Wrong framerate during FFMPEG concatenation

[qo4on]

I'm concatenating 2 video files 00000 and 00001:

ffmpeg -y -f concat -safe 0 -i file_list.txt -loglevel error -c copy test.mp4

file_list.txt:
file '00000.mp4'
file '00001.mp4'

00000.mp4:
Duration: 00:00:00.42, start: 0.000000, bitrate: 204 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 182 kb/s,
60 fps, 60 tbr, 15360 tbn, 120 tbc (default)

00001.mp4:
Duration: 00:00:01.63, start: 0.000000, bitrate: 58 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 48 kb/s,
60 fps, 60 tbr, 15360 tbn, 120 tbc (default)
The result has a different framerate:

test.mp4:
Duration: 00:00:02.05, start: 0.000000, bitrate: 85 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 76 kb/s,
59.99 fps, 60 tbr, 15360 tbn, 120 tbc (default)

How can I keep the framerate of the files constant?
I checked for a VFR:

ffmpeg -i 00000.mp4 -vf vfrdet -an -f null -
VFR:0.000000 (0/24)

ffmpeg -i 00001.mp4 -vf vfrdet -an -f null -
VFR:0.000000 (0/97)

ffmpeg -i test.mp4 -vf vfrdet -an -f null -
VFR:0.016393 (2/120) min: 256 max: 261 avg: 258

Is it possible to get VFR:0 after the concatenation?

[ProWo]

00000.mp4:
Stream #0:0(und): Video: h264 182 kb/s,

00001.mp4:
Stream #0:0(und): Video: h264 48 kb/s,

The streams have to be identical. also, you seem to have two full movies (video & audio) concatenated.
First try to concatenate the two video streams only.
If this works (identical framerate) then do the same with the audio streams. Finally mux both together.

[poisondeathray]

00000.mp4:
Stream #0:0(und): Video: h264 182 kb/s,

00001.mp4:
Stream #0:0(und): Video: h264 48 kb/s,

The streams have to be identical. also, you seem to have two full movies (video & audio) concatenated.
First try to concatenate the two video streams only.
If this works (identical framerate) then do the same with the audio streams. Finally mux both together.

The bitrate does not matter.

There is no audio in his example




@qo4on - the timestamps in the output file in the 2nd section have problems with rounding errors and jitter for some reason, even though both input files do not

Not sure if there is a magic switch in ffmpeg to do this;

Some options - you can fix the timecodes afterwards using mp4fpsmod, or use another method to join such as mp4box

eg mp4fpsmod using "inplace" editing mode (inplace mode overwrites the timecodes in the file, but you can use copy mode using -o to specify another output file instead to be safe)

"mp4fpsmod" --fps 0:60 "test.mp4" --inplace

[ProWo]

There is no audio in his example

00000.mp4:
Duration: 00:00:00.42, start: 0.000000, bitrate: 204 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 182 kb/s

00001.mp4:
Duration: 00:00:01.63, start: 0.000000, bitrate: 58 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 48 kb/s

[poisondeathray]

There is no audio in his example

00000.mp4:
Duration: 00:00:00.42, start: 0.000000, bitrate: 204 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 182 kb/s

00001.mp4:
Duration: 00:00:01.63, start: 0.000000, bitrate: 58 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080, 48 kb/s

That's a video stream 0:0 .

There is no audio stream, otherwise the ffmpeg stream list would say 0:1 or other tracks.

He posted the videos, you can download them if you want to check

The bitrate difference is from MP4 container overhead, it's an estimated value

[qo4on]

Thank you for your help!

If I overwrite the timecodes with this command:

"mp4fpsmod" --fps 0:60 "test.mp4" --inplace

Will I get out of sync audio when my input files have audio streams? I need to get exactly the same synchronization as my input files have.

[Selur]

first remuxing to transport streams and then appending the files might work,...
something along the lines of

ffmpeg -i input1.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts
ffmpeg -i input2.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate2.ts
ffmpeg -i "concat:intermediate1.ts|intermediate2.ts" -c copy -bsf:a aac_adtstoasc output.mp4

(bsf depend on the used audio&video)

Cu Selur

[ProWo]

He posted the videos, you can download them if you want to check

You are right, my mistake, sorry.

[ProWo]

Is it possible to get VFR:0 after the concatenation?

Try with My MP4Box GUI. Resulted in VFR:0.000000 (0/122) for me.

