various: implement sequence pixel aspect ratios and interlacing settings

Implements the following:
- Sequences have pixel aspect ratios that work in tandem with footage PARs
  to render footage correctly. Viewer and export also acknowledge PARs
- Sequences can have interlacing settings. This doesn't do anything yet,
  eventually the renderer will need to interlace/deinterlace/reinterlace
  appropriately in order to conform all the footage to the sequence. Export
  acknowledges interlacing, but this only affects metadata, not the image.

app/codec/oiio/oiiodecoder.cpp

@@ -118,16 +118,14 @@ bool OIIODecoder::Probe(Footage *f, const QAtomicInt *cancelled)
   image_stream->set_width(in->spec().width);
   image_stream->set_height(in->spec().height);
   image_stream->set_format(GetFormatFromOIIOBasetype(in->spec()));
-
-  // FIXME: Haven't looked, does OIIO report pixel aspect ratio somewhere?
-  image_stream->set_pixel_aspect_ratio(1);
+  image_stream->set_pixel_aspect_ratio(GetPixelAspectRatioFromOIIO(in->spec()));
 
   // Images will always have just one stream
   image_stream->set_index(0);
 
   // OIIO automatically premultiplies alpha
-  // FIXME: We usually disassociate the alpha for the color management later, for 8-bit images this likely reduces the
-  //        fidelity?
+  // FIXME: We usually disassociate the alpha for the color management later, for 8-bit images this
+  //        likely reduces the fidelity?
   image_stream->set_premultiplied_alpha(true);
 
   // Get stats for this image and dump them into the Footage file
@@ -181,6 +179,8 @@ FramePtr OIIODecoder::RetrieveVideo(const rational &timecode, const int& divider
   frame->set_video_params(VideoParams(buffer_->spec().width,
                                       buffer_->spec().height,
                                       pix_fmt_,
+                                      GetPixelAspectRatioFromOIIO(buffer_->spec()),
+                                      VideoParams::kInterlaceNone, // FIXME: Does OIIO deinterlace for us?
                                       divider));
   frame->allocate();
 
@@ -294,6 +294,11 @@ PixelFormat::Format OIIODecoder::GetFormatFromOIIOBasetype(const OIIO::ImageSpec
   }
 }
 
+rational OIIODecoder::GetPixelAspectRatioFromOIIO(const OpenImageIO_v2_1::ImageSpec &spec)
+{
+  return rational::fromDouble(spec.extra_attribs.get_float("PixelAspectRatio", 1));
+}
+
 bool OIIODecoder::FileTypeIsSupported(const QString& fn)
 {
   // We prioritize OIIO over FFmpeg to pick up still images more effectively, but some OIIO decoders (notably OpenJPEG)