on hardware, clock for clock; the three 148.5 MHz rows, 1080p50, 1080p59.94, and 1080p60, are listed from their publication and are not in the contract.