Reply To: OG Xbox Optimal Timings (PAL/NTSC)
That’s an interesting question. My timings that are at junkerhq are based on the Xcalibur video encoder and apply to the Xbox 360 ANA/HANA as well for 640×480. I also misremembered which revision was first to have the Xcalibur, so I didn’t realize at first we’re talking about the Focus Enhancements video encoder.
When I went through the datasheets for the Conexant CX25871 and Focus Enhancements FS454 encoders from the earlier revisions of the Xbox, I noticed that their default timings are a bit strange and may not use the same 12.273 MHz square pixel mode. Both have scalers built-in and are designed to take a PC resolution and convert it to 480i/p or 576i/p, with passthrough available for progressive and HDTV modes.
It’s possible that they neither of them, or at least the Focus Enhancements encoder, output square pixel mode natively when set up by the Xbox, but convert everything to BT.656 timings for 480i and 576i. This is suggested by your timings – if the 640 pixel raster is scaled up the 720 pixel active area by the encoder, then attempting to sample it as square pixel will require (640÷720)×858 samples total, resulting in 762.67 samples per line.
Interestingly, both the Conexant and Focus Enhancements encoders handle the signal as YCbCr 4:2:2 internally and the Conexant encoder doesn’t output very high quality YPbPr or RGBS at standard definition because the signal passes through the lowpass filters needed for the CVBS signal. The Xcalibur, ANA, and HANA output YPbPr and RGBS with full color bandwidth. At 480p and HDTV resolutions they pretty much route the input as-is to the video DACs.
Each encoder probably needs its own optimal timings. The optimal ones for the Conexant and Focus Enhancement encoders may be different between interlaced and progressive 640×480 rather than just double the clock as in the Xcalibur.
