[x264-devel] Lossless with 10bit pixel depth

[Simon Dumke]

Hi all,

I was today experimenting with lossless encoding in x264 (using ffmpeg).

My experiment was coming in with a raw yuv420 stream, encoding that with 
h264 high444 witch crf=0. Than decoding it again to raw yuv420 and 
making a binary diff to the original.

When using 8bit yuv, this works as expected:

    ffmpeg -f rawvideo -video_size 1024x1280 -pixel_format yuv420 -i
    yuv420-8.yuv -c:v libx264 -pix_fmt yuv420 -profile:v high444 -crf 0
    -preset:v slow h264-8-420.m4v
    ffmpeg -i h264-8-420.m4v -c:v rawvideo -f rawvideo -pix_fmt
    yuv420p10le decompressed-8-420.yuv
    diff -s yuv420-8.yuv decompressed-8-420.yuv

The diff, as expected, resulted in identical files.

Doing the same with a yuv420p10le however, does not:

    ffmpeg -f rawvideo -video_size 1024x1280 -pixel_format yuv420p10le
    -i yuv420-10.yuv -c:v libx264 -pix_fmt yuv420p10 -profile:v high444
    -crf 0 -preset:v slow h264-10-420.m4v
    ffmpeg -i h264-10-420.m4v -c:v rawvideo -f rawvideo -pix_fmt
    yuv420p10le decompressed-10-420.yuv
    diff -s yuv420-10.yuv decompressed-10-420.yuv

Here, while the result looks ok optically, the diff (or a cmp) show a 
lot of differences.

My question: Do i have to do more to have lossless 10bit encoding? Is it 
even possible? Or is there another error in my thinking?

Thanks & regards,

Simon

P.S.: BTW - will support for 12 and 14 bit come at any time in the future?


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