From: "Daniel W. S. Almeida" <dwlsalmeida@gmail.com>
To: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: "r.verdejo@samsung.com" <r.verdejo@samsung.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"nicolas@ndufresne.ca" <nicolas@ndufresne.ca>,
"linux-kernel-mentees@lists.linuxfoundation.org"
<linux-kernel-mentees@lists.linuxfoundation.org>,
"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>
Subject: Re: [Linux-kernel-mentees] [v10 0/4] media: vidtv: Implement a virtual DVB driver
Date: Fri, 11 Sep 2020 09:18:20 -0300 [thread overview]
Message-ID: <25F257A6-C651-4BE7-8482-14FCF121D88F@getmailspring.com> (raw)
In-Reply-To: <20200911100200.25214c37@coco.lan>
Hey Mauro,
> Thanks for all the hard work on it. Very much appreciated!
>
> I finally found some time to test it. For now, just a quick
> test from my side, without passing any arguments to the
> driver.
>
That's nice!
> My plan is to write some patches on the top of yours, in order to
> address the problems I'll find on it. If not something more critical
> won't be solved in time, we may still add it at staging/media.
> Let's see.
OK
> 3. dvbv5-zap wrote an empty audio file (without -P flag).
> Probably there are still some issues at the program
> channel descriptor or service;
I don't remember whether I tried this. I tried dumping the stream to a
file with dvbzap, which should work. By the way, I guess we should be
comparing the output to this
$ ffmpeg -f lavfi -i sine=frequency=1000:duration=5 -ac 2 -c:a s302m
-strict -2 out.ts
Since it produces a playable transport stream file that actually sounds
like a sine tone.
Inspecting ffmpeg & vidtv output side by side in dvbinspector, you'll
see that they're mostly the same. I have a separate PID for the PCR and
some other minor differences.
> 4. The provider service field is null. Perhaps we could
> add some string there, like "linuxtv.org".
> 5. Maybe we could also add a simple NIT table, just to
> avoid dvbv5-scan to wait for it until timeout.
>
> Also, it probably makes sense to add a debugfs interface in
> order to allow injecting errors at the stream at runtime.
Sure. This is fun, sign me up for it.
As I said in a previous email, I think the buffer in vidtv_s302m.c is
not exactly what we want. It sounds like noise.
I got it from here:
https://www.daycounter.com/Calculators/Sine-Generator-Calculator.phtml
I will just copy what I had in a previous email here:
>How do I compute the values for a sine wave such that it can be played indefinitely?
>
>I was thinking about this: (just spitballing here..)
>
>sampling_rate_khz = 48000
>buffer_size = sampling_rate_khz * seconds
>i = 0
>
>for i < buffer_size:
>buffer[i] = 32767 * sin( 2 * PI * freq / (sampling_rate_khz * i) )
>
>
>but rather I want to precompute a single period for a given frequency
>such that I can loop on the array indefinitely
By the way, after some time trying out stuff, I guess this is actually
what we need in vidtv_s302m_write_frame:
static u32 vidtv_s302m_write_frame(struct vidtv_encoder *e,
u16 sample)
{
u32 nbytes = 0;
struct vidtv_s302m_frame_16 f = {};
struct vidtv_s302m_ctx *ctx = e->ctx;
/* from ffmpeg: see s302enc.c */
u8 vucf = ctx->frame_index == 0 ? 1 : 0;
f.data[0] = reverse[sample & 0xff];
f.data[1] = reverse[(sample & 0xff00) >> 8];
f.data[2] = (vucf << 4) | (reverse[(sample & 0x0f)] >> 4);
f.data[3] = reverse[(sample & 0x0ff0) >> 4];
f.data[4] = reverse[(sample & 0xf000) >> 12] >> 4;
nbytes += vidtv_memcpy(e->encoder_buf,
e->encoder_buf_offset,
VIDTV_S302M_BUF_SZ,
&f,
sizeof(f));
e->encoder_buf_offset += nbytes;
ctx->frame_index++;
if (ctx->frame_index >= S302M_BLOCK_SZ)
ctx->frame_index = 0;
return nbytes;
}
i.e. see: https://docplayer.net/37828038-For-television-mapping-of-aes3-data-into-an-mpeg-2-transport-stream.html
Figure 5, page 4.
Lastly, I am somewhat new to C, so a few things might look odd here and
there. If you come across something that's too verbose tell me and I
will try to tidy it up.
--thanks
-- Daniel
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next prev parent reply other threads:[~2020-09-11 12:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-21 12:58 [Linux-kernel-mentees] [v10 0/4] media: vidtv: Implement a virtual DVB driver Daniel W. S. Almeida
2020-08-21 12:58 ` [Linux-kernel-mentees] [v10 1/4] media: vidtv: implement a tuner driver Daniel W. S. Almeida
2020-08-21 12:58 ` [Linux-kernel-mentees] [v10 2/4] media: vidtv: implement a demodulator driver Daniel W. S. Almeida
2020-08-21 12:58 ` [Linux-kernel-mentees] [v10 3/4] media: vidtv: add a bridge driver Daniel W. S. Almeida
2020-09-15 11:53 ` Geert Uytterhoeven
2020-09-15 13:26 ` Daniel W. S. Almeida
2020-09-15 13:35 ` Geert Uytterhoeven
2020-09-15 18:13 ` Daniel W. S. Almeida
2020-09-16 7:01 ` Mauro Carvalho Chehab
2020-08-21 12:58 ` [Linux-kernel-mentees] [v10 4/4] media: Documentation: vidtv: Add ReST documentation for vidtv Daniel W. S. Almeida
2020-09-11 8:02 ` [Linux-kernel-mentees] [v10 0/4] media: vidtv: Implement a virtual DVB driver Mauro Carvalho Chehab
2020-09-11 12:18 ` Daniel W. S. Almeida [this message]
2020-09-11 13:10 ` Mauro Carvalho Chehab
2020-09-11 13:56 ` Mauro Carvalho Chehab
2020-09-12 2:54 ` Daniel W. S. Almeida
2020-09-12 7:38 ` Mauro Carvalho Chehab
2020-09-12 8:21 ` Hans Verkuil
2020-09-12 9:15 ` Mauro Carvalho Chehab
2020-09-12 14:49 ` Daniel W. S. Almeida
2020-09-12 17:57 ` Mauro Carvalho Chehab
2020-09-14 8:33 ` Hans Verkuil
2020-09-12 8:35 ` Hans Verkuil
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