Converting 25fps to 23.976fps and new wav is same length?

[videocheez]

I'm using besweet, the new beta to convert a 25fps movie's auduio to 23.976fps and the resulting wav, after conversion is the same length as the original wav. It's about five minutes shorter than the converted avi. My ultimate goal is to convert so that I can burn to DVD. The video converted nicely but I'm confused with the audio. Any suggestion or other methods to do the framerate conversion would be appreciated.

Thanks in advance,

VC

[txpharoah]

Huh?
I hear this a lot, and it confuses me.

A framerate is so many frames per second.

As in 23.976 fps
Or 25 fps
Or 29.97 fps.

In all cases, you're speaking about ONE SECOND of time.

The audio will be one second long, no matter the framerate.

It won't become longer or shorter (unless you stretch the actual frames into a new timeslot - aka Do Not Frame Rate Conversion in TMPGenc).

The framerate conversion is only for the video. The audio conversion is to adjust the framerate flags on the audio file.

Your WAV should be the same length. Remux it with the video and see.

[videocheez]

Thanks for the reply. Like you I also thought that the duration of the audio should not change just because I converted the framerate but I did a little research yesterday before asking my question in the forum and some how figured that the audio needs to be longer, since the resulting video file is longer.

The framerate conversion is only for the video. The audio conversion is to adjust the framerate flags on the audio file.

My mpeg2 file is about 5 minutes longer than my converted audio file. Are you saying that when I did the framerate conversion of the audio, I merely adjusted the flags so that it will match up with the framerate converted video?
I'll take your suggestion and try muxing the the two converted streams. I just asked the question last night before bed to get some fresh ideas for today.

Thanks,

VC

[adam]

That is incorrect txpharoah. To convert film to NTSC new frames are created from existing fields and added every second, so even though the # of frames has increased, the number of seconds hasn't, and therefore the playtime is the same.

But with PAL, the video is physically sped up. Those same number of frames are playing in a faster speed and therefore the movie finishes earlier. If you convert a PAL audio source to NTSC than the playtime of both the audio and the video should increase by about 4%.

Take a look on amazon.com or IMDB.com and compare the R1 and R2 releases of movies. You will see that invariably the R2 versions are 4% shorter in playtime because they are in PAL as opposed to NTSC.

There are no such things as framerate tags on the audio stream. Audio streams can contain a drop frame tag, but the audio does not have a framerate, nor is the framerate of the video represented in any flag in the audio stream. Simply put, audio has a certain playtime. Depending on what type of format conversion you are doing your video may or may not change in duration as a result of a change in playback speed. You need to ensure that your audio's speed is adjusted according to your video's speed. So yes, framerate conversions definitely apply to both the video and audio whenever you bring PAL into the picture.

[txpharoah]

That still seems strange that PAL would distort the audio from speeding it up. I have never really worked with PAL, outside of some digital conversions created with a muxed MPEG2/MP2 stream using ProCoder, and some PAL tapes played on worldwide machines, captured from the NTSC output.

Oh well. Another reason to like NTSC, and another reason to leave PAL conversions to those with more time and patience.

Hey adam, what would YOU suggest as the best way to convert a PAL DVD to a NTSC DVD, without using CCE/AVIsynth? I've got a movie that is PAL, and while I can play PAL discs, this one refuses to playback as 16:9 as it is supposed to.

I need to fix that, and would like to convert to NTSC all at the same time.

Right now, I have ProCoder, TMPGenc Plus, Cleaner 5 (for audio, sucks at video) and SoundForge 6 (with MC) installed. Others too, but these are probably most important. AVIsynth and CCE are acting up after installing AVIsynthesizer and one other one (name slips me at the moment) to help write the scripts. I've got BeSweet too, but the sound is just bad on it (tin-can sound). I use SoftEncode for AC3 encode/decode.

I've got quite a few people, both online and off, asking me for the best method, and I just keep telling them what I know. It's working so far, as no complaints yet, but there's got to be a more fool-proof method. Right now, from MPEG2/MP2 source (or the PCM/AC3 converted to MP2 and muxed with the video) I use ProCoder, set to drop/add frames, not blend, and converted from 25fps to 29.97fps. It's slightly 'bumpy' on the 29.97 and really jerky on the 23.976 (so I have avoided that one).

Would you suggest converting the 25fps to 29.97 or 23.976? And do you drop/add the frames or span it out (TMPGenc's Do Not Framerate Conversion - using all 25fps, no matter how much the time gets shifted by reducing/shrinking to the new framerate)? I would think that would slow it back down again, seeing as how it is apparently 4% faster.