[qo4on]

Try with My MP4Box GUI. Resulted in VFR:0.000000 (0/122) for me.

I need a command line tool without a GUI. The problem is that I have several thousands of files to concatenate and I don't know how to feed them all to MP4Box. Can MP4Box take a list of video files in txt file?

[ProWo]

Read https://www.mankier.com/1/mp4box, -cat option

[qo4on]

Read https://www.mankier.com/1/mp4box, -cat option

Up to 20 cumulated -cat operations can be used.

I need a lot more than 20.

[poisondeathray]

Thank you for your help!

If I overwrite the timecodes with this command:

"mp4fpsmod" --fps 0:60 "test.mp4" --inplace

Will I get out of sync audio when my input files have audio streams? I need to get exactly the same synchronization as my input files have.

If your original files were 60.0FPS CFR (Not 59.94, otherwise you change it to --fps 0:60000/1001) , and audio, and video were exact (not one stream slightly longer, such as video 1 frame longer, or audio gaps, then it should work.

This just fixes the jitter in the timecodes that ffmpeg produced. If one or more source files had problems, and ffmpeg relied on those VFR timecodes to keep things in sync, then changing it to CFR can cause it to go slightly in and out of sync in sections

[qo4on]

@poisondeathray Can I install mp4fpsmod on Windows? I didn't find an installer.

[poisondeathray]

@poisondeathray Can I install mp4fpsmod on Windows? I didn't find an installer.

No "installer" ;

It's a "portable" exe like ffmpeg static complied windows binaries

There is a compiled binary here
https://sites.google.com/site/qaacpage/cabinet

Unzip it

[qo4on]

@poisondeathray thank you very much!

I found a few problems here:
1. tbn has changed from 15360 to 6k.
2. I tested it with hevc mp4 files with audio. I extracted wav from both files before and after and opened them in Audition. Before 7.291 sec, after 7.337 sec. The audio was shifted to the end and silence was added to the beginning. I opened both before and after hevc mp4 files in Premiere Pro and see this silence at the beginning also. ffprobe shows Duration: 00:00:07.32 for both files.

ffmpeg -i before.mp4 -vf vfrdet -an -f null -
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'before.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf58.42.100
  Duration: 00:00:07.32, start: 0.000000, bitrate: 4293 kb/s
    Stream #0:0(und): Video: hevc (Rext) (hev1 / 0x31766568), yuv420p(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 4237 kb/s, 59.93 fps, 59.94 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 22050 Hz, mono, fltp, 120 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Stream mapping:
  Stream #0:0 -> #0:0 (hevc (native) -> wrapped_avframe (native))
Press [q] to stop, [?] for help
Output #0, null, to 'pipe:':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf58.42.100
    Stream #0:0(und): Video: wrapped_avframe, yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 59.94 fps, 59.94 tbn, 59.94 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc58.80.100 wrapped_avframe
frame=  431 fps=0.0 q=-0.0 Lsize=N/A time=00:00:07.19 bitrate=N/A speed=10.3x
video:226kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[Parsed_vfrdet_0 @ 000001ddc245ee80] VFR:0.079070 (34/396) min: 256 max: 267 avg: 259

ffmpeg -i after.mp4 -vf vfrdet -an -f null -
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'after.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf58.42.100
  Duration: 00:00:07.32, start: 0.000000, bitrate: 4293 kb/s
    Stream #0:0(und): Video: hevc (Rext) (hev1 / 0x31766568), yuv420p(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 4242 kb/s, 60 fps, 60 tbr, 6k tbn, 60 tbc (default)
    Metadata:
      creation_time   : 2020-04-26T18:21:58.000000Z
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 22050 Hz, mono, fltp, 120 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Stream mapping:
  Stream #0:0 -> #0:0 (hevc (native) -> wrapped_avframe (native))
Press [q] to stop, [?] for help
Output #0, null, to 'pipe:':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf58.42.100
    Stream #0:0(und): Video: wrapped_avframe, yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 60 fps, 60 tbn, 60 tbc (default)
    Metadata:
      creation_time   : 2020-04-26T18:21:58.000000Z
      handler_name    : VideoHandler
      encoder         : Lavc58.80.100 wrapped_avframe
frame=  431 fps=0.0 q=-0.0 Lsize=N/A time=00:00:07.18 bitrate=N/A speed=10.4x
video:226kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[Parsed_vfrdet_0 @ 000001cf2becd600] VFR:0.000000 (0/430)

So, the audio turned out to be out of sync.

