Dummy question: How does change of frame rate effect audio?
- Thread starter lowep
- Start date
That is very good to know! I usually record in 4K30p then downsize to 1080p30 but consider filming in 60fps (only possible on my camera in 1080p) to have the possibility of stretching that out in post to look like slowmo, but until your reassuring answer was not sure if that would screw up the audio, so thanks for your reply. Now what I am not sure about is if I do film at 60fps and every other video frame is lost when I drop it into a 30fps timeline, then what't the point? Doesn't that turn my fat 60fps clip into a regular skinny 30fps clip? Looks like I need to do some more homework!
Your audio mostly doesn’t care about the frame rate of your video. Audio is dependent on sample rate, typically 48kHz in video. Even when an audio recorder uses time code, it’s not recording TC at all but is just adding a tag in the file header metadata that specifies the time base, i.e. frame rate.
If you are working with embedded audio - the sound that was recorded in-camera with the picture - it’ll follow without issue because it’s still playing at 48kHz.
Where the time base tags can get tricky is with an independent audio file, or sound recorded on a second system (separate audio recorder). If the audio recorder is using time code and is tagged with a frame rate that is different from that of the video, there will be drift when the two are dropped into a timeline together. So if your video is recorded at 23.976 and your audio file’s metadata tag is 29.97, you’ll have issues. But 60P and 30P play nice together anyway, and most sound recorders top out at a time code rate of 29.97.
If you are working with embedded audio - the sound that was recorded in-camera with the picture - it’ll follow without issue because it’s still playing at 48kHz.
Where the time base tags can get tricky is with an independent audio file, or sound recorded on a second system (separate audio recorder). If the audio recorder is using time code and is tagged with a frame rate that is different from that of the video, there will be drift when the two are dropped into a timeline together. So if your video is recorded at 23.976 and your audio file’s metadata tag is 29.97, you’ll have issues. But 60P and 30P play nice together anyway, and most sound recorders top out at a time code rate of 29.97.
Run&Gun
Veteran
Yes, when shooting at 60(59.94) real time, TC is still running at 30(29.97), at least on all of my cameras(VariCam's, C300, F55). And some cameras still run TC at 29.97 even when shooting 23.98. And some you can choose the TC rate(either 23.98 or 29.97) when you're shooting 23.98.
Noiz2
Sound Ninja
TC and audio, in the digital world, are only a positional reference and not a timebase reference.
The OP's question is not as simple as it should be.
As a rule embedded audio will follow frame rate, so slowed down footage will have slowed down audio. Now if the app you are using just drops frames (or similar) to change the frame rate and your picture speed doesn't change then the embedded audio should also follow.
Non embedded audio should not pay much attention to what is happening with video and so should stay the way it was.
The big * (asterisk) in all of this is that the programers that write the code do not always think the same way and what I said above should mostly be true it's probably not 100%. Apple famously decided to deal with drop frame differently than Everyone else (and not mention it) and that caused a bunch of issues, so you never really know till you try.
Which BTW is the unsaid part of the OP's question.
TEST your workflow before you shoot! Do 30 sec. of test whatever. Send it through your post workflow and see what happens. I can say that anyone, reputable, in sound post should not charge you extra for that kind of test. I ask for them. Hardly anyone obliges, but... It will save you stress later and post will be more than happy to get a short flow test because it means they don't have to worry so much later when time is an issue.
The OP's question is not as simple as it should be.
As a rule embedded audio will follow frame rate, so slowed down footage will have slowed down audio. Now if the app you are using just drops frames (or similar) to change the frame rate and your picture speed doesn't change then the embedded audio should also follow.
Non embedded audio should not pay much attention to what is happening with video and so should stay the way it was.
The big * (asterisk) in all of this is that the programers that write the code do not always think the same way and what I said above should mostly be true it's probably not 100%. Apple famously decided to deal with drop frame differently than Everyone else (and not mention it) and that caused a bunch of issues, so you never really know till you try.
Which BTW is the unsaid part of the OP's question.
TEST your workflow before you shoot! Do 30 sec. of test whatever. Send it through your post workflow and see what happens. I can say that anyone, reputable, in sound post should not charge you extra for that kind of test. I ask for them. Hardly anyone obliges, but... It will save you stress later and post will be more than happy to get a short flow test because it means they don't have to worry so much later when time is an issue.