Frame rate to compensate for audio delay

[SushiSky]

I have two sources of the same event, but one has a hd video stream and the other has a audio track that I want. Consequently after I spliced them together, the audio was progressively out of sync. After looking into the two sources, I realised their frame count differed. So my question is, is it possible to give both a frame rate that will allow them to have the same playing time and hence allow the audio to be synced? If so, how? Any other suggestions would be greatly appreciated

[Alex_ander]

It is only possible to apply pulldown to progressive mpeg2 video track in case you want to make it slightly longer (no re-encoding), otherwise you'd have to work with audio track in a sound editor and then re-encode it.

[jagabo]

Depending on what codecs and containers you have, you may be able to simply change the frame rate. But you'll find that different sources are different cuts of the movie (ie, added or cut scenes), not just different lengths. So that approach may not work, even if the codec and container is amenable to changing the frame rate.

[poisondeathray]

Are you still working on the same thing? It won't work for you

You have a VFR video of the original video. (It's missing frames, but not necessarily linearly or evenly distributed) . Just time compressing the audio will cause it to go in and out of sync

"Automatically" converting it to CFR (e.g. avisynth convertfps=true , or VFRtoCFR) inserts duplicates approximately where they should be - but that' s just it - approximate means it will roughly be in sync but go may go slightly out of sync in places. It might be "good enough" for you, it's certainly more simple than doing it manually

The only way to get it "perfect" is to use identical frames, eg. manually in a NLE . IIRC the "bad" video source was SD (with "good" audio). The SD source is CFR and has more frames. The upscaled frames won't look so good (you're copying from the SD source to "paste" into the HD source). But if they are exact duplicates in the CFR source, you can copy from the HD source back to the HD source (just using the SD source as a "guide" as to where they go)

[SushiSky]

If both are CFR?

[poisondeathray]

If both are CFR?

It doesn't matter.

Basically it comes down to this: You have 2 different versions. 1 has different (more) frames. If you want to switch the audio, you need the frames to match.

[SushiSky]

What is the easiest way of accomplishing this? Really appreciate all the help you given me

[poisondeathray]

What is the easiest way of accomplishing this? Really appreciate all the help you given me

I already explained. You use a video editor. Copy & paste frames from the one that has more frames into the shorter duration HD video (the one with less frames)

But if the one you're copying from is SD or low quality , the copied frames will look bad compared to the other surrounding higher quality frames

[SushiSky]

Would it be better to delete the frames instead?

[poisondeathray]

Would it be better to delete the frames instead?

It would, but it won't work in your case

The "good video" has fewer frames . You can only delete from the video that has more frames, but then the "good audio" won't match


Video 1 = good video, fewer frames, bad audio
Video 2 = bad video, more frames, good audio

[SushiSky]

Would the flickering of the frames in & out affect it very much? Can I simply multiply existing frames of the same quality as a buffer?

[poisondeathray]

Would the flickering of the frames in & out affect it very much? Can I simply multiply existing frames of the same quality as a buffer?

I have no idea what you're asking - can you clarify

[SushiSky]

For example, one scene in the bad video source has 56 frames and the other has 50 frames. Instead of copying lower quality frames, should I just copy existing frames to make the frames match? Would it be very noticeable?

[Alex_ander]

It will be noticeable in case you insert full frames on some non-multiple basis (e.g. not exactly doubling or tripling the frame rate). Less noticeable (and maybe even quite acceptable) in case you insert individual fields and re-interlace the video (pulldown).

[SushiSky]

Whats the easiest way to change frame rates on a mac

[SushiSky]

Does the audio sampling rate affect the sync?

[SushiSky]

Bump

[hello_hello]

Does the audio sampling rate affect the sync?

If you mean can you re-encode audio while changing the sample rate without it effecting the sync? Yes. As long as it's resampled correctly and the new version has the same duration as the original, that's all that matters.

[SushiSky]

Will the two sources be in sync if one has a 44.1KHz sampling rate and the other a 48KHz sampling rate?

[poisondeathray]

Will the two sources be in sync if one has a 44.1KHz sampling rate and the other a 48KHz sampling rate?

maybe , maybe not . The sampling rate alone isn't enough information

Compare the waveforms in an audio editor. If they are the same duration, same waveform, then they are the same

[hello_hello]

Yeah the sample rate as such has no effect on the audio/video sync. Assuming both audio tracks are exactly the same in every other way then they'll both sync correctly whether they be 44.1KHz or 48KHz etc.