Decklink Capture

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Decklink Capture

Reuben Martin

I’ve built 2.6.0 with decklink support, but I haven’t been able to work out
how to interface with it. (Even after poking around in the code)

Is there info / documentation on this somewhere? Specifically I can’t figure out
how to set the audio / video input types and modes.

-Reuben
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Re: Decklink Capture

Carl Eugen Hoyos
Reuben Martin <reuben.m <at> gmail.com> writes:

> I’ve built 2.6.0 with decklink support

Please understand that only current FFmpeg git
head is supported on this mailing list.

> but I haven’t been able to work out  how to
> interface with it. (Even after poking around in
> the code)
>
> Is there info / documentation on this somewhere?

http://ffmpeg.org/ffmpeg-devices.html#decklink-1
Is this page particularly difficult to find?

Carl Eugen
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Re: Decklink Capture

Reuben Martin
On Wednesday, March 11, 2015 07:14:31 AM Carl Eugen Hoyos wrote:
> http://ffmpeg.org/ffmpeg-devices.html#decklink-1
> Is this page particularly difficult to find?

That is for output. There is nothing there in regard to selecting it as an
input. How do I select the input interface? My card has 5 different video input
interfaces, and 3 audio input interfaces. Is both audio and video implied when
setting the device as an input, or do you need to specify input devices for
audio and video separately?

I’ve used bmdtools and piped it to ffmpeg for quite a while, and they work fine.
I’m just curious about trying to access it directly.

-Reuben
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Re: Decklink Capture

Reuben Martin
In reply to this post by Carl Eugen Hoyos
On Wednesday, March 11, 2015 07:14:31 AM Carl Eugen Hoyos wrote:
> http://ffmpeg.org/ffmpeg-devices.html#decklink-1
> Is this page particularly difficult to find?

And now that I go back and check, I see that there is a section for decklink
input that either I totally missed, or didn’t exist when I was last looking at
it.

-Reuben
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Re: Decklink Capture

Dave Rice-3
In reply to this post by Reuben Martin

> On Mar 11, 2015, at 7:01 PM, Reuben Martin <[hidden email]> wrote:
>
> On Wednesday, March 11, 2015 07:14:31 AM Carl Eugen Hoyos wrote:
>> http://ffmpeg.org/ffmpeg-devices.html#decklink-1
>> Is this page particularly difficult to find?
>
> That is for output. There is nothing there in regard to selecting it as an
> input. How do I select the input interface? My card has 5 different video input
> interfaces, and 3 audio input interfaces.

You can select the input device. Use the -list_devices option to see what is available. However within a single device that has multiple inputs can you not select the input of that device in the same way that bmdcapture can. To set the input, use the Blackmagic Control panel to select the audio and video input.

> Is both audio and video implied when
> setting the device as an input, or do you need to specify input devices for
> audio and video separately?

Yes both video and audio is implied in one decklink input.

> I’ve used bmdtools and piped it to ffmpeg for quite a while, and they work fine.
> I’m just curious about trying to access it directly.

Same here, though I still use bmdtools. I'm curious how you compare the two.
Dave Rice
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Re: Decklink Capture

Reuben Martin
On Wednesday, March 11, 2015 07:19:14 PM Dave Rice wrote:
> You can select the input device. Use the -list_devices option to see what is
> available. However within a single device that has multiple inputs can you
> not select the input of that device in the same way that bmdcapture can. To
> set the input, use the Blackmagic Control panel to select the audio and
> video input.

Thanks, that makes more sense. I’m used to bmdtools style of over-riding
whatever is set in the control panel for the input interfaces.

One other question that comes to mind: What happens when there are multiple
devices of the same model? The documentation seems to indicate using the
device name instead of device index.

> > I’ve used bmdtools and piped it to ffmpeg for quite a while, and they work
> > fine. I’m just curious about trying to access it directly.
>
> Same here, though I still use bmdtools. I'm curious how you compare the two.

I’m hoping less overhead due to the elimination of all the memory copy going
on with the pipe. I won’t be able to test till tomorrow.

