Question / Help VBR vs CBR when preventing sync issues

J

Jg3555

New Member
Hi. So recently I encountered the well documented issue of audio sync problems with MP4s. I found that the audio was fine at the beginning of my recording and then starting to slip later on, but at times it would appear to catch up again and then drop again. The recording was 8mins long. I've used the same settings with shorter recordings and there have been less perceivable sync issues, in most cases it appears there are no sync issues. I couldn’t salvage the 8 min MP4 unfortunately. I tried most things - converting to ProRes, handbrake etc— it did nothing. It seems the fault was not in the codec or container but rather embedded in the original recording, presumably due to my OBS settings. In the end I managed to salvage sections of the recording by manually nudging the audio to fit with the video in Premiere. I JUST got away with it, but it took ages and wasn’t ideal.

So my question is, how can I prevent this in the future?
• Would recording as MKV (instead of mp4) and then remixing be my best bet? I have got comfortable using h264 MP4s in the past as go to solutions with other work, when rendering from After effects to create smaller file sizes than ProRes/Animation etc, but perhaps that’s not the best way to record on the fly like this?
• I was using CBR rather than VBR too. Is this wise? What are the reasons for using VBR over CBR? Is VBR more used when streaming rather than recording?
• Could my bitrate be responsible?
• Would it help to add keyframes?

My record settings:

.mp4, X264, CBR, bitrate= 50000, keyframe=0, CPU=veryfast, Audio bitrate=192

Could any of this lead to the results I've been getting?
Thanks in advance guys.
 
Harold

Harold

Active Member
Saving directly to mp4 is never recommended.

Use CRF or CQP (depending on your encoder) as your bitrate control when recording, not CBR or VBR.
CRF or CQP value of 14-23.
 
J

Jg3555

New Member
What are CRF AND CQP? Apologies, I don’t know have experience using them- what’s the difference between those and CBR or VBR? Is it best to record MKV?
 
Harold

Harold

Active Member
CRF: Constant Rate Factor
CQP: Constant Quantization Parameter

They're quality based bitrate selections.
For multitrack audio, save to mkv. For single track audio, save to either flv or mkv.
 
C

crumble1984

New Member
change to audio only and pick the capture card audio for example elgato audio #1 and the audio will be spot on, but you can't hear it in the preview.
 
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