[MPlayer-users] MPlayer pnm frame extraction and psnr-video.sh

[David Thompson]

Hello:

If anyone is interested, I think I have found a way to compare the VC-1
WMV and H.264 MOV files that seems to work.

If I run the mplayer command (on both source and compared file frame
extraction) with the flag -vf crop=1920:1080, so:
mplayer -vf crop=1920:1080 -frames $LastFrame -nosound -vo pnm ...

This allows for a comparison between the original source (Uncompressed
MOV) and the compressed VC-1 WMV file.

To check the validity of this on the two MOV files (with frames in
uncompressed video and H.264 compressed video extracted at 1084 rows), I
ran both the original script without any MPlayer options and the
modified script adding the option -vf crop=1920:1080 and got the exact
same PSNR value:

Normal - PSNR:;26.11892455331689637643 dB
Resize/Cropped - PSNR:;26.11892455331689637643 dB

Therefore, since these values are the same, I am accepting as a basis
for some further testing that this is a valid means of comparing the
vc-1 and the h.264 mov (each via PSNR in relation to source).

Please feel free to let me know if any of my logic here is incorrect!

Cheers,

David


On Tue, 2008-08-05 at 17:23 +0100, David Thompson wrote:
> Hello:
> 
> I have a question regarding MPlayer and frame extraction - particularly
> for use in performing a psnr comparison via pnmpsnr - as in the
> psnr-video.sh script included in tools in the MPlayer project.
> 
> I have two types of videos I am hoping to compare to each other via a
> psnr comparison of each to the uncompressed source: These are H.264 MOV
> and VC-1 WMV files encoded at 1920x1080 from a 1920x1080 source.
> 
> The problem is that the PNM frames extracted by MPlayer from both the
> source and the Quicktime H.264 files are 1920x1084 in size, so although
> these compare fine, the frames extracted from the WMV VC-1 file are
> exactly 1920x1080.  Therefore, since they have a different number of
> rows, they can't be compared via pnmpsnr.
> 
> Can anyone explain to me why the pnm frames extracted from the
> uncompressed and quicktime videos are 1920x1084 in size, when the
> uncompressed source in indeed 1920x1080 and the quicktime videos were
> transcoded at 1920x1080 frame resolution?
> 
> Also, I would greatly appreciate any advice on how to possibly get
> around this issue!
> 
> Cheers,
> 
> David
> 
> 
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