[FFmpeg-devel] [PATCH] decklink: support all valid numbers of audio channels

Matthias Hunstock atze at fem.tu-ilmenau.de
Sun Dec 20 15:28:41 CET 2015

Am 20.12.2015 um 15:11 schrieb Nicolas George:
> Le decadi 30 frimaire, an CCXXIV, Matthias Hunstock a écrit :
>> Decklink cards actually do just some bitbanging: take digital input in
>> "raw" format (AFAIK UYVY422 10 bit, PCM 16bit) and copy that into your RAM.
> Take digital input... from where?

Ok, the bigger picture:

The BlackMagic DeckLink series are capture (and sometimes playout)
cards, mostly having SDI in-/outputs, sometimes also HDMI; some older
models have analog inputs (RGB component, YUV component and so on) and
do ADC themselves.

So the digital input is in most cases (HD-)SDI or HDMI, which also
includes audio. Since there are well-known "pix_fmts" on the wire, there
is only little conversion available in the cards. AFAIK only 10bit/8bit
conversion on the video data.

So using these cards means you get blasted with raw UYVY422 data and
either 2, 8 or 16 PCM 16bit audio channels. Reverse logic applies for

>> Another possibility is to demux each channel as a mono track. Would this
>> make more sense?
> It depends on the use case, and therefore on where the channels come from.

Yes. IMHO a channel mapping is needed in 95% of the use cases, so if it
is valid to have an unspecified channel layout than it should be used.


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