[FFmpeg-devel] decklink 24/32 bit question

Douglas Marsh ffmpeg at dx9s.net
Tue Oct 17 22:16:51 EEST 2017

On 2017-10-17 11:59, Moritz Barsnick wrote:

> Did you check out Dave Rice's recent patch (on this list)? It touches
> code in a few more places, and adds an option to select 16 vs. 32 bits.
> Please test, if you can.
> Is your subject indicating that 24 bits depth could also be supported?
> If so, Dave perhaps should expand his patch to cover that.

I did see it!

Been busy, trying to get a video project done and under the belt before 
I start tinkering with dependent things. I *WILL* report back my 
experiences (positive or negative). I was hacking the source before that 
patch and see the two areas that I missed. But his patch added command 
line parameters for selecting (which I prefer). Was going to try it out 
and change the default to 32-bit as well.

I am guessing that some capture hardware may not support higher than 16 
bit depths? If all support higher depths, then why should the default 
not be higher and then let FFMPEG convert the input stream to the 
correct output stream (it might be 16 bits)? Is truncating CPU 
intensive? Dithering be applied? What does the DAC do in hardware when 
outputting 16-bits (truncate or dither)?

Also from what I understand word/sample size is 32-bits but the DAC is 
24 (assuming 8-bits are padded) -- hence why I said 24/32. I only see in 
the SDK 16-bits and 32-bits, but know the documentation for the card I 
have (Studio 4K) states 24-bits. Do others have cards that state 
anything additional over 16 and 32?

--Doug (dx9s)

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