linux-kernel - Re: [PATCH] media: vidtv: fix build on 32bit architectures

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Date:   Wed, 16 Sep 2020 10:43:42 -0300
From:   "Daniel W. S. Almeida" <dwlsalmeida@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        "r.verdejo@...sung.com" <r.verdejo@...sung.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        "nicolas@...fresne.ca" <nicolas@...fresne.ca>,
        Shuah Khan <skhan@...uxfoundation.org>,
        "linux-kernel-mentees@...ts.linuxfoundation.org" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH] media: vidtv: fix build on 32bit architectures

Hi Mauro, Geert,

> That doesn't seem to be the right thing to do here.
>
> Assuming that sampling rate is 48 kHz, you'll
> have duration = 1.875, which would be rounded to 1.
>
> In other words, the above is identical to:
>
> au->pts = count
>
> Now, I don't know from where that CLOCK_UNIT_90KHZ came from.
>

Mauro, here's my current understanding:

The values for PTS have to be defined in terms of a 90khz clock. 

So for 30fps video, the values for PTS per frame would be:

frame_num/30 * 90000

so 0, 3000, 6000, 9000...etc

The same math is being used here for audio, but instead we have the
total audio sample count and a 48000 samples/sec


I did miss this rounding error though, I'm sorry.