Quote:
Originally Posted by Alleycat
I rebuilt a concert blu-ray which had 720 x 480i mpeg 2 source with a 16:9 display aspect ratio. I noticed that the rebuilt version has small black bars at the top and bottom and the picture was of reduced height (slightly squashed) compared to the original. When I used the hidden option show_encoder=1, x264 reported the following: "lav [info]: 720x480i 32:27 @ 30000/101 fps (cfr)"
I could see that bd-rb was then telling x264 to use SAR=40/33 when doing the re-code, which I believe is the cause of this problem. Is there a way of forcing bd-rb to preserve the original SAR value?
|
Is your source a DVD? 32:27 = 1.1852 is the 'Generic' PAR of anamorph 16:9 NTSC DVDs. It is an assumption because the true PAR of DVDs/mpeg2 cannot be read from the video stream. The DVD could also have been authored using the ITU PAR of 1.212954 for 16:9. We simply don't know.
BD-RB uses the mpeg4 SAR of 40:33 = 1.212121... for x264 16:9 anamorph 720x480 encoding. It is AVC/mpeg4/blu-ray compliant and a very close approximation to the ITU PAR of 1.212945, but exhibits the well known aspect ratio difference of 2.3% compared to the 'Generic' PAR of 1.1852. This slight difference is normally not even noticed. As far as I remember you can't change the SAR in BD-RB to avoid non-compliant mpeg4/AVC video.
Thinking about it and hoping I remembered all this correctly, I am now wondering why BD-RB added top and bottom borders rather than left and right 8 pixels each. Did your original already come with any borders? Did you resize? What is your playback scenario? Does your player/TV add the top/bottom borders rather than BD-RB? Does your player read the SAR or force 16:9 DAR playback?