Partial attempt at fixing interlacing support.

First try using no interlacing and fallback to driver's default if it
isn't possible. Might fix some issues. We still need to declare images
as interlaced to VLC afterwards, but that's another problem.

modules/access/v4l2.c

@@ -1917,7 +1917,20 @@ static int OpenVideoDev( vlc_object_t *p_obj, demux_sys_t *p_sys, bool b_demux )
                 }
             }
             /* Try and set user chroma */
-            if( !IsPixelFormatSupported( p_demux, fmt.fmt.pix.pixelformat ) || ( fmt.fmt.pix.pixelformat && v4l2_ioctl( i_fd, VIDIOC_S_FMT, &fmt ) < 0 ) )
+            bool b_error = !IsPixelFormatSupported( p_demux, fmt.fmt.pix.pixelformat );
+            if( !b_error && fmt.fmt.pix.pixelformat )
+            {
+                if( v4l2_ioctl( i_fd, VIDIOC_S_FMT, &fmt ) < 0 )
+                {
+                    fmt.fmt.pix.field = V4L2_FIELD_ANY;
+                    if( v4l2_ioctl( i_fd, VIDIOC_S_FMT, &fmt ) < 0 )
+                    {
+                        fmt.fmt.pix.field = V4L2_FIELD_NONE;
+                        b_error = true;
+                    }
+                }
+            }
+            if( b_error )
             {
                 msg_Warn( p_demux, "Driver is unable to use specified chroma %s. Trying defaults.", p_sys->psz_requested_chroma );
                 fmt.fmt.pix.pixelformat = 0;
@@ -1932,9 +1945,15 @@ static int OpenVideoDev( vlc_object_t *p_obj, demux_sys_t *p_sys, bool b_demux )
             for( i = 0; i < ARRAY_SIZE( p_chroma_fallbacks ); i++ )
             {
                 fmt.fmt.pix.pixelformat = p_chroma_fallbacks[i];
-                if( IsPixelFormatSupported( p_demux, fmt.fmt.pix.pixelformat )
-                 && v4l2_ioctl( i_fd, VIDIOC_S_FMT, &fmt ) >= 0 )
+                if( IsPixelFormatSupported( p_demux, fmt.fmt.pix.pixelformat ) )
+                {
+                    if( v4l2_ioctl( i_fd, VIDIOC_S_FMT, &fmt ) >= 0 )
+                        break;
+                    fmt.fmt.pix.field = V4L2_FIELD_ANY;
+                    if( v4l2_ioctl( i_fd, VIDIOC_S_FMT, &fmt ) < 0 )
                         break;
+                    fmt.fmt.pix.field = V4L2_FIELD_NONE;
+                }
             }
             if( i == ARRAY_SIZE( p_chroma_fallbacks ) )
             {