[theora] Loseless Video Codec

[Basil Mohamed Gohar]

On 01/08/2010 08:00 AM, Maik Merten wrote:
>
> Perhaps mplayer (or any other tool writing YUV video data) and dump_psnr 
> (example program of libtheora, 
> http://svn.xiph.org/trunk/theora/examples/dump_psnr.c) would work:
>
> "mplayer -vo yuv4mpeg my-video-file" will dump the decoded stream to 
> stream.yuv.
>
> If "dump_psnr original.yuv ljpeg.yuv" gives an infinite score your most 
> likely rather lossless ;-)
>
>
> Maik
>   
The chroma subsampling that mplayer uses/converts to when using yuv4mpeg
output is always 4:2:0.  This is not useful if you started-off with a
different subsampling, such as 4:4:4 or 4:2:2, as chroma sampling
conversions are not lossless in and of themselves, even going
back-and-forth (higher-lower-higher).

The way I've done it is to dump the raw, decompressed video to a file,
compare filesizes, and if they are the same, then I hash them and
compare the hashes.  Then I know they are truly identical.

For example, this works when I have a Y4M video with yuv420p pixel
format, and I then I compress it using the FFV1 lossless video codec. 
If I decompress the FFV1-compressed video back into Y4M format, the
resulting file is bit-for-bit identical to the original Y4M file, as it
should be.

The same process SHOULD work for all other lossless video codec,
provided they support the pixel formats you're using.