I'd experiment myself, but time is not widely available right now. I've had this movie for 2 months already, not yet watched it. I trust your suggestions.

[videocheez]

I learn a lot reading the threads that you two get involved with especially when you have differing views.
I was wondering however if either of you remember my original question and have any suggestion as to a good method for converting the audio framerate from 25fps to 23.976fps.

Any suggestion or other methods to do the framerate conversion would be appreciated

The Guide at the left is a little outdated and refers to older versions of besweet and cool edit.
If I can do it with CCE all the better. I already used CCE to convert the video and it looks great.
I did pulldown on the video so i am also wondering if I should try to convert the audio from 25fps to 29.97 instead of 23.976.
Any help would be appreciated.

Thanks again,

VC

[adam]

For the video you always want to convert from 25fps to 23.976fps, never to 29.97fps. The only difference between film (23.976fps) and PAL is the playback speed, the actual frames are identical. When you convert film to NTSC (29.976fps) the frames must be split into fields and the fields must be repeated in a specific pattern otherwise the playback is not smooth. So if you just convert 25fps to 29.97fps then at best fields are being repeated in no specific pattern, and at worst you are simply duplicating whole frames which causes horrible motion problems. Besides, NTSCfilm has some very major quality advantages over NTSC, and if possible you should always opt to encode to NTSCfilm instead.

So, for the video just set your encoder's output to the desired NTSC compliant resolution and set the output framerate to 23.976 and that's really all there is to it, except that you must run the video through pulldown.exe afterwards to add the pulldown flags otherwise the DVD player won't telecine the video to 29.97fps at playback and your DVD will be non-compliant. One more important thing to realize is that TMPGenc has a "feature" though I think of it more like a crutch, where by default it does not actually change speed when you convert to a new fps. Instead it randomly adds or decimates frames so as to preserve audio sync. The problem is that this creates jerky motion, and incidentally this is NEVER how any type of framerate conversion is supposed to be done. To turn this features off, enable the "do not framerate conversion" filter on the advanced tab. NEVER ADD/DROP frames when converting between regional formats. This feature should only be used on sources which do not comply with any regional format, ie: 20fps.

As for audio, you need to slow it down by exactly 4.03%. I've had nothing but good results using BeSweet to do this using its built in regional format conversion options, but if you don't want to use BeSweet there are many other options. Basically just decompress your AC3 to wav and then use a wav editor. Most wav editors have some sort of time stretching option, or you could load your audio and video streams in a NLE like Premiere and then just adjust the physical length of your audio stream to match your encoded video.

Another thing to take into consideration is the audio pitch. Whenever you change the speed of audio it changes the pitch proportionally, so when converting PAL to NTSC your pitch will be lowered by 4.03%. Depending on the nature of the source, it may or may not sound better if you offset this change by raising the pitch 4.03% after slowing down the playback speed. You'll just have to try it both ways and do a quick test to see if you get better results with the change, though usually you can just skip this step. Some sources sound absolutely horrible when you adjust the pitch, ie: slow tempo music.

Once you have the video converted and the audio properly adjusted just multiplex and burn.

[videocheez]

Thanks for the info. That cleared up a lot. I was successful stretching the audio (slowing down) by using cool edit and multiplying the maximum time by 1.043 like you suggested. Too bad the ratio is a repeating decimal. The length of the audio and the video differ by seven seconds so I noticed an itty bitty sync problem in the last 10 minutes. I can live with it but i'm going to try adjusting the multiplication factor by a small amount to see if I can nail it down.
I didn't notice the pitch problem but I did notice that the volume was lowered so I had to crank the speakers up so much that I had some background hiss. With the help of you guys these are small problems that will be fun to fool with.

Thanks again,
VC

[scottymac]

The length of the audio and the video differ by seven seconds so I noticed an itty bitty sync problem in the last 10 minutes.

To get an exact length (within tenths of a second)

Load your MPG in Virtualdub Mod, find exact length, load audio file in Cool Edit (I actually use Sound Forge) and input the exact length that you want the audio to be, and it stretches it just about exactly to the length you want.

Question for you though, how do you convert back to MP2 or Multiplex your new audio with your converted video file?

[videocheez]

Thanks for your advice. To answer your question now:

Question for you though, how do you convert back to MP2 or Multiplex your new audio with your converted video file?.

What I do with the audio is convert it to ac3 format. I then enter my mpeg with out audio and my ac3 audio into an authoring program and the authoring progam multiplexes the video and the audio automatically so long as the two files have the same name. (eg movie.mpg and movie.ac3)

Lately i've been authoring with DVDA.

Good Luck,

VC