Sox Pal->Ntsc conversion?

Foofaraw · 16th September 2012, 02:57

I was looking to convert a PAL sound to NTSC, and it was suggested I use Sox, and I found this snippet:

sox in.wav output.wav speed 0.95904

And that sounds right, except the output file grows in duration, which is not what I want.

So I'm guessing I should use the -pitch argument instead - however I have no idea what value is the correction one - anybody know what it should be?

Selur · 16th September 2012, 18:31

It's unclear what you want, if you have a video stream and you do a 'slow down' from 25fps to 24fps the duration changes, so should the duration of your audio if it is ment to stay synch.
Since you do not seem to want to change the audio length it is unclear what you want sox to do with your audio stream,...

sneaker_ger · 16th September 2012, 18:55

According to his post in the eac3to thread he really just wants to change the pitch. PAL speedup results in a pitch change of 70.67 cents, but I'm not 100% sure if you can just use -70.67 for the pitch parameter to reverse the effect - maybe someone else can explain.
Though I support Selur's suggestion to slowdown both video and audio to get the original playback speed and pitch. This can be done losslessly for video.

Foofaraw · 16th September 2012, 19:46

Quote:

Originally Posted by Selur

It's unclear what you want, if you have a video stream and you do a 'slow down' from 25fps to 24fps the duration changes, so should the duration of your audio if it is ment to stay synch.
Since you do not seem to want to change the audio length it is unclear what you want sox to do with your audio stream,...

As I wrote, I want to change the audio from the PAL speed to the NTSC speed.

Quote:

Originally Posted by sneaker_ger

According to his post in the eac3to thread he really just wants to change the pitch. PAL speedup results in a pitch change of 70.67 cents, but I'm not 100% sure if you can just use -70.67 for the pitch parameter to reverse the effect - maybe someone else can explain.
Though I support Selur's suggestion to slowdown both video and audio to get the original playback speed and pitch. This can be done losslessly for video.

Hi sneaker_ger.

I didn't want to touch the video because I thought that would mean re-encoding, plus it would take 5000% longer than just processing the audio.

But you are saying one can do this losslessly for video?

Didn't know that.

As for using -70.67 I'll try that as soon as I have finished my pizza

Foofaraw · 17th September 2012, 01:17

Well, it seems to accept -70.67 but it doesn't sound quite slow enough.

And sneaker_ger based on your suggestion of video, I tried putting video and audio in an mkv, and change the video playback speed - it did appear to be in sync - though the subtitles were now out of step. If I have to OCR them and resync it becomes a bigger job :-/

Oh well.

sneaker_ger · 17th September 2012, 06:12

OCR is not necessary. You can change the subtitle speed in mkvmerge GUI as well, by selecting the subtitle track and entering the following in the "Stretch by" field:
25 -> 23.976: 25025/24000
25 -> 24.000: 25/24
23.976 -> 25: 24000/25025
24.000 -> 25: 24/25

I hope I got the numbers correct. Otherwise you could also re-time the subtitles with programs like BDSup2Sub.

Foofaraw · 18th September 2012, 01:27

Quote:

Originally Posted by sneaker_ger

OCR is not necessary. You can change the subtitle speed in mkvmerge GUI as well, by selecting the subtitle track and entering the following in the "Stretch by" field:
25 -> 23.976: 25001/24000
25 -> 24.000: 25/24
23.976 -> 25: 24000/25001
24.000 -> 25: 24/25

I hope I got the numbers correct.

Curious, I tried adding that to the field, but the resulting mkv now displays its duration as one third of the original length!
(and doesn't play)
Hm..

sneaker_ger · 18th September 2012, 07:13

Stretching a single track should in no way change the duration of the complete file by a third. Re-check and make sure that you're stretching the correct tracks.

Foofaraw · 19th September 2012, 02:18

Quote:

Originally Posted by sneaker_ger

Stretching a single track should in no way change the duration of the complete file by a third. Re-check and make sure that you're stretching the correct tracks.

I would assume it only stretches the subtitle track not the video?

Anyway, in mkvmerge I click on a S_VOBSUB track (I only keep one), chose the "Format Specific options" and enter something like "24000/1001" in the "Stretch by" field - and that produces an mkv with a wildly different playback length.

Asmodian · 19th September 2012, 20:42

25001/24000 not 24000/1001

Foofaraw · 20th September 2012, 00:01

Quote:

Originally Posted by Asmodian

25001/24000 not 24000/1001

The numbers make no sense to me. Could you explain how you arrived at 25001/24000?

Its much better, but not quite right, by the end it has drifted by about 4 seconds.

Asmodian · 20th September 2012, 01:14

I just copied what sneaker_ger stated. Are you going to 24000/1001 or 24 fps?

I assume it is just the ratio you want them slowed by.

[START FPS] = [END FPS] * X

Foofaraw · 20th September 2012, 01:38

Quote:

Originally Posted by Asmodian

I just copied what sneaker_ger stated. Are you going to 24000/1001 or 24 fps?

I assume it is just the ratio you want them slowed by.

[START FPS] = [END FPS] * X

Source was originally 25. In Mkvmerge I set the FPS for the video track to 24000/1001 (which then matches the new audio)

Using "25001/24000" as you suggested (sorry Sneaker_ger I'm getting confused over these numbers) on the subtitle track, means it starts out well enough in sync, but it drift over time, showing up too late.

Asmodian · 20th September 2012, 01:52

Hmm, well 25 / (24000/1001) = 25025/24000 not 25001/24000 so that is probably it.

