How To Do Audio frame rate conversion?

[kOoL tHuG]

So basically i have to Change the frame rate without changing either the pitch or the playback time

Hey Guyz. Basically i am doing a PAL (25 FPS) DvD to NTSC (29.97 FPS) Conversion. I figured out everything, froms menus to main movie and Subs. Only thing i couldnt't figure is audio speed up process. I have 448 kbps 5.1 AC3 (48000 KHZ) File with a runtime of around 180 Mins. I tried Besweet and Behappy. But i am not so much satisfied with the quality. I have heard that there r better solutions to this. I am not known to all this audio conversion process.

I heard of a way where i have to extract all the 6 channels to 6 Mono PCM Wavs. Do the process of converting them and putting them back together using Sonic Soft Encode.

But the biggest question. How do i do it?
Have i got a better way of doing it?
What exactly will i have to do so that i Change the audio frame rate without changing either the pitch or the playback time

Help regarding this will be truly appreciated. :thanks:

I am sorta noob in all this audio conversion. Plz hlp me out. :thanks: Again.

[smok3]

uhmm, if you don't have to change the playback time, then you don't have to process the audio at all...

[tebasuna51]

The audio don't have different frame rate in PAL or NTSC systems.
The ac3 (48 KHz) frame rate is 31.25 in PAL or NTSC systems.
Then never need change the audio for that.

The audio have a fix duration and only need change this duration (playback time) if you make a improper (but more simple) video conversion.

If you make the video conversion (25 -> 29.97) adding frames and preserving the playback time the audio don't need any change like smok3 say you.

[makikes]

kOoL tHuG, are you really doing a a 25 -> 29.97 or are you doing a 25 -> 23.976 conversion?

[frank]

Nonsens!

The real NTSC frame rate on DVD is 24000/1001=23.976 f/s.
The 29.97 fps makes video controller via the pull-down flag.

You have to convert the decoded WAVs, slow down from 25 to 23.976 fps (Besweet), and encode new.

Don't touch the pitch. Most studios are lazy and have not changed the pitch for PAL conversion.

[tebasuna51]

You have to convert the decoded WAVs, slow down from 25 to 23.976 fps (Besweet), and encode new.
Are you sure?
Read the first post:
"...without changing either the pitch or the playback time"
Don't touch the pitch. Most studios are lazy and have not changed the pitch for PAL conversion.
Are you sure?
For all languages?

[EuropeanMan]

Nonsens!

The real NTSC frame rate on DVD is 24000/1001=23.976 f/s.
The 29.97 fps makes video controller via the pull-down flag.

You have to convert the decoded WAVs, slow down from 25 to 23.976 fps (Besweet), and encode new.

Don't touch the pitch. Most studios are lazy and have not changed the pitch for PAL conversion.

so you're saying, convert the AC3 file to .WAV files, then re-encode from 25fps to 23.976, then convert the .WAV back to AC3?

[tebasuna51]

so you're saying, convert the AC3 file to .WAV files, then re-encode from 25fps to 23.976, then convert the .WAV back to AC3?

Please don't use video frame rate to talk about audio.
The ac3 (48 KHz) framerate for PAL or NTSC systems is 31.25.

If you slow down the video from 25 fps to 24000/1001 you need slow down also the audio (increase the duration) by a factor of 1001/960.

But you can delete some video frames (or add if go to 29.97) to maintain the duration (playback time) and now the audio can remain untouched.

[nautilus7]

Guys you are talking about different things. Tebasuna is aware of it, while EuropeanMan isn't. :D

EuropeanMan is talking about PAL<-->NTSC conversion, while Tebasuna51 about how many frames AC3 audio has per second based on the frame duration of AC3 audio (32ms duration each).

I believe KOol tHug wants to convert audio from 25 fps video to audio for 23,976 fps video, which means changing the duration. I can't understand why he mentions video framerates otherwise. He just isn't aware of what he really has to do... :p

If i am correct about what he needs, he can use eac3to to do that.

