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. -- 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
