Aspect ratio help needed

Qyot27 · Post by **Qyot27** » Fri Jun 08, 2007 11:42 am

Qyot27 wrote:However, if you are dealing with an MPEG-1 or MPEG-2 file, then there isn't any reencoding necessary to correct the issue. Demux the streams with TMPGEnc, get ahold of a program called ReStream, and run the .m1v (or .m2v, whichever you have) through it, specifying it to have a 16:9 flag. Then remux the fixed video stream with the audio stream and voila. I always use ReStream to make things anamorphic since I don't trust TMPGEnc to do it correctly - not to mention it's easier to figure out; I could never get TMPGEnc's settings right during the encode.

I knew I should have checked better. ReStream only officially supports MPEG-2. I think there is a similar program for MPEG-1, though.

post-it · Post by **post-it** » Fri Jun 08, 2007 5:09 pm

Qyot27 wrote:On the DVDs, Elfen Lied is stored as 720x480 with an anamorphic flag ... 16:9 but it would be the proper resolution for encoding hard letterboxing for DVD since the image itself and both of the borders would be multiples of 16) ...

umm, just out of curiousity ( and please correct me if/when I'm wrong here ) I thought Mpeg's were sized by 8's ... not 16's --- I believe ErMaC said something about that years ago ....

Scintilla · Post by **Scintilla** » Fri Jun 08, 2007 5:24 pm

post-it wrote:
Qyot27 wrote:On the DVDs, Elfen Lied is stored as 720x480 with an anamorphic flag ... 16:9 but it would be the proper resolution for encoding hard letterboxing for DVD since the image itself and both of the borders would be multiples of 16) ...
umm, just out of curiousity ( and please correct me if/when I'm wrong here ) I thought Mpeg's were sized by 8's ... not 16's --- I believe ErMaC said something about that years ago ....

Each macroblock is 8 pixels by 8 pixels, but you're forgetting that one pixel in the chroma channels is equivalent to 4 pixels in the luma channel. So, an 8x8 macroblock in U or V = 16x16 macroblock in Y.

That's why it's much better for compression if letterboxing is a multiple of 16 pixels tall.

post-it · Post by **post-it** » Fri Jun 08, 2007 10:42 pm

Zero1 · Post by **Zero1** » Sat Jun 09, 2007 7:39 am

Macroblocks in standards MPEG-4 Visual and older tend to use 16x16 pixel macroblocks. It's the DCT which works with 8x8.

Newer standards like H.264 use 4x4, 8x8, 16x16 and combinations of those, yet it is still good practice to use mod 16 because it still has 16x16 pixel macroblocks.