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Best compression for TV broadcast?


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#1 Fran Tilley

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Posted 15 July 2012 - 02:14 AM

Hi guys, I am a recently graduated directing student and wasn't taught about the in depth technical aspects of broadcasting frame rates, NTSC and PAL. So please bear with me!

My film will be broadcast on TV but I need to send the file to the TV station online (its due on monday in a foreign country)- do you know a compression setting that I can use for decent broadcast-able footage yet is a good enough size to send online? I am only familiar with H.264 for youtube and vimeo.

It is approx 13 minutes- when I compress will have to change the 23.98 fps of NTSC to PAL at 25 fps in compressor (I did a trial and the playback was okay). It was my first time shooting and was just a trial project that was meant to be web based. That's why I didn't plan the shoot for it to be broadcast on TV and on the PAL system but it gained some interest cos of the topic and would really appreciate if anyone could help me. I have compressor..

Thanks!!
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#2 Keith Walters

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Posted 15 July 2012 - 04:09 AM

Hi guys, I am a recently graduated directing student and wasn't taught about the in depth technical aspects of broadcasting frame rates, NTSC and PAL. So please bear with me!

My film will be broadcast on TV but I need to send the file to the TV station online (its due on monday in a foreign country)- do you know a compression setting that I can use for decent broadcast-able footage yet is a good enough size to send online? I am only familiar with H.264 for youtube and vimeo.

It is approx 13 minutes- when I compress will have to change the 23.98 fps of NTSC to PAL at 25 fps in compressor (I did a trial and the playback was okay). It was my first time shooting and was just a trial project that was meant to be web based. That's why I didn't plan the shoot for it to be broadcast on TV and on the PAL system but it gained some interest cos of the topic and would really appreciate if anyone could help me. I have compressor..

Thanks!!

How big is your original file and what format is it in?
The answer is simply that you should only compress it down to the biggest size that you can send, or they can receive. The more bits, the better the quality, simple enough. Most compression software gives you the option of setting the final file size in advance. As for the format, well, lots of commercials have been recorded as MPEG4 on a 5D...
However it also depends on the quality of your original file, above a certain data rate, it may not make any worthwhile difference.
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#3 Fran Tilley

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Posted 15 July 2012 - 05:23 AM

How big is your original file and what format is it in?
The answer is simply that you should only compress it down to the biggest size that you can send, or they can receive. The more bits, the better the quality, simple enough. Most compression software gives you the option of setting the final file size in advance. As for the format, well, lots of commercials have been recorded as MPEG4 on a 5D...
However it also depends on the quality of your original file, above a certain data rate, it may not make any worthwhile difference.


Hi Keith,

Thanks for the suggestions. I haven't exported it yet but I am estimating 7GB as the 10 minute trial export I did was 6GB. It will be a quicktime .mov file. Would you have any suggestions as to what bit rates I should be aiming for in order to get a 500MB file? The receiver has a slow server so that would be the best compromise...

Also- what aspect ratio should I look at if converting from (NTSC) HDTV 1080i (16:9) to PAL? I will be converting it to PAL first using Apple ProRes 422 (LT) before I compress the file..
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#4 Chris Burke

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Posted 15 July 2012 - 07:41 AM

the file limit for lots of free file transfer sites is 2 gig. I would compress it to that size, again for maximum quality. keep it as a ProRes LT file and send that.
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#5 Keith Walters

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Posted 15 July 2012 - 07:45 AM

Hi Keith,

Thanks for the suggestions. I haven't exported it yet but I am estimating 7GB as the 10 minute trial export I did was 6GB. It will be a quicktime .mov file. Would you have any suggestions as to what bit rates I should be aiming for in order to get a 500MB file? The receiver has a slow server so that would be the best compromise...

Also- what aspect ratio should I look at if converting from (NTSC) HDTV 1080i (16:9) to PAL? I will be converting it to PAL first using Apple ProRes 422 (LT) before I compress the file..

Well, 13 minutes x 60 seconds = 780 seconds
500MB x 8 = 4,000 megabits
4,000 divided by 780 = 5.128 megabits/sec

As for the aspect ratio, if you mean actual CCIR PAL with a subcarrier and so on, as used for analog broadcasts in Europe, there is only one aspect ratio 4:3.
If by "PAL" you mean 25 pictures/sec digital, the aspect ratio is exactly the same as for "NTSC" HDTV, (but you really mean ATSC HDTV).
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#6 Fran Tilley

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Posted 15 July 2012 - 11:04 AM

Okay Chris- thanks I will aim for that using Keith's calculations for bit rate.

Keith- it is PAL that will be broadcast from South Africa. Again- I may be wrong but I believe it is the 25 fps version (I am still waiting for the reply from the TV station). That calculation has helped me with future knowledge and clarification on bitrates- again, much appreciated.
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#7 Phil Connolly

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Posted 15 July 2012 - 03:11 PM

Hi Fran

Most Broadcasters will tell you what file format and bit-rate they require. Its best just to stick to that. In the UK one of the standard delivery formats for SD is 50Mbit/s Mpeg-2. Generally they want all deliveries to be the same bit-rate/format so their are no issues with trans-coding. So even if there are more efficient codecs, mpeg-2 is still used a-lot in transmission.

Even if you can get similar quality with smaller files the broadcaster may specify a certain file size and you just have to stick to it. The BBC spec is very clear on whats required in the UK: http://www.bbc.co.uk...elevision.shtml

Maybe your broadcaster has a similar document for SD submission's.
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#8 Keith Walters

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Posted 15 July 2012 - 07:35 PM

Okay Chris- thanks I will aim for that using Keith's calculations for bit rate.

Keith- it is PAL that will be broadcast from South Africa. Again- I may be wrong but I believe it is the 25 fps version (I am still waiting for the reply from the TV station). That calculation has helped me with future knowledge and clarification on bitrates- again, much appreciated.

SA uses pretty much identical PAL to Europe, (25fps 4.43MHz subcarrier) and there aren't any digital transmissions, so your aspect ratio has to be 4:3. However I'd strongly recommend you leave your project in its original aspect ratio and let them work out how to display it.
Since it will only be displayed in PAL, 5Mb/s MPEG4 will be more than good enough for submitting it. You don't have to worry too much about format conversion, they will have all the necessary conversion software; you can even get freeware that does a perfectly adequate job. Most stations have a large collection of such software, so they have a chance that they can find at least one that can handle some of the "weirdo" cellphone video formats their Newsdesks get sent!
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#9 Keith Walters

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Posted 15 July 2012 - 07:51 PM

Hi Fran

In the UK one of the standard delivery formats for SD is 50Mbit/s Mpeg-2. .

50Mbit/s Mpeg-2?
50Mbit/s is the bit rate for DV (SD digital Betacam), which is more or less Motion JPEG.
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#10 Daniel Smith

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Posted 16 July 2012 - 03:41 AM

Digibetas are generally used for capture and intermediate storage in the broadcasters I've worked for, for standard definition applications. HDCAM-SR for most HD, or DNxHD, as many more people are using EVS for studio capture/insert playback.
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#11 Phil Connolly

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Posted 17 July 2012 - 03:21 PM

Yarp, 50Mbs Mpeg-2. In the Uk most delivery is still on tape Digi-Beta for SD and Hdcam-SR for HD. But more broadcasters are taking files, particularly for commercials and music videos etc..

50Mbs is good enough quality to give the video a decent chance of surviving re-compression down to 2-3Mbs for transmission. Tape deliveries are cached to server for transmission and when I worked in transmission we 50Mbs for SD.
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