vertical resolution of bob output

[peter71]

Hi,

I compress my DV footages in 50 fps progressive H.264, using the bob filter on the end of the avisynth script. The bob filter keeps the original resolution of the footage, however I guess every second scanline of the output video is identical with the one above it (may I be wrong ?). My question: can I decrease the vertical resolution of the frame server output (that is fed in ffmpeg) without losing any visual information ? I'd compress with a SAR (sample aspect ratio) that would result in a 4:3 screen, so the decoder should scale up the image vertically.

Thanks in advance,
Peter

[wonkey_monkey]

bob (more or less) just blends the scanlines above and below to create the new ones, so it's a bit of a waste of bits.

You could do a separatefields instead of a bob, which would reduce the vertical resolution by a factor of 2, double the framerate, and essentially keep all of the information, but then it will suffer in compression, and you'd have to do more work to reconstruct the original scanlines afterwards - the scanlines in alternate frames will be from different spatial positions, which I doubt the codec will be able to handle correctly.

The best options are either just to encode interlaced h264, or to use a better bobber (yadif is good and pretty fast).

David

[peter71]

Thanks for the explanation. Now that I considered the problem again I think I will stick to the good old bob, and will try out yadif. I don't like storing my videos interlaced, as I never watch them on TV.

[Didée]

Don't decide before you've seen them all.

Consider Stockholm (http://forum.doom9.org/showthread.php?p=1150279#post1150279), as an example for what an "exhaustive" bob filter can do, compared to the "more simple" collegues.

[wonkey_monkey]

Thanks for the explanation. Now that I considered the problem again I think I will stick to the good old bob, and will try out yadif. I don't like storing my videos interlaced, as I never watch them on TV.

My suggestion that you leave them interlaced wasn't under the assumption you'd be watching them on TV - if you're only going to use "plain old bob" anyway, you may as well as encode interlaced and use a player that bobs on playback, such as VLC - and VLC can also Yadif on playback (apparently).

That way you don't waste bits on those bobbed scanlines.

David

[R3Z]

My suggestion that you leave them interlaced wasn't under the assumption you'd be watching them on TV - if you're only going to use "plain old bob" anyway, you may as well as encode interlaced and use a player that bobs on playback, such as VLC - and VLC can also Yadif on playback (apparently).

That way you don't waste bits on those bobbed scanlines.

David

I agree. Also if you have an Nvidia card, the purevideo hardware de-interlacer is very good (compared to bob anyway) and runs off your gpu on the fly.