[mythtv] Interlaced vs. Progressive
ijr at case.edu
Sun Feb 26 06:00:30 UTC 2006
On Sunday 26 February 2006 00:14, David Asher wrote:
> I've been following the development of the Internal video player closely
> because I'd love to punt xine for displaying MythVideo stuff -- esp.
> with the advent of DVD menu support.
> But every time I've used it on an .avi (or DVD .iso), the picture
> quality has been terrible. I never bothered to look into why until
> today. It turns out that it appears to be entirely attributable to the
> internal player thinking progressive video is interlaced -- and applying
> the deinterlacer to it. If I disable the deinterlace in TV playback
> options the quality is quite good.
> It appears the "culprit" is detectInterlace which simply says (for non
> 720 video) if the fps is <= 45 it must be interlaced. These videos all
> report ~23.97fps (DVD reports 29.997fps). Of course there is the
> following comment too:
> // The scanning mode should be decoded from the stream, but if it
> // isn't, we have to guess.
> So, obviously, I need to figure out why progressive/interlaced isn't
> being "decoded from the stream".
> I'm happy to look into coding an improved interlace detector -- but
> don't have the slightest idea where to start. Anybody willing to point
> me in the right direction? Other players which do it better learn
> from? I suppose I could resort to adding a key to toggle deinterlace
> from the player... That's pretty icky, though.
Check avformatdecoder.cpp, where it calls SetVideoParams() (two places). Both
are calling it with kScan_Detect, and they _could_ be telling it what the
video style is. In the struct returned by avcodec_decode_video, there are
two fields, 'interlaced_frame' and 'top_field_first' which give that info.
If you got it using that data to pass in to SetVideoParams, it'd probably
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