[FFmpeg-user] Deinterlace and change framerate with -vcodec copy

[Peter Bašista]

On Mon, May 23, 2011 at 9:18 PM, Andrew Berg wrote:
>> I have spotted this sentence in the manual page of ffmpeg:
>>
>> "... but deinterlacing introduces losses."
>>
>> which was enough for me to give it up.
> Yadif is very good. It's also worth mentioning that deinterlacing is
> necessary to display interlaced content on a progressive display. Media
> players and HDTVs do this during rendering. Technically, deinterlacing
> filters irreversibly alter the video, but only very poor quality filters
> hurt quality, so such wording in the man page is misleading. You can
> search this list (and the MEncoder-users list) for tons of discussion on
> deinterlacing. In short, it's almost always a good idea to deinterlace
> with a high-quality filter like Yadif.

All right, I take that into account. But I will seriously consider
deinterlacing the video, encoding it and storing it deinterlaced only
very occasionally.

My primary objective is to avoid reencoding whenever possible. I will
rather keep using the deinterlace filters during playback.

>> So, I will try to summarize and I will welcome any corrections:
>>
>> Deinterlacing:
>> 1) is only possible with reencoding
> Video filters require decoding; it is not necessary to reencode the
> changed video. In most cases, you will want to encode the uncompressed
> video, but it's an important distinction - filters can be applied
> losslessly when rendering instead of encoding.

Then let me correct myself: Deinterlace video filters:
1) require video decoding
2) can only be applied to uncompressed video fields / frames

This means that unless you want the uncompressed video, you will have
to encode it afterwards.

>> 2) always introduces losses
> High-quality filters introduce very minimal loss.

I'll keep that in mind. Would it be okay to say:

Deinterlace video filters:
3) may introduce only a very minimal losses
4) but they are never lossless

> In any case, be sure to change the frame rate to 24000/1001 fps instead
> of 24fps.

Can you explain why?

Here:

http://avisynth.org/mediawiki/AssumeFPS

I have read that according to some standards (NTSC, PAL ... maybe some
others), fps is required to be specified as a ratio. But why
24000/1001 and not 24000/1000?

> Also, you might need to adjust the samplerate of the audio if
> the original was adjusted (which I would assume is the case, but I've
> never been in PAL land). It /might/ be possible to make your audio sync
> up untouched with container options, but I'm not sure how to go about
> doing that.

Thank you for reminding me about that. I know there might be issues
with V/A sync. But I suppose they can be handled with a little effort.

The main problem (change the video frame rate without changing the
total number of frames), unfortunately, still remains unsolved.

Peter Basista