[FFmpeg-devel] [PATCH] avfilter: add framerate video filter

[Robert Krüger]

On Sun, Aug 30, 2015 at 1:45 PM, Andy Furniss <adf.lists at gmail.com> wrote:

> Carl Eugen Hoyos wrote:
>
>> Robert Krüger <krueger <at> lesspain.de> writes:
>>
>> The only other thing I noticed was that the stream seams to be
>>> marked as interlaced when it comes out of the first il filter,
>>> which causes warnings like these:
>>>
>>> [Parsed_framerate_1  <at>  0x7fa4e3426080] Interlaced frame found -
>>> the output will not be correct.
>>>
>>
>> This sounds like an issue to me but we probably need an option for il
>> to disable changing the interlaced flag if another usecase for the
>> filter was found.
>>
>
> Isn't fields being marked as interlaced correct though?
>
> I mean it's not progressive video that is produced, as each field is
> offset by one line and anything that could process correctly, still
> needs to know whether a field is top or bottom.
>
> I don't know whether the framerate filter can handle fields or not, if
> it can, there should be code that takes account of top/bottom. If there
> isn't that code then I guess it really does need de-interlaced
> progressive full height frames as input.
>
>
I guess the point is that the signal can be viewed as progressive after the
il filter in deinterleave mode as it has the fields stacked on top of each
other in each half of the picture. I thought that's the whole point of il,
to apply filters that were not written with interlacing in mind and by this
trick (deinterleave, process each field like a progressive picture,
reinterleave) get some things done that would not be possible otherwise. Of
course that's not really true with respect to picture timing but all
progressive spatial filters should work using this approach (not taking
into account potential quality side effects that the broadcast guys know
best). I think the il filter signaling a progressive picture after
deinterleaving would be more correct than signaling interlaced but if there
is no consensus, it could let the user decide this using an option.