[poisondeathray]

What was the original before "before.mp4" ? 2 or more joined files ?

Examine the timecodes (aka. timestamps) of the before and after

If the VFR is required for sync, then you need to keep it VFR . Or reencode it to CFR (inserting frames) ,stream copy will not work in that case

[qo4on]

"before.mp4" was 23 CFR clips concatenated with ffmpeg and then audio was added after the concatenation. ffprobe for each clip:

Duration: 00:00:00.12, start: 0.000000, bitrate: 5429 kb/s
Stream #0:0(und): Video: hevc (Rext) (hev1 / 0x31766568), yuv420p(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 5381 kb/s,
60 fps, 60 tbr, 15360 tbn, 60 tbc (default)

ffmpeg -i 00000.mp4 -vf vfrdet -an -f null -
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '00000.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf58.42.100
  Duration: 00:00:00.12, start: 0.000000, bitrate: 5429 kb/s
    Stream #0:0(und): Video: hevc (Rext) (hev1 / 0x31766568), yuv420p(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 5381 kb/s, 60 fps, 60 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandler
Stream mapping:
  Stream #0:0 -> #0:0 (hevc (native) -> wrapped_avframe (native))
Press [q] to stop, [?] for help
Output #0, null, to 'pipe:':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf58.42.100
    Stream #0:0(und): Video: wrapped_avframe, yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 60 fps, 60 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc58.80.100 wrapped_avframe
frame=    7 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.11 bitrate=N/A speed=2.49x
video:4kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[Parsed_vfrdet_0 @ 000002a106f21200] VFR:0.000000 (0/6)

Sorry for long code.

