Splitting MP4 results in out-of-sync file but only when it's a small split

[poseyj]

Hey there. I'm trying to run this on an mp4 that is 01:35:00 long.

ffmpeg -i test.mp4 -vcodec copy -acodec copy -async 1 -ss 01:30:00 -to 01:35:00 output.mp4

And I'm getting an out of sync file by about 1 second. What I find weird is, let's say I select 00:00:00 to 1:30:00, that big file it spits out is in sync, all great. I select first 20 minutes, sync is great. last 20 minutes, sync is off. Last 5 minutes, sync is off. Source file is in sync throughout.

This happens consistently and it's either in sync perfectly or off by a second or so. Sync does not get progressively worse. Any help would be appreciated

File infoI know 512kbps audio is ridiculous, I didn't create this file I'm only trying to split it!)

General
Complete name : C:\Users\CountRushmore\Downloads\ffmpeg\ffmpeg-20150907-git-b480f0e-win64-static\bin\3755.mp4
Format : MPEG-4
Format profile : Base Media / Version 2
Codec ID : mp42
File size : 1.33 GiB
Duration : 1h 16mn
Overall bit rate mode : Variable
Overall bit rate : 2 478 Kbps
Encoded date : UTC 2015-09-07 00:56:27
Tagged date : UTC 2015-09-07 00:56:27

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Main@L3.1
Format settings, CABAC : Yes
Format settings, ReFrames : 2 frames
Format settings, GOP : M=1, N=60
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 1h 16mn
Source duration : 1h 16mn
Bit rate mode : Constant
Bit rate : 1 962 Kbps
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Variable
Frame rate : 29.970 fps
Minimum frame rate : 29.970 fps
Maximum frame rate : 30.000 fps
Standard : NTSC
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.071
Stream size : 1.05 GiB (79%)
Source stream size : 1.05 GiB (79%)
Language : English
Encoded date : UTC 2015-09-07 00:56:27
Tagged date : UTC 2015-09-07 00:56:27
Color range : Limited
mdhd_Duration : 4612000

Audio
ID : 2
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 1h 16mn
Source duration : 1h 16mn
Bit rate mode : Variable
Bit rate : 512 Kbps
Maximum bit rate : 564 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 KHz
Compression mode : Lossy
Stream size : 282 MiB (21%)
Source stream size : 282 MiB (21%)
Language : English
Encoded date : UTC 2015-09-07 00:56:27
Tagged date : UTC 2015-09-07 00:56:27
mdhd_Duration : 4612111

[Baldrick]

What does -async do?

Or try split with mp4box and see if it works better. See https://gpac.wp.mines-telecom.fr/mp4box/mp4box-documentation/ and under Splitting. Install the gpac package and you will get mp4box.exe in some folder.

[poseyj]

MP4Box works like a charm, thanks! I wasn't sure what async did. I had googled it and some people had it in their strings.