Original is 29.97, compressed to an mp4 is 23.976

Hello,

My original master file is 29.97, I made an .mp4 from it for the web but forgot to change the frame rate to 29.97, so it made it as 23.976.

The file is over an hour long, so I only looked through sections and it seemed ok, but could there be glitches throughout due to the framerate change?

I'd rather not create the mp4 again but if I must, I must.

Thanks

Allow me to skip the NTSC decimals. (Read 30 as 29.97, 24 as 23.976, 60 as 59.94, if you must.)

If the original master file is progressive 30, so please do call it 30p, then your 24p was probably extracted from it like so:

Keep the first frame.
Keep the next frame.
Keep the next frame.
Keep the next frame.
Throw away the next frame.
Repeat from start.

This makes 4 frames for every 5 frames, to get the right speed. It discards 20% of your picture information. You get a nasty jumpy video, but clean.

If the original master file is interlaced 30, so please do call it 60i, then it contains fields captured 60 per second. Your 24p was probably wrenched from the 60i like so:

Keep the first field. Blur it to make a frame.
Throw away the next field.
Keep the next field. Blur it to make a frame.
Throw away the next field.
Throw away the next field.
Keep the next field. Blur it to make a frame.
Throw away the next field.
Keep the next field. Blur it to make a frame.
Throw away the next field.
Throw away the next field.
Repeat from start.

This makes 4 frames for every 10 fields, to get the speed right. But since they're made from just 4 of the 10 fields it's discarded 60% of your picture information. You get a nasty jumpy video with aliasing artifacts.

FCP7 does even worse violence to make the 60i into 24p:

Keep the first field. Blur it to make a frame.
Throw away the next field.
Keep the next field. Blur it to make a frame.
Throw away the next field.
Keep the next field. Blur it to make a frame.
Throw away the next field.
Keep the next field. Blur it to make a frame.
Throw away the next field.
Throw away the next field.
Throw away the next field.
Repeat from start.

I think the web streamer would play your 30p or 60i decently. I don't know how it will play the various 24p monsters described above.

Dennis Couzin
Berlin, Germany

i'd say watch the file though for a few minutes, in particular areas with rapid motion
how does it look?


nick

A problem with that approach is that different players will play 24p differently. Let him play it on the most horrible, so the two horribilities add.

Dennis Couzin
Berlin, Germany

Dcouzin,

You're some sort of mad genius, thanks for the details.

I made the mp4 in Adobe Media Encoder from a master export in FCP7 "current settings", it may have even been 60i, I just can't remember right now.

When I watched pieces it seemed fine, obviously motion was not as smooth at 23.976 but maybe I'm crazy I actually think it added to the final piece by giving it a faux film like motion, instead of the smooth soap opera feel of the original.

If client has any issues, I'll just re do it but for now c'est la vie.