[makikes]

I agree nautilus7. That's how I do my own conversions: I slow down my audio tracks.

Bu kOoL tHuG is very precise about what he wants: "...without changing either the pitch or the playback time."

[tebasuna51]

Guys you are talking about different things. Tebasuna is aware of it, while EuropeanMan isn't. :D

EuropeanMan is talking about PAL<-->NTSC conversion, while Tebasuna51 about how many frames AC3 audio has per second based on the frame duration of AC3 audio (32ms duration each).

I believe KOol tHug wants to convert audio from 25 fps video to audio for 23,976 fps video, which means changing the duration. I can't understand why he mentions video framerates otherwise. He just isn't aware of what he really has to do... :p

If i am correct about what he needs, he can use eac3to to do that.

To avoid this kind of confusion I propose don't use this:
"convert audio from 25 fps video to audio for 23,976 fps video"
because a correct video conversion don't
"means changing the duration"

I propose something like this:
slow down (or increase duration) the audio to match the video 25 fps played at 23.976 fps
Here the video is not converted, only is slow down played then we need change the audio duration.

I know is more easy change the audio instead the video but isn't the correct way. When kOoL tHuG say:
"without changing ... the playback time"
I only can supose the video is correctly converted (same duration) and audio don't need change.

Maybe the question isn't correct because:
"without changing either the pitch or the playback time"
means, obviously, not change at all.

@kOoL tHuG

- eac3to change the pitch and the duration.

- Behappy have three methods:
Change only the pitch, only the duration or both pitch and duration like eac3to.

Try to change only the duration require a hard process without perfect output, is more easy change both (pitch and duration) with less artifacts and in some cases recover the original track.
You can try both methods with a problematic fragment and chose.

BTW there are commercial soft than can do with more quality the change duration only process. I test Audition with better results. The complete process can be:

1) Decode ac3 to wav. This step isn't determinant in quality then you can use BeLight-BeSweet, Foobar2000, BeHappy or eac3to all free. With eac3to you can use a official ac3 decoder (Nero 7 + plugin) not free.

2) Use an audio editor commercial, for instance Audition (349$), to do the change duration preserving pitch process.

3) Reencode to ac3. You can use the free Aften but, maybe, if you want more quality you can use Surcode (995$)

[EuropeanMan]

Ok...I know koolThug personally.

He has a movie DVD9, in PAL (from germany)...I've given him an assignment. To convert this movie to NTSC specifications.

From my understanding, to mux video & audio & subs (into DVD files via MuxMan)...video must be 29.976 via DGPulldown...this is why we were using the framerate terminology for the audio.

Now, here's the catch. I know there is a 4% speedup on the PAL disc. Therefore, kT needs to slow down the video & audio to get 29.976...this means adding frames.

Since the audio ALSO was sped up on the PAL, shouldn't there be pitch correction when slowing the audio down as well? Because from where I stand, a 3hour movie could be 3hours 7mins in NTSC...and if we kept the old audio, it would thus be STRETCHED causing distortion.

[staul62]

Hi EuropeanMan,

It seems to me that what your student needs to be doing is converting his 25 fps video to 23.976 fps, then adding appropriate flags to play the video at 29.97 fps. For this approach, you are correct that the audio must be slowed down. I use Belight/Aften for this - AC3 to AC3 direct.

I have a post in a thread in the forum listing my simple PAL - NTSC (film only) conversion steps, which work for me for PC playback. If it doesn't breach your assignment rules, I can post the thread link here :)

[tebasuna51]

It seems to me that what your student needs to be doing is converting his 25 fps video to 23.976 fps, then adding appropriate flags to play the video at 29.97 fps. For this approach, you are correct that the audio must be slowed down. I use Belight/Aften for this - AC3 to AC3 direct.

Can you make the audio conversion with BeLight/Aften if the ac3 is 5.1?

