[FFmpeg-devel] [PATCH 2/2] avdevice/decklink_dec: add support for receiving op47 teletext

Aaron Levinson alevinsn at aracnet.com
Mon Jul 3 21:26:02 EEST 2017

On 7/3/2017 1:06 PM, Marton Balint wrote:
> On Mon, 3 Jul 2017, Aaron Levinson wrote:
>>> +22, and lines 318 to 335. Line 6 is the LSB in the mask. Selected lines 
>> which
>>> +do not contain teletext information will be ignored. You can use the 
>> special
>>> + at option{all} constant to select all possible lines, or 
>>> @option{standard} 
>> to
>>> +skip lines 6, 318 and 319, which are not compatible with all receivers.
>>> +
>>> +For SD sources ffmpeg needs to be compiled with 
>>> @code{--enable-libzvbi}. 
>> For HD
>>> +sources on older (pre-4K) DeckLink card models you have to capture 
>>> in 10 
>> bit
>>> +mode.
>> Would be good to indicate that the bit mask is ignored for HD sources.
> Actually it is not. Any HD line can contain an OP47 packet referencing 
> any SD line, the bitmask is checked against the decoded source line 
> number from OP47.
>> The documentation indicates that both SD PAL and HD sources are 
>> supported, but an examination of the changes indicates that only some 
>> HD sources are supported.  Specifically, for HD sources to work, it 
>> expects a width of 1920.  This would cover both 1080i and 1080p, but 
>> it doesn't cover 720p, with is also an HD video mode.  My guess is 
>> that the code has probably only been tested with 1080i as well, and in 
>> that case, it would make sense to only specify 1080i in the 
>> documentation.  Further, since the original code only supports SD PAL, 
>> I would suspect that the latest code has only been tested using "PAL" 
>> frame rates at 1080i, i.e. 1080i50.  If it is unclear if the code will 
>> also work with 1080i59.94 and 1080i60, then it would be best to only 
>> support 1080i50.
> 1080i/p/59.94/60 should work all the same. For 720p different VANC lines 
> might be needed. I will change the HD references to "Full HD" so it will 
> be more clear.

Searching for "full HD" tends to indicate that term is usually 
associated with 1080p but not with 720p nor 1080i (for example, at 
http://www.pcmag.com/article2/0,2817,2413044,00.asp ).  I think it would 
be clearer to call out the specific video modes that are supported.

Aaron Levinson

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