[FFmpeg-user] Proper way to reverse PAL Speed up?

Carl Eugen Hoyos cehoyos at ag.or.at
Sun Feb 3 15:18:49 CET 2013

Bernd Butscheidt <bbutscheidt <at> yahoo.de> writes:

> I tried to find a way to reverse the PAL Speed up used 
> by television broadcasts back to ntsc film using recent
> ffmpeg. The HD-Television stream like the one used in 
> the example given below are actually broadcast with 50fps.

(Disclaimer: It is absolutely possible that you know much 
more than I do about how this recording was actually 
produced, I can only write what I think - and I think 
that there are some indications that I am correct, but 
who knows.)

Afaict, the sample you uploaded was recorded with a 50Hz 
camera: Either with a camera that records 50 progressive 
frames per second, or a camera that records 50 (true) 
fields per second, some post-processing was used to create 
50fps progressive content (and I would expect that the 
camera has a higher horizontal resolution than 720 lines 
in this case) out of this 50 fields.

If you need 25 / 24 / 23.9 fps output, you will have to 
drop frames or you have to radically (by a factor of two) 
change the playback speed of the stream.

Note that I am not saying that there is anything wrong 
with your command line (it of course drops half of the 
input frames but that simply may be what you want) but 
given that I don't understand what you want to achieve, 
it is difficult for me to make suggestions.

If you record a movie - I do that regularly with a very 
similar setup and very similar TV provider(s) as you - 
on the same channel the situation is of course different.
But in this case, the safe variant is to specify -r 25 
since you usually don't know if the sound was speed up 
in post-processing or not (so there is a good chance you 
damage the sound with your complicated filter chain).
(This is of course different if you actually hear that 
the sound has been tampered with, in any case I would 
have expected that the output framerate hast to be 
exactly 24fps and not 24000/1001).

Carl Eugen

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