ffmpeg: Exactly what does the -top option do?

[dlflannery]

I use gui4ffmpeg as a front end to ffmpeg. The -top command line option for ffmpeg has to do with TFF, BFF or "automatic field selection" (for values 1, 0, and -1). I had to use "-top 1" for one re-encode of an interlaced mpeg that had mixed TFF/BFF according to gspot.

It worked but I don't know exactly what it did. The documentation is very sparse. The *** online documentation ** does not even mention this option. You get a line or two of help using command line "ffmpeg -h".

I've searched forums and gmane and have not found any detailed explanation of what this switch does in terms of decoding the input and/or encoding the output mpegs.

Can anyone tell me?
Thanks

[GTRBudda]

I think it's like this:

-top 1 sets output to top field first
-top 0 sets to bottom field first
-top -1 senses what the input is and adjusts for it

This is from the Gui4FFMpeg help file (an actual help file, GUI4FFMPEG_ENG.HLP, not the online docs. I wish I could remember where I found it, maybe Google....):

-top top=1/bottom=0/auto=-1 field first

[dlflannery]

Thanks GTRbudda.

I'm still hoping for more detail. Anyone ????

[GTRBudda]

Glad to help.
Duh, the help file is in the download zip. some how I thought they were seperate. Oh, and I think you have to put "-ildct" and/or "-ilme" before it, to set the ouput to interlaced. This is a script I use to make Mpeg2 compatible with the output from my recorder:

"C:\Program Files\gui4ffmpeg\ffmpeg.exe" -i "c:\path\to\file.flv" -hq -target ntsc-dvd -bf 2 -ildct -ilme -top 1 -dc 10 -b 6500 -maxrate 8000 -aspect 4:3 -s 656x448 -padright 32 -padleft 32 -padtop 16 -padbottom 16 -acodec ac3 -ab 256 -ac 2 -mbd 2 -qmin 2 -async 1 -y "c:\path\to\file.mpg"