[smok3]

tebasuna51: what do you think is not correct? - that actually is the most correct way, simply each old frame is a new frame, they just run at different fps, no blending, jumping or other type of anomalies.

quick and dirty conversion i use sometimes for 23.x fps things:

assumefps(25, sync_audio=true)
ResampleAudio(48000)
# only tested when audio was 2ch

[tebasuna51]

tebasuna51: what do you think is not correct? - that actually is the most correct way, simply each old frame is a new frame, they just run at different fps, no blending, jumping or other type of anomalies.

Is easy and can be assumed, but isn't correct play a movie with different fps than was originally filmed.

You can use ChangeFPS or ConvertFPS instead AssumeFPS.

[Susana]

Well, most motion pictures are captured at 24 fps, and release on DVD at 23.976/25 fps speeding up or down the original audio track, but you already know it.

[tebasuna51]

Well, most motion pictures are captured at 24 fps, and release on DVD at 23.976/25 fps speeding up or down the original audio track, but you already know it.

Of course, we need difference two cases:

1) Recover a original audio from a 24 fps film bad converted (high pitch) to a PAL film. This is correct a previous problem.

2) Convert a original audio from my camera (PAL country) with video at 25 fps. This is the generic case, a conversion not a correction.

[staul62]

Can you make the audio conversion with BeLight/Aften if the ac3 is 5.1?

Yes you can. I've done so successfully

[tebasuna51]

Yes you can. I've done so successfully

Nope, I can't. I ask you, if you can, please put a log file to see the command line and soft versions.

[staul62]

Nope, I can't. I ask you, if you can, please put a log file to see the command line and soft versions.

Will do. This may take a day or so as the required files are at home.

[EuropeanMan]

Hi EuropeanMan,

It seems to me that what your student needs to be doing is converting his 25 fps video to 23.976 fps, then adding appropriate flags to play the video at 29.97 fps. For this approach, you are correct that the audio must be slowed down. I use Belight/Aften for this - AC3 to AC3 direct.

I have a post in a thread in the forum listing my simple PAL - NTSC (film only) conversion steps, which work for me for PC playback. If it doesn't breach your assignment rules, I can post the thread link here :)

thanks for the replies everyone...much appreciated. apparently kT doesn't take stock in replying here himself.

pal movie was at 25FPS progressive.
why would you want to go to 23.976?
and how would one set flags in CCE or otherwise?
because if i just CCEd the movie, i'd get 25fps, and then use
DGPulldown to get to 29.976 for NTSC specs.
is it BETTER to get to 23.976?...and if SO, can you please help in 2 areas:

1) what avisynth script would you use to get to 23.976? assumefps(23.976)? or... AND this would be split into 2 parts.
a) interlaced PAL video
b) progressive PAL video

2) how would one set a flag to show 29.976 without having to go thru DGPulldown...because from MY knowledge, CCE outputs an mpv file...DGP gives me m2v file, which any DVD Authoring software can thus use (along with the requisite audio, subs & celltimes).

--------

Lastly, kT and I talked this past weekend, and he was successful in converting the PAL movie into NTSC and didn't even have to touch the audio...apparently it muxed in just fine.

[staul62]

To answer your questions in order:

I go from 25fps to 23.976 for movies only because movies encoded in PAL are sped up by 4% to present films shot at 24fps in the 25fps required by PAL video. I hate the speedup and I can tell the difference.

To add the appropriate pulldown flags to my 23.976fps video, I use pulldown.exe - a command line program.

If converting your video via Avisynth, assumefps(23.976) is the appropriate function to use. I don't do this - I simply patch the header to say that it's 23.976 and don't otherwise touch the video. This works for me for PC playback and again I can point you to the post listing my procedure if you wish.

For interlaced video I would assume a video (not film) source and no speed change would be required. Your (kT's) approach would be fine. It's simply a 25fps to 29.97fps pulldown with no speed change and therefore no audio length change.

As for Avisynth scripts - they're out there. A search of this forum or a general search should turn up at least a few.

Hope this helps. Corrections and alternate options welcome!

Steve