Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> wrote: >Em 05-07-2011 16:02, Andy Walls escreveu: >> Hans Verkuil <hverkuil@xxxxxxxxx> wrote: >>> I can work on the proposal this week for that. The only reason the >fps >>> hasn't been added >>> yet is that I never had the time to do the research on how to >represent >>> the fps reliably >>> for all CEA/VESA formats. Hmm, pixelclock / total_framesize should >>> always work, of course. >>> >>> We can add a flags field as well (for interlaced vs progressive and >>> perhaps others such as >>> normal vs reduced blanking). >>> >>> That leaves the problem with GTF/CVT. I'll get back to that >tomorrow. I >>> have ideas, but >>> I need to discuss it first. >>> >>> Regards, >>> >>> Hans >>> -- >>> To unsubscribe from this list: send the line "unsubscribe >linux-media" >>> in >>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> For fps you could use horizontal_line_freq/lines_per_frame. >> >> However, all of the non-integer fps numbers I have seen in this email >chain all seem to be multiples of 29.97002997 Hz. So maybe you could >just use the closest integer rate with a flag labeled >"ntsc_bw_timing_hack" to indicate the fractional rates. :) > >CEA-861 has some other timings that are not 60 Hz * 1000/1001. Yet, >v4l2_fract >is capable of handling any of such timings, as, whatever frequency >taken, it >needs to be a fractional number. Btw, even some userspace libraries >prefer to >represent fps using a fraction, instead of a float, to avoid rounding >issues. > >> >> That 29.97 Hz number comes from the NTSC decision in 1953(!) to >change the horizontal line freq to 4.5 MHz/286. Note that >> >> (4.5 MHz/286)/525 = 30 * (1000/1001) = 29.97002997 Hz > >One of the rationale for that decision was to avoid flicking issues >with cathodic >ray monitors and fluorescent lamps. > >> It is interesting to see one of the most ingenious analog hacks in TV >history (to achieve color and B&W backward compatabilty while staying >in the 10% tolerance of the old B&W receivers) being codified in >digital standards over 50 years later. It boggles the mind... > >Yes. Bad (and good) API decisions will stay forever. > >Cheers, >Mauro. Oops, yes I see the 60.054 Hz rate corresponds to a 262 line field (524 line frame) at the standard NTSC line rate. Weird stuff. Regards, Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