ffprobe before.mp4 	ffprobe after.mp4 
-select_streams v 	-select_streams v 
-show_entries frame=	-show_entries frame=
coded_picture_number,	coded_picture_number,
pkt_pts_time -of 	pkt_pts_time -of 
csv=p=0:nk=1 -v 0	csv=p=0:nk=1 -v 0
0.000000,0		0.000000,0
0.016667,0		0.016667,0
0.033333,0		0.033333,0
0.050000,0		0.050000,0
0.066667,0		0.066667,0
0.083333,0		0.083333,0
0.100000,0		0.100000,0
0.116992,0		0.116667,0
0.133659,0		0.133333,0
0.150326,0		0.150000,0
0.166992,0		0.166667,0
0.183659,0		0.183333,0
0.200326,0		0.200000,0
0.216992,0		0.216667,0
0.233659,0		0.233333,0
0.250326,0		0.250000,0
0.266992,0		0.266667,0
0.283659,0		0.283333,0
0.300326,0		0.300000,0
0.316992,0		0.316667,0
0.333659,0		0.333333,0
0.350326,0		0.350000,0
0.366992,0		0.366667,0
0.383659,0		0.383333,0
0.400326,0		0.400000,0
0.416992,0		0.416667,0
0.433659,0		0.433333,0
0.450326,0		0.450000,0
0.466992,0		0.466667,0
0.483659,0		0.483333,0
0.500326,0		0.500000,0
0.516992,0		0.516667,0
0.533659,0		0.533333,0
0.550977,0		0.550000,0
0.567643,0		0.566667,0
0.584310,0		0.583333,0
0.600977,0		0.600000,0
0.617643,0		0.616667,0
0.634310,0		0.633333,0
0.650977,0		0.650000,0
0.667643,0		0.666667,0
0.685026,0		0.683333,0
0.701693,0		0.700000,0
0.718359,0		0.716667,0
0.735026,0		0.733333,0
0.751693,0		0.750000,0
0.768359,0		0.766667,0
0.785026,0		0.783333,0
0.801693,0		0.800000,0
0.818359,0		0.816667,0
0.835026,0		0.833333,0
0.851693,0		0.850000,0
0.868359,0		0.866667,0
0.885026,0		0.883333,0
0.901693,0		0.900000,0
0.918359,0		0.916667,0
0.935026,0		0.933333,0
0.951693,0		0.950000,0
0.968359,0		0.966667,0
0.985026,0		0.983333,0
1.001693,0		1.000000,0
1.018359,0		1.016667,0
1.035026,0		1.033333,0
1.051693,0		1.050000,0
1.068359,0		1.066667,0
1.085026,0		1.083333,0
1.101693,0		1.100000,0
1.118359,0		1.116667,0
1.135026,0		1.133333,0
1.152018,0		1.150000,0
1.168685,0		1.166667,0
1.185352,0		1.183333,0
1.202018,0		1.200000,0
1.218685,0		1.216667,0
1.235352,0		1.233333,0
1.252018,0		1.250000,0
1.268685,0		1.266667,0
1.286003,0		1.283333,0
1.302669,0		1.300000,0
1.319336,0		1.316667,0
1.336003,0		1.333333,0
1.352669,0		1.350000,0
1.369336,0		1.366667,0
1.386003,0		1.383333,0
1.402669,0		1.400000,0
1.419336,0		1.416667,0
1.436003,0		1.433333,0
1.452669,0		1.450000,0
1.469336,0		1.466667,0
1.486003,0		1.483333,0
1.502669,0		1.500000,0
1.519336,0		1.516667,0
1.536003,0		1.533333,0
1.552669,0		1.550000,0
1.569336,0		1.566667,0
1.586003,0		1.583333,0
1.602669,0		1.600000,0
1.619336,0		1.616667,0
1.636003,0		1.633333,0
1.652669,0		1.650000,0
1.669336,0		1.666667,0
1.686003,0		1.683333,0
1.702669,0		1.700000,0
1.719336,0		1.716667,0
1.736003,0		1.733333,0
1.752669,0		1.750000,0
1.769336,0		1.766667,0
1.786003,0		1.783333,0
1.802669,0		1.800000,0
1.819336,0		1.816667,0
1.836003,0		1.833333,0
1.852669,0		1.850000,0
1.869336,0		1.866667,0
1.886003,0		1.883333,0
1.902995,0		1.900000,0
1.919661,0		1.916667,0
1.936328,0		1.933333,0
1.952995,0		1.950000,0
1.969661,0		1.966667,0
1.986328,0		1.983333,0
2.002995,0		2.000000,0
2.019661,0		2.016667,0
2.036328,0		2.033333,0
2.052995,0		2.050000,0
2.069661,0		2.066667,0
2.086328,0		2.083333,0
2.102995,0		2.100000,0
2.119661,0		2.116667,0
2.136328,0		2.133333,0
2.152995,0		2.150000,0
2.169661,0		2.166667,0
2.186328,0		2.183333,0
2.202995,0		2.200000,0
2.219661,0		2.216667,0
2.236328,0		2.233333,0
2.252995,0		2.250000,0
2.269661,0		2.266667,0
2.286328,0		2.283333,0
2.302995,0		2.300000,0
2.319661,0		2.316667,0
2.336328,0		2.333333,0
2.352995,0		2.350000,0
2.369661,0		2.366667,0
2.386328,0		2.383333,0
2.402995,0		2.400000,0
2.419661,0		2.416667,0
2.436328,0		2.433333,0
2.452995,0		2.450000,0
2.469661,0		2.466667,0
2.486979,0		2.483333,0
2.503646,0		2.500000,0
2.520313,0		2.516667,0
2.536979,0		2.533333,0
2.553646,0		2.550000,0
2.570312,0		2.566667,0
2.586979,0		2.583333,0
2.603646,0		2.600000,0
2.620312,0		2.616667,0
2.636979,0		2.633333,0
2.653646,0		2.650000,0
2.670313,0		2.666667,0
2.686979,0		2.683333,0
2.703646,0		2.700000,0
2.720312,0		2.716667,0
2.736979,0		2.733333,0
2.753646,0		2.750000,0
2.770313,0		2.766667,0
2.786979,0		2.783333,0
2.803646,0		2.800000,0
2.820312,0		2.816667,0
2.836979,0		2.833333,0
