audo audio sync lost when trying to merge two mp4

[spaceharfang]

I have two mp4 (h264,dts) that I'm trying to merge in a new mp4 (h264,ac3).
The audio looses sync on the transition between the two files, making the second half of the resulting file unsynched.

Here is the log

5m 12.13s: UILog: MsgWork:current work finish: 4
 5m 18.20s: Source manager: open source flag:1,0,1,1,1
 5m 54.24s: UILog: OnMsgToolbar_Start
 5m 54.24s: UILog: Msg Start: ready start
 5m 54.26s: UILog: Msg Start: start test run work
 5m 54.26s: UILog: Msg Start: run work
 5m 54.26s: UILog: Run current Work.
 5m 54.26s: UILog: Begin work copy or converter.
 5m 54.26s: Start check Video Converter register status.
 5m 54.26s: End check Video Converter register status: Enable
 5m 54.26s: UILog: start running at thread.
 5m 54.27s: UILog: return flag at start running at thread ok.
 5m 54.28s: OPList at BD Converter : (0.2),(1.2)
 5m 54.28s: Video Converter check watermark flag: 0
 5m 54.60s: OPList at BD Converter : (0.2),(1.2)
 5m 54.60s: Video Converter check watermark flag: 0
 5m 54.81s: OPList after translated for merge: (0.2),(1.2)
 5m 54.81s: OPList after translated for merge: (0.2),(1.2)
 5m 54.82s: ------------------  convert work begin(1/2)  ------------------ 
 5m 54.82s: start process(1/2)

------ process working ------
 0m 00.43s: info, try to open file D:/Users/public/DVDFab/The Flash (2014) - S2E08A - Legends of Today (part 1)/The Flash (2014) - S2E08A - Legends of Today (part 1)-1.m4v
 0m 00.53s: info: open successed, iformat = QuickTime / MOV
 0m 00.54s: info: create config(videoconvert)
 0m 00.54s: info: crop value after clone: left = 0 right= 0 top=0 bottom=0 enable=0 mode=0
 0m 00.54s: info: use profile(MP4)
 0m 00.54s: info: file (.m4v)
 0m 00.54s: info: 3D working_mode(disable), 3D format(sbs_lef_right) 
 0m 00.55s: info: stream input@ Video(1)[codec(h264) size(1920*1080) fps(24000/1001) interlace(0) duration(2582)sec opcode(compress)]
 0m 00.55s: info: user use trim mode: trim_start_time = 0 ,trim_end_time = 2580 
 0m 00.55s: info: perset file config OK ! 
 0m 00.55s: info: set output video frame_rate(24000/1001)
 0m 00.56s: info: recommand= 0, Shrink support= 0, enable= 0, cuda_cap= 0 , cpu_count= 8
 0m 00.56s: info: vdecode hevc= 0, h264= 0, vc1= 0, mpeg2= 0, vencode h264= 0, hevc= 0 , plat = 2 
 0m 00.56s: info: stream output Video(1)[codec(h264) size(1920*1080) fps(24000/1001) interlace(0) bitrate(20000) duration(2582)sec]
 0m 00.57s: info: stream input@ Audio(2)[codec(dca) channels(6) sample(48000) bitrate(1536000) bitdepth(16) opcode(compress)]
 0m 00.58s: info: stream output Audio(2)[codec(ac3) channels(6) sample(48000) bitrate(640000) bitdepth(16) opcode(compress)]
 0m 00.58s: info: SubMode(Render) -- Display Only forced Subtitle(false) 
 6m 00.26s: UILog:MsgWork:WorkStatus_Start
 0m 00.60s: info: enable multi-thread software decoder, thread count = 8
 0m 00.60s: info: ex process path= C:/Program Files (x86)/DVDFab 10/fabcore.exe
 0m 01.79s: info: h264_encode: encode param profile(1) level(41) bitrate(20000) crf(-1) interlace(0)
69m 10.36s: info: audio_decode finish job
69m 10.36s: audio_encode finish job
69m 23.14s: 
------ process exit ------
75m 22.81s: ------------------  convert work finished  ------------------
75m 22.81s: ------------------  convert work begin(2/2)  ------------------ 
75m 22.81s: start process(2/2)
69m 23.21s: 
------ process working ------
69m 23.21s: info, try to open file D:/Users/public/DVDFab/The Flash (2014) - S2E08B - Legends of Yesterday (part 2)/The Flash (2014) - S2E08B - Legends of Yesterday (part 2)-1.m4v
69m 23.53s: info: open successed, iformat = QuickTime / MOV
69m 23.55s: info: create config(videoconvert)
69m 23.55s: info: crop value after clone: left = 0 right= 0 top=0 bottom=0 enable=0 mode=0
69m 23.55s: info: use profile(MP4)
69m 23.55s: info: file (.m4v)
69m 23.55s: info: 3D working_mode(disable), 3D format(sbs_lef_right) 
69m 23.56s: info: stream input@ Video(1)[codec(h264) size(1920*1080) fps(24000/1001) interlace(0) duration(2626)sec opcode(compress)]
69m 23.56s: info: perset file config OK ! 
69m 23.57s: info: set output video frame_rate(24000/1001)
69m 23.57s: info: vdecode hevc= 0, h264= 0, vc1= 0, mpeg2= 0, vencode h264= 0, hevc= 0 , plat = 2 
69m 23.57s: info: stream output Video(1)[codec(h264) size(1920*1080) fps(24000/1001) interlace(0) bitrate(20000) duration(2626)sec]
69m 23.57s: info: stream input@ Audio(2)[codec(dca) channels(6) sample(48000) bitrate(1536000) bitdepth(16) opcode(compress)]
69m 23.58s: info: stream output Audio(2)[codec(ac3) channels(6) sample(48000) bitrate(640000) bitdepth(16) opcode(compress)]
69m 23.58s: info: SubMode(Render) -- Display Only forced Subtitle(false) 
75m 23.26s: UILog:MsgWork:WorkStatus_Start
69m 23.60s: info: enable multi-thread software decoder, thread count = 8
69m 23.60s: info: ex process path= C:/Program Files (x86)/DVDFab 10/fabcore.exe
69m 25.03s: info: h264_encode: encode param profile(1) level(41) bitrate(20000) crf(-1) interlace(0)
142m 54.92s: info: audio_decode finish job
142m 54.92s: audio_encode finish job
143m 07.93s: 
------ process exit ------
149m 08.10s: ------------------  convert work finished  ------------------
149m 09.12s: UILog: MsgWork:current work finish: 3
149m 09.13s: UILog: Run Work to end.
149m 19.64s: Source manager: open source flag:1,0,1,1,1
163m 11.43s: Exit process: stop running.
163m 14.62s: Exit process: preview pfn_releaseplayer end
163m 14.62s: Exit process: preview pfn_deinit end
163m 14.64s: Exit process: preview FreeLibrary end
163m 14.75s: Exit process: finish MainUI.
163m 14.75s: Exit process: finish FreePref.
163m 14.76s: Exit process: finish AVEditWrap Release.
 0m 00.04s:

[spaceharfang]

I managed to get it working on Adobe Premiere Pro (such a steep learning curve, ouch!)

As a matter of fact the first file had an audio stream that was actually shorter than its video stream.

So to avoid that issue, maybe a hard sync should be added at the beginning of every file in a merge task. Just to make sure each new file starts synced.