[FFmpeg-devel] [PATCH] avdevice/decklink_dec: Extract NTSC VANC

Marton Balint cus at passwd.hu
Mon Feb 5 21:04:00 EET 2018

On Mon, 5 Feb 2018, Devin Heitmueller wrote:

> Hello Marton,
>> I thought you are working on an updated patch, or I just missed the new 
>> one? The email you replied to here definitely contains the old, without 
>> interleaved VANC autodetection or proper width for get_metadata.
> I did some digging into this after discussion with Ray (both by 
> reviewing the SMPTE specs as well as doing some testing here with my 
> Sencore MRD4400 decoder).  The use of VANC over both luma and chroma is 
> because it’s an SD format. Hence it will only be present in specific 
> modes.  When doing HD formats, the VANC packets will be exclusively 
> found in the luma region.

Have you found which standard contains reference to interleaved VANC?

> That said, the list of modes should probably be expanded to include all 
> the SD resolutions (although you’re unlikely to see CEA-708 over 
> non-NTSC streams).  However I don’t think it would be a good idea to 
> attempt to ‘autodetect” by applying both algorithms over all VANC lines 
> regardless of mode.

I think the plan was to check if the mode is NTSC _and_ the first VANC 
header is present in an interleaved way. So the HD modes would remain as 

I only found ITU-R BT.1364-3 which states that luma and chroma are 
separate VANC spaces, so that is why I thought autodetection for even 
NTSC would make it more compatible with newer equipment respecting this 

If you think this is unnecesary then so be it, I have no experience with 
real life baseband NTSC signals.


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