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I am trying to concatenate two videos using FFMPEG concat. The second video plays a slower speed and loses it's audio, but not only that, the time elapsed counter in the windows video player also slows down. When I play it in VLC, the timing is fine but the audio is still missing. I have searched many articles but can not find an answer. I'd prefer not to re-encode the videos. I am trying to make a tiktok compilation so I download the tiktoks and then use ffmpeg to create it. I am using win 10 and running it in cmd. Thank you for your help in advance and let me know if I can clarify anything here.

To explain this effect better please view the video. Notice how the timer counts slowly https://youtube.com/shorts/k6QD_oqTRyE?feature=share

What I have done is used the ffprobe to compare the details of the videos since they are both 30 fps, mp4 files, same size, and tbn.

Video 1 Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, smpte170m/bt470bg/smpte170m, progressive), 1024x576 [SAR 1:1 DAR 16:9], 622 kb/s, 30 fps, 30 tbr, 15360 tbn (default)

Video 2 Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1024x576 [SAR 1:1 DAR 16:9], 760 kb/s, 30 fps, 30 tbr, 15360 tbn (default)

Output video Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1024x576 [SAR 1:1 DAR 16:9], 655 kb/s, 29.92 fps, 30 tbr, 15360 tbn (default)

This is my code for concat

ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mp4

And this is the code during the concat process

libavutil 57. 24.101 / 57. 24.101 libavcodec 59. 25.100 / 59. 25.100 libavformat 59. 20.101 / 59. 20.101 libavdevice 59. 6.100 / 59. 6.100 libavfilter 8. 29.100 / 8. 29.100 libswscale 6. 6.100 / 6. 6.100 libswresample 4. 6.100 / 4. 6.100 libpostproc 56. 5.100 / 56. 5.100 [mov,mp4,m4a,3gp,3g2,mj2 @ 000002a98ca76880] Auto-inserting h264_mp4toannexb bitstream filter Input #0, concat, from 'mylist.txt': Duration: N/A, start: 0.000000, bitrate: 792 kb/s Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1024x576 [SAR 1:1 DAR 16:9], 760 kb/s, 30 fps, 30 tbr, 15360 tbn Metadata: handler_name : VideoHandler vendor_id : [0][0][0][0] Stream #0:1(und): Audio: aac (HE-AACv2) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 32 kb/s Metadata: handler_name : SoundHandler vendor_id : [0][0][0][0] Output #0, mp4, to 'output.mp4': Metadata: encoder : Lavf59.20.101 Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1024x576 [SAR 1:1 DAR 16:9], q=2-31, 760 kb/s, 30 fps, 30 tbr, 15360 tbn Metadata: handler_name : VideoHandler vendor_id : [0][0][0][0] Stream #0:1(und): Audio: aac (HE-AACv2) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 32 kb/s Metadata: handler_name : SoundHandler vendor_id : [0][0][0][0] Stream mapping: Stream #0:0 -> #0:0 (copy) Stream #0:1 -> #0:1 (copy) Press [q] to stop, [?] for help [mov,mp4,m4a,3gp,3g2,mj2 @ 000002a98ca89380] Auto-inserting h264_mp4toannexb bitstream filter frame= 1737 fps=0.0 q=-1.0 Lsize= 5442kB time=00:00:58.14 bitrate= 766.8kbits/s speed= 989x video:4647kB audio:736kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.084181%

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