Audio running faster? + How do I determine video & audio fps?

[alex17563]

Hello!

I've encountered a problem and haven't been able to find a solution so I hope someone here can help me..!

Well, I have 2 movie files. One has very good picture quility (BDRip, .mkv) and the other one has the desirable audio track (.avi, different language). I have found a way to extract the audio from the .avi (in both .ac3 and .mp3 formats). Using mkvmerge GUI I have merged the two of them, after applying a delay to the audio track to match the start of the movie.

The problem is that even though it starts out in sync, the audio is "running faster" than the video and the gap grows constantly larger!

Any ideas??!

Although I don't know if the term "fps" can be used for audio, what I thought was that maybe it had something to do with a difference in the audio and video's fps.. I don't know how to determine the audio's fps at all and I sometimes have difficulties determining the video's fps as well. Could it have something to do with this??

If you need more information, just ask and... Thank you in advance~!

[manono]

Any ideas??!

Perhaps the video is from an NTSC source and the audio is from a PAL source.

Audio doesn't have a framerate

If you need more information, just ask

How long is the movie and how long is the audio you added to the movie? What's the framerate of the movie? If you don't know open it in MediaInfo to find out.

[jagabo]

Mkvmerge has an audio delay parameter that you can use to set when the audio starts relative to the video. There's also a stretch feature which you can use to make the audio play faster or slower. But many players will not respond to that option. You could change the frame rate of the video to make it play faster or slower. But that may not be practical. Most audio editors have the ability to stretch or squish the audio playing time. Audacity has the ability and is free.

[alex17563]

Thanks for the MediaInfo!! I was sooooo looking for something like this~!

Well, the .mkv's fps is 23.796 (the .avi's is 25.000).
The duration is 1.27.29 for the .mkv and 1.31.44 for the .avi (hours.minutes.seconds)

By the way, is there a player that displays milliseconds?

I have Audacity but haven't figured out how to use it... There's a lot of options I don't understand and they kinda confuse me..
I try to ignore those I don't understand and search to see what I can do, but I haven't found how to stretch the audio yet. Only how to apply a delay at the start of the track..

Also, the stretch in mkvmerge is to be applied as a fraction so I don't really get how I can stretch it that way..

[jagabo]

Thanks for the MediaInfo!! I was sooooo looking for something like this~!

Be careful. MediaInfo is very useful but it's sometimes wrong.

Well, the .mkv's fps is 23.796 (the .avi's is 25.000).
The duration is 1.27.29 for the .mkv and 1.31.44 for the .avi (hours.minutes.seconds)

The MKV is from an NTSC source, the AVI is from a PAL source. Movies are usually slowed from 24 fps to 23.976 fps for NTSC release, and sped up to 25 FPS for PAL release. That means the PAL version has a 4.096 percent shorter running time. But your two videos differ by more than that so there is something else different. It may be as simple as someone cutting off a studio log at the start or end, or you may have different cuts of the movie (it's very common for scenes to be added or removed in different countries). So even if you adjust the audio to match the video at the start and end you may end up with differences in the middle. The only solution to that problem would be to use a real editor that lets you cut/insert audio in addition to adjusting the length.

I have Audacity but haven't figured out how to use it...

First, get the ffmpeg source plugin for Audacity. With that you can import the audio directly from the video file. After importing the audio use the Change Pitch, Speed, or Tempo tools on the Effect menu.

Also, the stretch in mkvmerge is to be applied as a fraction so I don't really get how I can stretch it that way..

You can either use a floating point number or a fraction. Just as an example, your MKV source is 1:27:29, or 5249 seconds long. Your AVI source is 1:31:44, or 5504 seconds long. I don't remember which video and audio tracks you want to keep but the fraction to use is either 5249/5504 or 5504/5249. Or you can perform the division and enter those as decimal values (0.95367, or 1.04858)

But that's not going to work for you because there's something more than just a run time difference between the two videos.

[manono]

Well, the .mkv's fps is 23.796 (the .avi's is 25.000).
The duration is 1.27.29 for the .mkv and 1.31.44 for the .avi (hours.minutes.seconds)

Are you sure about those numbers? The PAL video (the AVI) should be nearly 4 minutes shorter than the NTSC one, not longer as you're saying. Are you sure you didn't reverse something somewhere?

How much of a delay did you use to synch up the beginning of the audio with the video before you discovered they got more and more out of synch? Something on the order of 40 seconds?

[alex17563]

@manono

Wow.. You're right! I did reverse them.. Sorry!!!

Well, even less of a delay. About 33.5 seconds.. After that they started in sync allright.. Until chaos that is.


@jagabo

I don't know.. I haven't noticed any difference in scenes.. I don't think there's anything extra in either one of them.. But if that's what the problem is then there's not really anithing I can do, right?

I try working with audacity right now but my computer is kinda slow with this program..

[jagabo]

Well, even less of a delay. About 33.5 seconds.. After that they started in sync allright.. I haven't noticed any difference in scenes..

33.5 seconds is about the difference between the the expected PAL and NTSC run times. When you mux the audio and video try specifying the 33.5 second delay for the audio and changing the video frame rate from 23.976 to 25, or vice versa. In sync now? Actually, after changing the frame rate you may have to readjust the delay.

[alex17563]

Sorry for the delay!

I tried many things in the meanwhile but they didn't really work. I've given up trying to edit my videos. It takes a both lot of time and, more importantly, my laptop overheats so much that I have to cool it down with the hair dryer's cool air mode!!

As for that particular movie I didn't manage anything at all, but I'm starting to think that there's something wrong with the video or the audio itself.. I'll try again with different versions of both the audio and video.

The reason that I think that is because I managed to complete this task with a lot more movies by editing the audio..


This is the way I made it work for me:

1) PAL slowdown (for audio) from 25 to 24 (=23.976) with eac3to *
2) unite video-audio + apply delay of video/audio depending on the files with mkvmerge


* you'll need this GUI. Download it from Mediafire as the first post instructs and then follow steps 1-3 of post #2 of: https://forum.videohelp.com/threads/300964-Help-Split-6-Channels-into-separate-WAVs {it doesn't have to be a 6-channel AC3 track, it can be any .ac3/.mp3 file} and then follow all the instructions of post #16 of: https://forum.videohelp.com/threads/312812-25fps-source-Ac3-to-23-976fps


extra initial steps if audio is from an .flv video file:
~ .flv audio extract with FLV Extract
~ .aac to .mp3 with http://www.aactomp3converter.com/

extra initial steps if audio is from an .avi file:
~ file ->load .avi => streams -> streams list -> select stream to extract -> demux with VirtualDubMod
OR use AviDemux: load video and then go to Audio -> Save audio (be careful! You must know the audio type from before and input it yourself at the end of the audio file's name)


Well, I tried to make this a mini guide for anyone who happens to come across the same kinds of files I have come across!

Thank you all and I'll tell you if I succeed in that one as well.. Still haven't..


{Another tool:
.mp3 to .ac3 with ffmpeggui: it's not necessary anymore as I found out that eac3to can have as input an .mp3 file and convert it into .ac3 by itself..}