How to determine if 720p really is what is states 'on the tin'

[DB83]

Now if this belongs elsewhere then do educate me so I can arrange to have it moved.

Over at another forum, I was reading posts that a stream was not really 720p but, essentially, upscaled from one of the other resolutions (with a corresponding increase in bitrate) that the service provides namely 360p or 480p.


So, rather than the obvious, i.e. attempting to count the pixels, is there another way to determine if what you think you are getting is what you actually receive. After all, even YT provides the same vid at different resolutions/bitrate.

[Sharc]

Principle:
Downscale the video, then upscale it back and compare this with the original (best by interleaving). If you see no difference when stepping through the interleaved frames then the true resolution is the downscaled version.

Try something like this in Avisynth (for progressive source):

LWLibavVideoSource("your source")
a=last
dx=854 #downscaled horizontal dimension
dy=480  #downscaled vertical dimension
taps=31
lanczosresize(dx*2, dy*2, 0.5, 0.5, taps=taps)
pointresize(dx, dy)
spline36resize(a.Width,a.Height)

interleave(a.Subtitle("Original"),last.Subtitle("Downscaled"))

Edit: You can use a simpler downscaling method but then you include the effect of the lowpass filter. You may find a compromise:

LWLibavVideoSource("your source")
a = last
dx=720 #downscaled horizontal dimension
dy=576   #downscaled vertical dimension
res = a.Lanczos4Resize(dx,dy).sharpen(0.12).Lanczos4Resize(a.Width,a.Height)
Interleave(a.Subtitle("Original"),res.Subtitle("Downscaled"))