Over time I have repeatedly tried to create a script that would take the various media + external audio collected in a folder, do audio/video synchronization, and then delete the internal audio tracks and replace them with the external one. I thought it could be done with ffmpeg and its feature. Unfortunately, I do not have the capability and have always failed. One could also introduce, in such a script, the concatenation of the files.

1- collect the files into one folder (video files+internal audio; external audio).
2- Synchronize the files with the external audio track (your choice of timecode or waveform).
3- Duplicate and break the external audio track so that there are coincidental chunks with the various files.
4- Associate the audio clips with the relevant files.
5- Delete the internal audio tracks leaving only the external one.
6- Concatenate the files for each camera/scene with which they were recorded (also leaving blanks if they are not strictly consecutive).

I guess it would be a real program rather than a simple script.

@Kabak wrote:
When you use "cat" command, you join the files,
the packet is entire so it's work fine

Good! The "cat" command do the work! Good to know for MTS files by Panasonic. Thanks!

For the other questions about Multicam, are you in the right way?

It use FUSE to make the virtual file. No need loosing disk space and time in files concatenation or making big modification to cinelerra. This methods build the result file few seconds and work fine.

With this, i think we can build a specific assistant to import those files by selecting necessary files and group them.
It seem to be also possible to automatically group the different record from a camera by using metadata (is start date/hour + duration similar to next file) and by using MTS packet counter (4 bits counter, little after sync character 1/16 probability of wrong detection).

In my real case, one camera with 14 files from 4 record loaded in less of 1 minute for an single will be a huge improvement.

01150.MTS and 01150-01151 start are perfectly aligned
01151.MTS and 01150-01151 ends are perfectly aligned (checked with spotlights switching)

When you see info from the media, you see there is frame missing (1629 + 17277 = 18906 <> 18909 ):

01150-01151.MTS
1 video stream
Vid0 (0), id 0x00001b:
video1 h264 1920x1080 25.00 pix yuv420p
interlace (container level): 2
interlace (codec level): -1
color space:unknown/ range:unknown
codec Detected SAR: 1:1 , DAR 16:9
18909+0 frms 756.34 secs 0:12:36.34


01150.MTS
1 video stream
Vid0 (0), id 0x00001b:
video1 h264 1920x1080 25.00 pix yuv420p
interlace (container level): 2
interlace (codec level): -1
color space:unknown/ range:unknown
codec Detected SAR: 1:1 , DAR 16:9
17277+0 frms 691.06 secs 0:11:31.06


01151.MTS
1 video stream
Vid0 (0), id 0x00001b:
video1 h264 1920x1080 25.00 pix yuv420p
interlace (container level): 2
interlace (codec level): -1
color space:unknown/ range:unknown
codec Detected SAR: 1:1 , DAR 16:9
1629+0 frms 65.14 secs 0:01:05.14

MPEG transportation stream use packets so i think you have something like that :
File 1 : Packet x : Frame A1, A2, A3
File 1 : Packet y : Frame B1, partial B2
File 2 : Packet y : Frame Partial B2, B3
File 2 : Packet z : Frame C1, C2, C3

Packet y is split between two files so CRC integrity failed and so the frames B1, B2, B3 are lost.

When you use "cat" command, you join the files, the packet is entire so it's work fine.

AAAAA
    ABBBBBC
          CCCCCC

I got 404 error from the link : https://cinelerra-gg.org/download/testing/cinelerra-forum.zip 🤔

But this is all misleading with respect to your problems with multicam, it was better if I didn't talk about it.

Maybe, maybe not.

If we want to build an easier workflow, it can have a place.

If you can find a good workflow and remedy the loss of frame/sync, let us know, that we will improve the manual.

I will tell you.

For the lost frames with splitted MTS file, it's seem to be an know issue with many softwares (even ffmpeg) so i think it must be treated when we load it into the media window.

We will know if i can make "test files" for this part.

My big concern is about sending those file due to my low bandwidth. About 20 hours if i didn't have interruption. Some FTP can't resume file transfer, transferring 700mb file is already a challenge on them. Maybe using torrent ?