2.853646,0		2.850000,0
2.870312,0		2.866667,0
2.886979,0		2.883333,0
2.903646,0		2.900000,0
2.920313,0		2.916667,0
2.936979,0		2.933333,0
2.953971,0		2.950000,0
2.970638,0		2.966667,0
2.987305,0		2.983333,0
3.003971,0		3.000000,0
3.020638,0		3.016667,0
3.037305,0		3.033333,0
3.053971,0		3.050000,0
3.070638,0		3.066667,0
3.088021,0		3.083333,0
3.104687,0		3.100000,0
3.121354,0		3.116667,0
3.138021,0		3.133333,0
3.154688,0		3.150000,0
3.171354,0		3.166667,0
3.188021,0		3.183333,0
3.204687,0		3.200000,0
3.221354,0		3.216667,0
3.238021,0		3.233333,0
3.254687,0		3.250000,0
3.271354,0		3.266667,0
3.288021,0		3.283333,0
3.304688,0		3.300000,0
3.321354,0		3.316667,0
3.338021,0		3.333333,0
3.354687,0		3.350000,0
3.371354,0		3.366667,0
3.388021,0		3.383333,0
3.404688,0		3.400000,0
3.421354,0		3.416667,0
3.438021,0		3.433333,0
3.454687,0		3.450000,0
3.471354,0		3.466667,0
3.488021,0		3.483333,0
3.504687,0		3.500000,0
3.521354,0		3.516667,0
3.538021,0		3.533333,0
3.554688,0		3.550000,0
3.571354,0		3.566667,0
3.588021,0		3.583333,0
3.604687,0		3.600000,0
3.621354,0		3.616667,0
3.638021,0		3.633333,0
3.654688,0		3.650000,0
3.671354,0		3.666667,0
3.688021,0		3.683333,0
3.705013,0		3.700000,0
3.721680,0		3.716667,0
3.738346,0		3.733333,0
3.755013,0		3.750000,0
3.771680,0		3.766667,0
3.788346,0		3.783333,0
3.805013,0		3.800000,0
3.821680,0		3.816667,0
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3.855013,0		3.850000,0
3.871680,0		3.866667,0
3.888346,0		3.883333,0
3.905013,0		3.900000,0
3.921680,0		3.916667,0
3.938346,0		3.933333,0
3.955013,0		3.950000,0
3.971680,0		3.966667,0
3.988346,0		3.983333,0
4.005013,0		4.000000,0
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4.038346,0		4.033333,0
4.055013,0		4.050000,0
4.071680,0		4.066667,0
4.088346,0		4.083333,0
4.105013,0		4.100000,0
4.121680,0		4.116667,0
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4.155013,0		4.150000,0
4.171680,0		4.166667,0
4.188346,0		4.183333,0
4.205013,0		4.200000,0
4.221680,0		4.216667,0
4.238346,0		4.233333,0
4.255013,0		4.250000,0
4.271680,0		4.266667,0
4.288997,0		4.283333,0
4.305664,0		4.300000,0
4.322331,0		4.316667,0
4.338997,0		4.333333,0
4.355664,0		4.350000,0
4.372331,0		4.366667,0
4.388997,0		4.383333,0
4.405664,0		4.400000,0
4.422331,0		4.416667,0
4.438997,0		4.433333,0
4.455664,0		4.450000,0
4.472331,0		4.466667,0
4.488997,0		4.483333,0
4.505664,0		4.500000,0
4.522331,0		4.516667,0
4.538997,0		4.533333,0
4.555664,0		4.550000,0
4.572331,0		4.566667,0
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4.605664,0		4.600000,0
4.622331,0		4.616667,0
4.638997,0		4.633333,0
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4.688997,0		4.683333,0
4.705664,0		4.700000,0
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4.989974,0		4.983333,0
5.006641,0		5.000000,0
5.023307,0		5.016667,0
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5.056641,0		5.050000,0
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5.106641,0		5.100000,0
5.123307,0		5.116667,0
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5.156641,0		5.150000,0
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5.189974,0		5.183333,0
5.206641,0		5.200000,0
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5.356641,0		5.350000,0
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5.823698,0		5.816667,0
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6.507682,0		6.500000,0
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6.558008,0		6.550000,0
6.574674,0		6.566667,0
6.591341,0		6.583333,0
6.608008,0		6.600000,0
6.624674,0		6.616667,0
6.641341,0		6.633333,0
6.658008,0		6.650000,0
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6.775326,0		6.766667,0
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6.808659,0		6.800000,0
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6.875326,0		6.866667,0
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6.908659,0		6.900000,0
6.925326,0		6.916667,0
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6.991992,0		6.983333,0
7.008659,0		7.000000,0
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7.125326,0		7.116667,0
7.141992,0		7.133333,0
7.158659,0		7.150000,0
7.175326,0		7.166667,0

