25fps-source Ac3 to 23.976fps gets laggy

[kisist1]

Hello all! I hope you will find my question here

I used to sync PAL (25 FPS) audio to NTSC (23.976 FPS) video with MKV Toolnix, by set the stretching to 25/23.976.
Lately I recognized, it makes the video playback choppy and laggy. (some players make the audio choppy)

What should I to to fix this? Do I have to reencode the PAL audio?

Here is a sample:
https://docs.google.com/uc?authuser=0&id=0B3QeLWRixE4veUpNWllVVzdsbHM&export=download

[johns0]

I moved your post to a new thread where it's easier for others to help you.

[Cornucopia]

@kisist1,
The use of mmg's "stretch" function is, according to their own wiki, NOT a form of time-compression/expansion where the audio stream is re-encoded. No, it is similar to a runtime/playback version of adjusting the samplerate - EXCEPT, it does this by adjusting the timecodes. This is a novel but non-standard method; probably the reason why it is choppy.

Again (repeating from the other thread), the proper way to do this (without affecting video) is through audio time-compression/expansion (with accompanying re-encoding for compressed files).

Scott

[hello_hello]

You live in a PAL country. Rather than stretch the audio, why not use MKVToolNix to change the video frame rate from 23.976fps to 25fps instead? It should play smoothly that way.

If that's not an option you'll need to re-encode the audio. There's probably quite a few programs which will do speedup and slowdown while re-encoding. The only one I can suggest is MeGUI as it's what I'd use. It's audio encoder configuration looks like this:



For PAL to NTSC I generally do it without pitch correction as there's usually no way to know if the audio was pitch corrected when it was sped up in the first place (unless you have an NTSC version to compare it to). I think generally it isn't, but as I said, it's hard to know.

[kisist1]

Thanks to all of you!

I would like to create a dual audio MKV file, and I wanted to leave the audio untouched, but it seems not working well.

I used eac3to to do this with this command: eac3to hun.ac3 hun_slow448.ac3 -448 -slowdown
I will try MeGUI too, to compare the quality of the output audio. But I think they will provide the same quality

Thanks again!

[hello_hello]

If you do try MeGUI, for future reference, it can convert with eac3to also, depending on the video container.
As well as using MeGUI's audio conversion section you can open an MKV with the HD Streams Extractor under the Tools menu. In your case you'd check just the audio stream, choose the desired output format, and put -slowdown in the options area. When you add the job to the queue and run it, the audio will be extracted and converted with eac3to. Or there's a standalone version of the HD Streams Extractor here.

Edit: MeGUI's audio encoder uses Avisynth for the encoding, and thinking about it, if this is still accurate, eac3to is probably the better option for time-stretching multichannel audio.

http://avisynth.nl/index.php/TimeStretch
Currently the SoundTouch library only supports 1 and 2 channels. When used with more than 2 channels, each channel is processed individually in 1 channel mode. This will destroy the phase relationship between the channels.