Foofaraw · 20th September 2012, 01:59

Quote:

Originally Posted by Asmodian

Hmm, well 25 / (24000/1001) = 25025/24000 not 25001/24000 so that is probably it.

I tried actually calculating it.
25001/24000=1.041708333333333

Whereas

25/23.976=1.042709376042709

So not the same. I tried using 1.042709376042709 instead and that worked

Now the subs didn't drift.

This is black magic

Asmodian · 20th September 2012, 02:07

It really isn't black magic, sneaker_ger just forgot to multiply the 1 during 1001*25.

1.0427083333333333333333333333333 is more correct.

Foofaraw · 20th September 2012, 04:31

How many decimals will it take?

Asmodian · 20th September 2012, 06:48

Just use 25025/24000 or 1001/960.

But your 25/23.976 is only 3.6 ms slow every hour so you might not need to worry about it.

Foofaraw · 20th September 2012, 15:11

sounds good

sneaker_ger · 24th September 2012, 12:05

Ah, yes, Asmodian is correct, of course. I did forget the 1...
I corrected my post.

And you can put those fractions directly into the field, no need to calculate them to a float.

16th September 2012, 02:57	#1 \| Link
Foofaraw Registered User Join Date: Apr 2004 Posts: 126	Sox Pal->Ntsc conversion? I was looking to convert a PAL sound to NTSC, and it was suggested I use Sox, and I found this snippet: sox in.wav output.wav speed 0.95904 And that sounds right, except the output file grows in duration, which is not what I want. So I'm guessing I should use the -pitch argument instead - however I have no idea what value is the correction one - anybody know what it should be?

16th September 2012, 18:31	#2 \| Link
Selur Registered User Join Date: Oct 2001 Location: Germany Posts: 7,631	It's unclear what you want, if you have a video stream and you do a 'slow down' from 25fps to 24fps the duration changes, so should the duration of your audio if it is ment to stay synch. Since you do not seem to want to change the audio length it is unclear what you want sox to do with your audio stream,... __________________ Hybrid here in the forum, homepage, its own forum

17th September 2012, 06:12	#6 \| Link
sneaker_ger Registered User Join Date: Dec 2002 Posts: 5,565	OCR is not necessary. You can change the subtitle speed in mkvmerge GUI as well, by selecting the subtitle track and entering the following in the "Stretch by" field: 25 -> 23.976: 25025/24000 25 -> 24.000: 25/24 23.976 -> 25: 24000/25025 24.000 -> 25: 24/25 I hope I got the numbers correct. Otherwise you could also re-time the subtitles with programs like BDSup2Sub. Last edited by sneaker_ger; 24th September 2012 at 12:04.

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16th September 2012, 18:55	#3 \| Link
sneaker_ger Registered User Join Date: Dec 2002 Posts: 5,565	According to his post in the eac3to thread he really just wants to change the pitch. PAL speedup results in a pitch change of 70.67 cents, but I'm not 100% sure if you can just use -70.67 for the pitch parameter to reverse the effect - maybe someone else can explain. Though I support Selur's suggestion to slowdown both video and audio to get the original playback speed and pitch. This can be done losslessly for video.

17th September 2012, 01:17	#5 \| Link
Foofaraw Registered User Join Date: Apr 2004 Posts: 126	Well, it seems to accept -70.67 but it doesn't sound quite slow enough. And sneaker_ger based on your suggestion of video, I tried putting video and audio in an mkv, and change the video playback speed - it did appear to be in sync - though the subtitles were now out of step. If I have to OCR them and resync it becomes a bigger job :-/ Oh well.

18th September 2012, 07:13	#8 \| Link
sneaker_ger Registered User Join Date: Dec 2002 Posts: 5,565	Stretching a single track should in no way change the duration of the complete file by a third. Re-check and make sure that you're stretching the correct tracks.

19th September 2012, 20:42	#10 \| Link
Asmodian Registered User Join Date: Feb 2002 Location: San Jose, California Posts: 4,456	25001/24000 not 24000/1001

20th September 2012, 01:14	#12 \| Link
Asmodian Registered User Join Date: Feb 2002 Location: San Jose, California Posts: 4,456	I just copied what sneaker_ger stated. Are you going to 24000/1001 or 24 fps? I assume it is just the ratio you want them slowed by. [START FPS] = [END FPS] * X

20th September 2012, 01:52	#14 \| Link
Asmodian Registered User Join Date: Feb 2002 Location: San Jose, California Posts: 4,456	Hmm, well 25 / (24000/1001) = 25025/24000 not 25001/24000 so that is probably it.

20th September 2012, 02:07	#16 \| Link
Asmodian Registered User Join Date: Feb 2002 Location: San Jose, California Posts: 4,456	It really isn't black magic, sneaker_ger just forgot to multiply the 1 during 1001*25. 1.0427083333333333333333333333333 is more correct.

20th September 2012, 04:31	#17 \| Link
Foofaraw Registered User Join Date: Apr 2004 Posts: 126	How many decimals will it take?

20th September 2012, 06:48	#18 \| Link
Asmodian Registered User Join Date: Feb 2002 Location: San Jose, California Posts: 4,456	Just use 25025/24000 or 1001/960. But your 25/23.976 is only 3.6 ms slow every hour so you might not need to worry about it.

20th September 2012, 15:11	#19 \| Link
Foofaraw Registered User Join Date: Apr 2004 Posts: 126	sounds good

24th September 2012, 12:05	#20 \| Link
sneaker_ger Registered User Join Date: Dec 2002 Posts: 5,565	Ah, yes, Asmodian is correct, of course. I did forget the 1... I corrected my post. And you can put those fractions directly into the field, no need to calculate them to a float.