|Feb 27, 2011, 08:27 AM||#1|
HandBrake - Audio Sync Issues
HandBrake version: 0.9.5
Preset: Apple TV (original)
Source: 720p MKV file
I found that when using "same as source" for the frame rate, audio and video went out of sync slightly, and depending on the duration of the video, it can end up being almost half a second out.
I wasn't sure if it was because the frame rate was actually 30, and the HandBrake preset was changing it to 24 so the 720p file would play back on my Apple TV. But, the preset changes the resolution to be lower (960 height instead of 1280) so the original Apple TV can play the video back at the full 30 fps.
Turns out my source is 24 fps, not 30 fps. Not that that made a difference to the output file from the Apple TV preset, because it was 24 fps (well, 23.98 to be precise). I half thought the audio sync issue might have been because HandBrake was changing the resolution to 960x544 and the frame rate to 30. But it wasn't.
I ended up just manually setting the frame rate to 24fps (23.976), and the audio is perfectly in sync now, though this is for a 20 minute video. The source 23.98, and HandBrake doesn't give me an option to set it to 23.98, just 23.976.
I'm just curious if the frame rate difference (while only very minor) would result in the audio being out of sync by a tiny fraction, but gradually getting worse and more noticeable over content that was say 3 hours?
Also, is there disadvantages to using HandBrake's 'same as source' setting?
15" MacBook Pro 2GHz i7 4GB 750GB | Mac mini 2.3GHz i7 16GB 1TB Fusion | OS X 10.8.3
iPhone 5 64GB | Apple TV 3 1080p | iOS 6.1.4
|Dec 15, 2012, 11:32 AM||#3|
23.98 is not a standard frame rate. The frame rate inside the file is most likely 23.976. It's likely that whatever program is showing you the metadata is just rounding it off.
Standard NTSC broadcast framerates are: 23.976, 29.97, and 59.94. We refer to them as 24p, 30p, and 60p just because it's easier to round it off than saying the exact numbers. There are true 24p, 48p, 30p, and 60p framerates, but those are mainly for computer formats or cinema and never used for NTSC broadcast. Since handbrake primarily converts content to NTSC standards (required by the file format), it uses the exact term of 23.976.
In summary, it's nothing to worry about and likely is not an issue.
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