-Reuben
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Re: Decklink Capture

Reuben Martin
On Wednesday, March 11, 2015 06:43:11 PM you wrote:

> On Wednesday, March 11, 2015 07:19:14 PM Dave Rice wrote:
> > > I’ve used bmdtools and piped it to ffmpeg for quite a while, and they
> > > work
> > > fine. I’m just curious about trying to access it directly.
> >
> > Same here, though I still use bmdtools. I'm curious how you compare the
> > two.
> I’m hoping less overhead due to the elimination of all the memory copy going
> on with the pipe. I won’t be able to test till tomorrow.
>

It did minor testing today and didn’t notice anything abnormal aside from
ffplay complaining quite verbosely about buffer overruns when opening directly
with ffplay. Otherwise, there is a small reduction in overhead, and the video
is smoother when reducing the output framerate to half that of the input. (60
to 30 in my case)

-Reuben

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Re: Decklink Capture

Dave Rice-3

> On Mar 12, 2015, at 7:30 PM, Reuben Martin <[hidden email]> wrote:
>
> On Wednesday, March 11, 2015 06:43:11 PM you wrote:
>> On Wednesday, March 11, 2015 07:19:14 PM Dave Rice wrote:
>>>> I’ve used bmdtools and piped it to ffmpeg for quite a while, and they
>>>> work
>>>> fine. I’m just curious about trying to access it directly.
>>>
>>> Same here, though I still use bmdtools. I'm curious how you compare the
>>> two.
>> I’m hoping less overhead due to the elimination of all the memory copy going
>> on with the pipe. I won’t be able to test till tomorrow.
>>
>
> It did minor testing today and didn’t notice anything abnormal aside from
> ffplay complaining quite verbosely about buffer overruns when opening directly
> with ffplay.

Try -re before the input.

> Otherwise, there is a small reduction in overhead, and the video
> is smoother when reducing the output framerate to half that of the input. (60
> to 30 in my case)

What OS are you using?
Dave Rice
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Re: Decklink Capture

Reuben Martin
On Thursday, March 12, 2015 08:01:04 PM Dave Rice wrote:

> > On Mar 12, 2015, at 7:30 PM, Reuben Martin <[hidden email]> wrote:
> >
> > On Wednesday, March 11, 2015 06:43:11 PM you wrote:
> >> On Wednesday, March 11, 2015 07:19:14 PM Dave Rice wrote:
> >>>> I’ve used bmdtools and piped it to ffmpeg for quite a while, and they
> >>>> work
> >>>> fine. I’m just curious about trying to access it directly.
> >>>
> >>> Same here, though I still use bmdtools. I'm curious how you compare the
> >>> two.
> >>
> >> I’m hoping less overhead due to the elimination of all the memory copy
> >> going on with the pipe. I won’t be able to test till tomorrow.
> >
> > It did minor testing today and didn’t notice anything abnormal aside from
> > ffplay complaining quite verbosely about buffer overruns when opening
> > directly with ffplay.
>
> Try -re before the input.

-re doesn’t apply to ffplay.
 
> > Otherwise, there is a small reduction in overhead, and the video
> > is smoother when reducing the output framerate to half that of the input.
> > (60 to 30 in my case)

And by smoother, I just mean that discarding every other frame seems to flow
smoother on the playback. I think there may be something different going on
with how the timestamps on frames work when pulling directly from source as
opposed to a pipe. But then again the perceived difference is subtle, so it may
just be placebo effect.

>
> What OS are you using?

Gentoo
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Re: Decklink Capture

Carl Eugen Hoyos
In reply to this post by Reuben Martin
Reuben Martin <reuben.m <at> gmail.com> writes:

> On Wednesday, March 11, 2015 07:14:31 AM Carl Eugen Hoyos wrote:
> > http://ffmpeg.org/ffmpeg-devices.html#decklink-1
> > Is this page particularly difficult to find?
>
> And now that I go back and check, I see that there
> is a section for decklink input that either I
> totally missed

I fixed the order, thank you for the report!

Carl Eugen

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Re: Decklink Capture

looxonline
In reply to this post by Reuben Martin
Reuben Martin wrote
One other question that comes to mind: What happens when there are multiple
devices of the same model? The documentation seems to indicate using the
device name instead of device index.
So I have just compiled FFMPEG with decklink support on OSX (quite a mission in itself) only to face this issue. I have two Decklink SDI 4K cards running in one machine and because they are referenced using literal text and not numeric identifiers (as with BMDcap) I can only seem to get one to work with FFMPEG at a time.

I'm very new to FFMPEG and OSX so digging into the code and trying to find alternate ways to reference the cards or even ways to adjust the current references is beyond me at the moment. I was wondering if anyone has had a similar experience and managed to overcome it or if anyone knows how I could reference the cards using some other method.

Thanks.