how to merge multiple avi mjpeg files?

[marcorocchini]

Hi

but the cats. However

I wonder if is possible merge (concatenate) multiple .avi files (encoded in mjpeg) possibly via commandline. FFmpeg do it in concat mode but strangely the output .avi seems 1920X1988 and not as the source 1920X1080

My .avi source does not have audio inside

Is there an alternative? thanks

[ProWo]

I don't think fmpeg concat changes the resolution.
Check with mediainfo the resolution of each part.
Probably only the DAR is changed.

[blud7]

Maybe you are encoding and not just joining. Let's see your command line?

[marcorocchini]

were this is 2 input .avi files:

https://www.swisstransfer.com/d/b8836e07-0137-4d1c-8467-9ffe0c19ebc7

I use something like:

ffmpeg.exe -y -v quiet -stats -threads auto -f concat -safe 0 -i AllRemuxConcatList.txt -vcodec copy -an output.avi

and AllRemuxConcatList.txt is:

file 'C:\Users\Administrator\Desktop\Nuova cartella (12)\AllSingleRemuxed\DJI_0139.MP4.avi'  
file 'C:\Users\Administrator\Desktop\Nuova cartella (12)\AllSingleRemuxed\DJI_0140.MP4.avi'

but the final output.avi is 1088 and not 1080:

Generale
Nome completo : C:\Users\Administrator\Desktop\Nuova cartella (12)\outputRoutine_7_AVI_MJPG_NO_MASCHERA_BLUR.avi
Formato : AVI
Formato/Informazioni : Audio Video Interleave
Dimensione : 183MiB
Durata : 7s 80 ms
Bitrate totale : 217 Mb/s
Creato con : Lavf59.16.100

Video
ID : 0
Formato : JPEG
ID codec : MJPG
Durata : 7s 80 ms
Bitrate : 217 Mb/s
Larghezza : 1.920 pixel
Altezza : 1.088 pixel
Rapporto aspetto visualizzazione : 16:9
Frame rate : 25,000 FPS
Spazio colore : YUV
Croma subsampling : 4:2:2
Profondità bit : 8 bit
Tipo scansione : Interlacciato
Ordine scansione : Top field first
Modo compressione : Con perdita
Bit/(pixel*frame) : 4.150
Dimensione della traccia : 183MiB (100%)

[marcorocchini]

does exist something like commandline to acorrectly merge the 2 avi?

[blud7]

Yes indeed. I think ProWo on the right track.
Try merging with mkvmerge instead.

[jagabo]

I believe MJPEG is always mod 16 internally. When a 1080 (mod 8) line video is compressed the encoder internally ads 8 lines to make it 1088 (mod 16) lines. On playback it removes those extra lines. All you're seeing is some confusion about those extra lines. The video stream itself isn't changed by the append operation.

After appending you can patch the AVI headers to indicate the video is 1080 lines instead of 1088. Or you can crop away the extra 8 lines when you edit the video.

[marcorocchini]

After appending you can patch the AVI headers to indicate the video is 1080 lines instead of 1088

ah wow, but in what way?

[jagabo]

I used a hex editor to change three values near the start of the AVI file.


[Attachment 73083 - Click to enlarge]

The three red "38" used to be "40". Note that the value following them is 04. When you put the two bytes together into a word in little-endian order you get 0440 and 0438. 0440 hex is 1088 in decimal. 0438 hex is 1080 decimal. Those are the heights of the frame in the headers of the AVI file. So I changed the height of the frame from 1088 to 1080.

Useful information: https://learn.microsoft.com/en-us/windows/win32/directshow/avi-riff-file-reference

[marcorocchini]

wondeful, but is there a way to do this operation via batch?

[jagabo]

Sure, find or write a program that reads the start of the file, modifies it, then writes it back.

[marcorocchini]

yes oh my poor cat. However I need to open another tread

[jagabo]

PowerShell has the ability to patch binary files.