[FFmpeg-devel] [PATCH] Change default behaviour of scale filter from 'progressive' to 'auto'

Tim Nicholson nichot20 at yahoo.com
Mon Apr 2 09:43:51 CEST 2012

On 31/03/12 01:40, Carl Eugen Hoyos wrote:
> Reimar Döffinger <Reimar.Doeffinger <at> gmx.de> writes:
>> Which of course is generally related to any kind of 
>> "interlaced content" flag being really, really unreliable.

I thought it was now much better.....

> Which is why I am slightly against this patch:
> Afaict, on DVB-T (SD), all material is signalled as being 
> interlaced, although all movies and series are progressive 
> (because 24Hz stretched and "interlaced" to 50Hz does not 
> produce visible fields).

Ahh, the so called PSF mode, (Progressive Sequential Field). The trouble
is there is may also be true interlaced material within these streams as
well. In fact within a single program you may find a mix of both types
if the content switches between studio and film based material. So I
would challenge the "all material" in your statement.

> I suspect who works with interlaced material knows it 
> and can set the scaling correctly.

Whilst this is true there is one major snafu in the current arrangement,
and that is that quite often in a filterchain a scale filter gets auto
inserted between other filters, and by default handles material
progressively. Therefore when building filtergraphs one has to be very
careful to forced add scale filters with interlace enabled at every
place where a scale filter would otherwise be auto inserted.

It is much neater, and leads to clearer filtergraphs, if one could force
the interlace type at the start of a filterchain using 'setfield' and
leave the rest of the chain containing just the required filters for the
actual required function.

Handling PSF material as interlaced can mean that non optimal
interpolation is used, but the material is not otherwise damaged.
However the reverse of handling interlaced as progressive can render
material unusable..


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