The first 7 frames = the first clip. All the timestamps are fine for it. The second clip was concatenated with wrong timestamp.

There is no reason for VFR when concatenating CFR with stream copy. I suppose ffmpeg has a bug in concat function, it adds jitter.

I need another tool for concatenation. As I know mp4box has a limit of 20 files for -cat operations. I need to concat thousands. Do you know how I can do that? I thought it's a trivial thing to do.

Or maybe you know how to set the "distance" between the last frame of the previous clip and the first frame of the next clip in ffmpeg concat?

[poisondeathray]

The first 7 frames = the first clip. All the timestamps are fine for it. The second clip was concatenated with wrong timestamp.

There is no reason for VFR when concatenating CFR with stream copy. I suppose ffmpeg has a bug in concat function, it adds jitter.

I mentioned that earlier - when you have no audio, the 2nd video has "jitter" in the timestamps. There should be no reason why 2 separate CFR video only streams become VFR when appended. In that example, is there a sync issue? You can't tell because you have no audio stream

But when you have audio, there might be a reason for VFR - e.g. audio or video slightly shorter or longer on one or more files. The more clips, the more out of sync it can potentially become. Each individual clip might have slight "overhang" for either audio or video. No problem for 1 clip. But when you join them, you will get gaps unless you correct for them. VFR is one way of doing that - it slows down or speeds up playback, to correct for that gap area

If you have something like this, then mp4box will not work perfectly either. The audio has to be perfectly cut along samples aligning to video timestamps. For 60.0fps the "granulation" is 16.6667ms per frame. If you reset the timestamps to CFR, you lose the small VFR corrections in between joins, instead assume a single average, constant frame rate and it will have sync problems

I need another tool for concatenation. As I know mp4box has a limit of 20 files for -cat operations. I need to concat thousands. Do you know how I can do that? I thought it's a trivial thing to do.

No idea ; maybe a complex batch script

Did you try it? If your clips are do not have exact with flush ends for audio and video , I expect that mp4box will not work well either. VFR would be required for sync, or you need to edit each clip so ends are flush

Or maybe you know how to set the "distance" between the last frame of the previous clip and the first frame of the next clip in ffmpeg concat?

No idea ; you can ask on the ffmpeg user board

[qo4on]

There is no audio in the input files. Audio is added after the concatenation.
The steps:

00000.mp4, 00001.mp4... - CFR no audio
ffmpeg concat... output.mp4 - no audio
add audio to output.mp4... before.mp4

I suppose at this point audio and video have exactly the same length:

Duration: 00:00:07.32, start: 0.000000, bitrate: 4293 kb/s
    Stream #0:0(und): Video: hevc (Rext) (hev1 / 0x31766568), yuv420p(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 4237 kb/s, 59.93 fps, 59.94 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 22050 Hz, mono, fltp, 120 kb/s (default)
    Metadata:
      handler_name    : SoundHandler

mp4box can't concatenate thousands clips, right?

[Sharc]

Maybe I missed something, but did you try to remux (or convert) the files into a .ts (or .m2ts) container before concatenating these intermediate .ts files? It helped here, the concatenated .mp4 is still reported as VFR by mediainfo, however audio and video stay in sync. (I didn't concatenate 100's of files though ........ ).

[qo4on]

@Sharc
Thanks for your help.
I'm trying to do this without additional encoding, converting... All I need is to change the metadata of the concatenated file (change fps without re-encoding).
Digging deep into that I fixed almost all the problems with timestamps using video_track_timescale:

ffmpeg -y -f concat -safe 0 -i file_list.txt -c copy -video_track_timescale 60 out.mp4

frame=  431 fps=0.0 q=-0.0 Lsize=N/A time=00:00:07.20 bitrate=N/A speed=10.6x
video:226kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[Parsed_vfrdet_0 @ 00000267b58ab100] VFR:0.004651 (2/428) min: 1 max: 2 avg: 1

Stream #0:0(und): Video: hevc (Rext) (hev1 / 0x31766568), yuv420p(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 4232 kb/s,
59.86 fps, 60 tbr, 60 tbn, 60 tbc (default)

With video_track_timescale 60 I have only 1 wrong timestamp.
When I set video_track_timescale 15360 (input clip value) I have 30-40 wrong timestamps.

Finally the problem is:
I have one file with wrong timestamps and wrong fps.
I need to rearrange the timestamps to constant frame rate without reencoding.

if anybody knows how to do that (preferably using ffmpeg) please tell.

@poisondeathray
1. How can I make mp4fpsmod work even when the video file was already opened? When I try to run it on Windows and the video file is open in mpc-hc I see the error:

Reading MP4 stream...
libmp4v2: mp4v2::impl::MP4File::Open: open(C:\video.mp4) failed (..\..\mp4v2\src\mp4file.cpp,371)

ffmpeg can replace the file even if it is opened.