[FFmpeg-user] ntsc-dvd doesn't default to interlaced.

[Carl Eugen Hoyos]

Andy Civil <andycivil <at> gmail.com> writes:

> Short description: I'm moaning that the default output 
> for "ntsc-dvd" is progressive, even if I give it 
> enough information to make it interlaced.

> c:\ffmpeg\bin\ffmpeg -i E:\temp\2013-06-07-hdp.mp4 
> -target ntsc-dvd -acodec mp2 -ac 2 -b:a 128000 
> output-dvd.mpg

(Complete, uncut console output missing.)

Nothing about this command specifies that your input 
is interlaced so why on earth should FFmpeg use 
interlaced encoding (that of course hurts 
compression)?

Or in other words: You did not give enough information 
to FFmpeg that you want interlaced content, so how 
should it guess?

[...]

> I can see a day when interlacing is pointless, 
> when all CRT displays are on the scrap

I use a CRT (all the time) and I certainly don't 
want interlaced content.

[...]

> a video of 30fps interlaced (60 fields per second) 
> does indeed look better than a straight 30p because 
> there is more temporal information

I consider this "wrong" (please consider that an 
euphemism).
If it is course perfectly fine that you disagree 
but please don't claim that this is a universal 
truth (especially since a large percentage of the 
60p material that can be used as input to your 
command line contains duplicated frames and 
never had more temporal information).

> I found that I had to specifically add the flags 
> -flags ildct+ilme to make it create a proper 
> interlaced video.

As such this is simply not true.
The flags make the encoder use interlaced algorithms 
which should only only be used on interlaced 
material (and which of course should be used for 
interlaced sources). In practice, it is often used 
for progressive material (and interlaced pictures 
were of course sometimes encoded without those flags).

Please note that FFmpeg supports producing 
interlaced content with the appropriate filter.

Carl Eugen