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25fps- still euro standard?


johngooch

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At least for SD we broadcast 50i, equivalent timecode 25fps. TV-Shoots in HD are usually shot in 25p. Cinema is sometimes shot @ 24p.

Still some old TV-sets are clocked by the 50hz AC power system.

I never had a European production shot at anything but 25 (or 24 for Cinema). At least regarding to timecode. Not long ago, in the Betacam days, the video isself was 50i and nothing but.

Afaik 23,98 makes it somehow easier to convert to NTSC 29.97fps (Actually 30 without a color reference frame every while)

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" Afaik 23,98 makes it somehow easier to convert to NTSC 29.97fps "

HUH??

???

23.98 (actually 23.976) is the same .1% pulldown (slower) from 24.000 as 29.97 is from 30.000.

" (Actually 30 without a color reference frame every while) "

Huh? ???

:wacko:

HUH??

I don't even understand that...

what color reference frame??

:(

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John,

A question.... What is the delivery format? Though 25fps is standard in the 50Hz world, a project shot ON NEGATIVE in the 50Hz world for American post and delivery can be achieved by setting the 24fps FILM camera's shutter angle to 172.8 degrees (have 'em lock that puppy down!) with sound reference at 30fps. This works for FILM only, I've no experience shooting HD in Europe for American delivery.

Jay

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" Afaik 23,98 makes it somehow easier to convert to NTSC 29.97fps "

HUH??

I don't even understand that...

what color reference frame??

:(

Regarding "somehow easier", that was an educated guess. Why does 23,98 exist? Since we in the 25/50 world hardly come in contact with fractional framerates, (exept maybe rate conversion of foreign source material in broadcast houses.) maybe you new-world people can explain.

To the color reference frame within NTSC I hope I remember things right from TV school 10 years ago. We had a lesson on NTSC but only PAL was part of the exam ;)

Todays frame rates bring us all the way down to the history of electricity. When power line companies established a power standard in the beginning of the last century, they chose a 60Hz DC frequency on the American continent, while in Europe, they ended up at 50hz. Later when televison was invented, in the first half of the last century, they used 60i in America and 50i in Europe, so that TV sets could use the power source as a v-sync. To avoid flickering on the shortly afterglowing catode ray tubes a higher frequency than the 30/25 fps was needed but to avoid the high and expensive video-bandwidth of a 60/50-full-frame-signal they decided to only transmit every second line of the picture (at least in Europe). Some decades later, in America, they wanted to also transmit color over the same signal, but the old black&white tv-sets had to still be usable. The NTSC signal was born ,introducing a "dropped" frame every half minute or so, containing no picture-information, but some kind color reference information. so, 30fps -1frame every 33s ends up to 29,97fps The problem with this was, that due to changes in the athmosphere (weather) the color reference could become somewhat outdated before a new ref was transmitted. The reason, for the teasing abrevation "never the same color" for NTSC. Compare to https://groups.googl...3089c4d53?hl=fi

A few years later european developers could learn from the difficulties with NTSC and NTSC implemented the reference frequency for the color subcarrier oscillator on a short burst on the back proch of every horizontal line.

Edit: Reresearching the topic I realize, that I've obviously mixed up some stuff. The "dropped" frame just refers to a timecode that was adapted to a slightly pitched video bandwidth. The latter was neccessary to avoid interference of the chroma and audio signals with the luma signal. Also, the color reference burst on the back porch was not introduced with pal, but is a part of NTSC too.

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John,

A question.... What is the delivery format? Though 25fps is standard in the 50Hz world, a project shot ON NEGATIVE in the 50Hz world for American post and delivery can be achieved by setting the 24fps FILM camera's shutter angle to 172.8 degrees (have 'em lock that puppy down!) with sound reference at 30fps. This works for FILM only, I've no experience shooting HD in Europe for American delivery.

Jay

Job is in the vapor phase now. delivery is not determined but it is not for broadcast. Multi media display to travel to both Europe and North America. Just wanted to see if there was common ground and of course there is not. I am not putting together, just wanted to answer some of the questions of a very un-educated client.

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The previous description of color television is only partly correct. The statement about dropping frames should be disregarded. Please refer to "Technical Details" in the Wikipedia entry for NTSC:

http://en.wikipedia.org/wiki/Ntsc

The short version is that black and white TV in our corner of the world was 30 frames a second (with two fields making up each frame) until the implementation of color television. In order to accommodate the color signal, the frame rate was slowed down by a tenth of one percent which then made it 29.97 frames per second. This was close enough to 30fps that it was backward compatible with black and white TV sets which could be adjusted slightly (sets used to have a "vertical hold" knob on the front) to properly receive the broadcast. signal.

Forget any discussion about dropping frames. Even "drop frame" time code doesn't drop any frames -- it only counts them differently (which is where the confusion above likely comes from).

In order to telecine (transfer film to video) film shot at 24fps to NTSC video, the film playback rate is slowed down by a tenth of one percent to accommodate the frame rate of video (i.e. You can't transfer 24 complete frames onto 29.97 frames since we can't use fractional frames). By slowing down the film by a tenth of a percent, you can then transfer every 24 frames onto every 30 frames by creating 6 additional frames derived from a pattern of fields from adjacent frames every four frames. This field pattern and concurrent speed change is where the term "2:3 pulldown" comes from. 2:3 referring to the field pattern used to create the additional frames and pulldown referring to the one tenth of one percent speed reduction.

The easiest way to wrap your brain around some of this is to think in terms of "film speed" and "video speed." Therefore, 24fps is a "film speed," and 23.976 (one tenth of one percent slower) is a "video speed."

Since this speed difference means that the actual program time is a tad different from the time code count, drop frame time code was introduced. Drop frame time code is used by broadcasting facilities because they need an accurate time code clock (for obvious reasons). Drop frame time code DOES NOT drop any frames! It only counts them differently (every minute it skips counting two frames except for every tenth minute). This counting method makes the time code readout match the actual running time of the program.

The reason 24 frames is now frequently used (and consequently, 23.976 for video) is because many people prefer the "look" of material acquired at this frame rate since it aesthetically simulates the motion picture look we are familiar with.

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What my CPF John just said...

" Why does 23,98 exist? "

" 23.98 (actually 23.976) is the same .1% pulldown (slower) from 24.000 as 29.97 is from 30.000. "

" introducing a "dropped" frame every half minute or so, containing no picture-information, but some kind color reference information. so, 30fps -1frame every 33s ends up to 29,97fps The problem with this was, that due to changes in the athmosphere (weather) the color reference could become somewhat outdated before a new ref was transmitted. The reason, for the teasing abrevation "never the same color" for NTSC. "

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" 23,98 exists to transcode to 29,97 "

both are non-integer speeds .1% slower than real time.

they divide the same "slightly longer seconds" containing whole frames (24 whole frames, and 30 whole frames), but of course they divide by 24 and 30. They match up at the :00 frame, and match up in time -but not number- at the 12/24th and the 15/30th frames

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