Convert FLV 25fps to 29.97fps

[Jason77]

Hello,
I realize there have been many, many posts about this, but I still can't seem to get the right combination to work. I'm trying to convert some downloaded FLV files from 25fps to 29.97fps in order to create a DVD.

I extract the streams using FLVExtract then, using VirtualDub, convert the video stream to 29.97fps. I use Audacity to shrink the audio stream to match the time length of the video stream. The two streams are combined in VirtualDub and saved to AVI. I play this AVI file and there is a definite audio/video sync error. Sometimes they're synced at the beginning of the movie, and gradually get out of sync as time goes on. Other times the audio/video is not synced right from the start.

Any help is greatly appreciated!

[Gavino]

I extract the streams using FLVExtract then, using VirtualDub, convert the video stream to 29.97fps. I use Audacity to shrink the audio stream to match the time length of the video stream.

Changing the video frame rate should not change its duration, so there should be no need to touch the audio.

I suspect in the 'Video frame rate control' dialog, you changed the rate in the 'Source rate adjustment' section instead of the 'Frame rate conversion' part.

[jagabo]

Leave the video at 25 fps and encode as MPEG2 at 720x480 progressive. Then use DgPulldown to add pulldown flags. Author your DVD. There will be no need to change the audio.

[Jason77]

Gavino: Indeed, I changed the rate in the "source rate adjustment" section. I'm anxious to try your method.

Jagabo: I'm eager to try your method as well...it's definitely a new one I haven't read about.

Thanks for the help!!

[jagabo]

Using VirtualDub as Gavino suggested will duplicate every 5th frame to perform the frame rate conversion. Ie, 5 frames become 6, 25 frames become 30 (every now and then the duplicate will be skipped to make up for the difference between 29.97 fps and 30 fps). That will create 5 little jerks every second.

Encoding at 25 fps and using pulldown will create pulldown judder similar to most movie DVDs you watch on NTSC systems. Most people consider that less objectionable than the jerkiness of frame duplication.

A third method is to slow the frame rate down to 23.976 fps and apply the usual 3:2 pulldown flags -- like most NTSC movie DVDs. But then you also have to adjust the audio length. Since most movies are shot at 24 fps, and sped up to 25 fps for PAL systems, slowing the frame rate down will usually restore the proper running time of the video (PAL conversions usually run about 4 percent shorter).

[Gavino]

My 'solution' was offered as a simple correction to your original procedure.
Using pulldown as jagabo suggests will give a smoother result.
(The 'third method' of course only makes sense if the source was originally shot on film rather than video.)

[Calidore]

Using VirtualDub as Gavino suggested will duplicate every 5th frame to perform the frame rate conversion. Ie, 5 frames become 6, 25 frames become 30 (every now and then the duplicate will be skipped to make up for the difference between 29.97 fps and 30 fps). That will create 5 little jerks every second.

Encoding at 25 fps and using pulldown will create pulldown judder similar to most movie DVDs you watch on NTSC systems. Most people consider that less objectionable than the jerkiness of frame duplication.

A third method is to slow the frame rate down to 23.976 fps and apply the usual 3:2 pulldown flags -- like most NTSC movie DVDs. But then you also have to adjust the audio length. Since most movies are shot at 24 fps, and sped up to 25 fps for PAL systems, slowing the frame rate down will usually restore the proper running time of the video (PAL conversions usually run about 4 percent shorter).

Jagabo's third method is what I use. Instead of extracting the streams, using Audacity, and remuxing, you can save a couple of steps by simply loading the FLV into vdub and using the "stretch" advanced audio filter with a ratio of 1.04271.

Best,

Calidore