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

[Andy Civil]

On 2013-07-26 4:51 AM, Carl Eugen Hoyos wrote:
> 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.)

(Deliberate. Analysis unnecessary distraction.)

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

Because I went to the trouble of supplying it with 60fps so that it could.

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

Because DVDs are normally interlaced, interlaced video is better*, and I gave it 
enough input information to produce interlaced.

(* not normally, of course, but within the constraints of what is a valid 
DVD-video stream.)

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

Ha ha - touché! I mean that the days when interlacing was a viable alternative 
to compression for data rate reduction are over, and the only need we have for 
interlacing now are the embarrassing hold-overs from those days :-) like the 
DVD-video specification.

>> 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

Well, I gave my reasoning and my experience bears it out, so forgive me sir if I 
consider it the truth until a seed of doubt can be sown. In my opinion, the only 
way that interlaced could end up looking worse, would be if the data rate was 
inadequate and the compression (harder on interlaced content because there's 
more information) couldn't keep up.

> (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).

All the content came from my video camera - this isn't a pirated movie - and 
there are no duplicated frames at all.

>
>> 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.

Sadly, you're right. According to "gspot" the output is interlaced, but it's 
actually 30p. The flags are set, but the actual frames are progressive.

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

I will follow up with another post asking for hints as to the form of the 
command. For this I will definitely include your famous "uncut console output" 
so that you can see what I'm starting from.

Thank you.

--
Andy