Why 24000/1001 instead of 24 fps ?

[seandarcy]

I'm in NTSC land . All the sources are 30000/1001. The movies started out as 24 fps, and were re-encoded for NTSC. But TV's can now display 24. Why is it recommended ( at least on ffmpeg user ) to reencode the dvd sources to 24000/1001 ? As long as your TV takes 24, why not return to the original 24 framerate ?

sean

[Cary Knoop]

Because old habits die hard.

[sneaker_ger]

If you return to the original 24.000 you need to:
- re-encode the audio (quality loss)
- may experience compatibility problems

Now compared to those downsides what are the upsides? A human won't notice the difference between 24.000 and 24/1.001 fps.

[Springnow]

It's meaningless to differentiate 24000/1001 and 24fps. Essentially, there is no substantial difference between them. Leave it alone if it can successfully playback on your TV or other devices.

[Ghitulescu]

I'm in NTSC land . All the sources are 30000/1001. The movies started out as 24 fps, and were re-encoded for NTSC. But TV's can now display 24. Why is it recommended ( at least on ffmpeg user ) to reencode the dvd sources to 24000/1001 ? As long as your TV takes 24, why not return to the original 24 framerate ?

sean

Are you sure your TV could do 24fps?
Specs, in particular recent ones, are written not only by people having little understanding of technology but also with the inteneded goal of seducing the customers.
Although all flat-TV panels since their appearance could do 60Hz (for being internally driven at that rate), I have rarely seen the 59.94 in their specs, let alone 60/1.001.
Therefore the question: are you sure your TV really means 24fps or it could also mean 24/1.001 or, worse, not even care, and resynching the frames once in a while (every 1001 of them :) )?

[seandarcy]

But I'm already reencoding:

ffmpeg -i ... -r ???? -c-v libx264 ....

If I "leave it alone" it'll keep the 30000/1001 and spit out lots of dupes, especially if it's soft telecined, as usual.

[seandarcy]

The source is 30000/1001. I agree you wouldn't change the framerate if the source were 24000/1001 .

[Cary Knoop]

The source is 30000/1001.
If the source is 30p why would you want to change it? Unless it is a clip to be part of a 24p video keep it the way it is.

[Asmodian]

If I "leave it alone" it'll keep the 30000/1001 and spit out lots of dupes, especially if it's soft telecined, as usual.

If you undo the soft telecene you get 24/1.001 fps, not 24. This is why you use 24/1.001 instead of 24. If you used 24 exactly you would still have one of those dupes left every 1001 frames.

On a NTSC VHS, DVD, or bluray a "24 fps" move has a true source frame rate of 24/1001 because of historical reasons. :p

[kolak]

Are you sure your TV could do 24fps?
Specs, in particular recent ones, are written not only by people having little understanding of technology but also with the inteneded goal of seducing the customers.
Although all flat-TV panels since their appearance could do 60Hz (for being internally driven at that rate), I have rarely seen the 59.94 in their specs, let alone 60/1.001.
Therefore the question: are you sure your TV really means 24fps or it could also mean 24/1.001 or, worse, not even care, and resynching the frames once in a while (every 1001 of them :) )?


Modern TVs do /1001 fps with no problems as well as 24p. Old ones may have problem with it, but this will be related to quite old TVs.

[seandarcy]

If you undo the soft telecene you get 24/1.001 fps, not 24. This is why you use 24/1.001 instead of 24. If you used 24 exactly you would still have one of those dupes left every 1001 frames.

On a NTSC VHS, DVD, or bluray a "24 fps" move has a true source frame rate of 24/1001 because of historical reasons. :p

Gotcha. Thanks.

[huhn]

BTW. 24 hz is used on BD too and obviously it is part of the spec there is even one disc where i know it is used.
i haven't found a single TV that doesn't support 24p and 23p it's just rarely used.

windows XP can only do 24p and not 23p so proper old TV shouldn't have any issues with that.

[kolak]

There are quite many BD discs done at 24p, opposite to 23.976p.
23.976p is related to broadcast- most outdated and legacy form of content delivery.
Modern TVs are not the problem here at all.

[Asmodian]

But none of those are telecined into 29.97 or 30 fps video. :p

24 fps on Blu-ray will use 24p.

[sneaker_ger]

You can find both 24/1.001 fps and 24.000 fps Blu-Rays on the European market. But on the US market 24.000 fps is very seldom - I assume similar for streaming. Not sure about Korea/Japan. So 24.000 fps is overall much less tested on all equipment (TVs, audio receivers, USB/streaming sticks).

[benwaggoner]

You can find both 24/1.001 fps and 24.000 fps Blu-Rays on the European market. But on the US market 24.000 fps is very seldom - I assume similar for streaming. Not sure about Korea/Japan. So 24.000 fps is overall much less tested on all equipment (TVs, audio receivers, USB/streaming sticks).
24p is more common in streaming, since most providers just stick with whatever fps the content arrives at to avoid messing with the audio and any time-based metadata.

More and more sources are actually 24p, and thus published as such. Still a minority, though. More common with movies than broadcast.