Grid/mosaic view RTSP streams with ffmpeg based on https://trac.ffmpeg.org/wiki/Create%20a%20mosaic%20out%20of%20several%20input%20videos

mosaic-live-6ch-substream.sh

#!/bin/bash

ffmpeg -rtsp_transport tcp \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/102 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/202 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/302 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/402 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/502 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/602 \
    -filter_complex "
		nullsrc=size=1920x1080 [base];
        [0:v] setpts=PTS-STARTPTS, scale=w=960:h=360 [upperleft];
        [1:v] setpts=PTS-STARTPTS, scale=w=960:h=360 [upperright];
        [2:v] setpts=PTS-STARTPTS, scale=w=960:h=360 [middleleft];
        [3:v] setpts=PTS-STARTPTS, scale=w=960:h=360 [middleright];
        [4:v] setpts=PTS-STARTPTS, scale=w=960:h=360 [lowerleft];
        [5:v] setpts=PTS-STARTPTS, scale=w=960:h=360 [lowerright];
        [base][upperleft] overlay=x=0:y=0 [tmp1];
        [tmp1][upperright] overlay=x=960:y=0 [tmp2];
        [tmp2][middleleft] overlay=x=0:y=360 [tmp3];
        [tmp3][middleright] overlay=x=960:y=360 [tmp4];
        [tmp4][lowerleft] overlay=x=0:y=720 [tmp5];
        [tmp5][lowerright] overlay=x=960:y=720
	" \
	-c:v rawvideo -f nut - | mpv -

mosaic-live-8ch-substream.sh

#!/bin/bash

# 8 channel input, 4 rows and 2 columns layout
ffmpeg -rtsp_transport tcp \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/102 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/202 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/302 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/402 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/502 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/602 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/702 \
    -i rtsp://smartiptv:[email protected]/Streaming/Channels/802 \
    -filter_complex "
		nullsrc=size=1920x1080 [base];
        [0:v] setpts=PTS-STARTPTS, scale=w=960:h=270 [upperleft];
        [1:v] setpts=PTS-STARTPTS, scale=w=960:h=270 [upperright];
        [2:v] setpts=PTS-STARTPTS, scale=w=960:h=270 [middleleft];
        [3:v] setpts=PTS-STARTPTS, scale=w=960:h=270 [middleright];
        [4:v] setpts=PTS-STARTPTS, scale=w=960:h=270 [lowerleft];
        [5:v] setpts=PTS-STARTPTS, scale=w=960:h=270 [lowerright];
        [6:v] setpts=PTS-STARTPTS, scale=w=960:h=270 [centerleft];
        [7:v] setpts=PTS-STARTPTS, scale=w=960:h=270 [centerright];
        [base][upperleft] overlay=x=0:y=0 [tmp1];
        [tmp1][upperright] overlay=x=960:y=0 [tmp2];
        [tmp2][middleleft] overlay=x=0:y=270 [tmp3];
        [tmp3][middleright] overlay=x=960:y=270 [tmp4];
        [tmp4][lowerleft] overlay=x=0:y=540 [tmp5];
        [tmp5][lowerright] overlay=x=960:y=540 [tmp6];
        [tmp6][centerleft] overlay=x=0:y=810 [tmp7];
        [tmp7][centerright] overlay=x=960:y=810
	" \
	-c:v rawvideo -f nut - | mpv -

mosaic-live-stream.sh

ffmpeg -rtsp_transport tcp \
    -i rtsp://smartiptv:[email protected]:6911/Streaming/Channels/101 \
    -i rtsp://smartiptv:[email protected]:6911/Streaming/Channels/201 \
    -i rtsp://smartiptv:[email protected]:6911/Streaming/Channels/301 \
    -i rtsp://smartiptv:[email protected]:6911/Streaming/Channels/401 \
    -filter_complex "
		nullsrc=size=1920x1080 [base];
		[0:v] setpts=PTS-STARTPTS, scale=960x540 [upperleft];
		[1:v] setpts=PTS-STARTPTS, scale=960x540 [upperright];
		[2:v] setpts=PTS-STARTPTS, scale=960x540 [lowerleft];
		[3:v] setpts=PTS-STARTPTS, scale=960x540 [lowerright];
		[base][upperleft] overlay=shortest=1 [tmp1];
		[tmp1][upperright] overlay=shortest=1:x=960 [tmp2];
		[tmp2][lowerleft] overlay=shortest=1:y=540 [tmp3];
		[tmp3][lowerright] overlay=shortest=1:x=960:y=540
	" \
	-c:v libx264 -preset superfast -crf 18 -f matroska - | ffplay -

mosaic-live-substream.sh

ffmpeg -rtsp_transport tcp \
    -i rtsp://smartiptv:[email protected]:6911/Streaming/Channels/102 \ # use substream with lower resolution
    -i rtsp://smartiptv:[email protected]:6911/Streaming/Channels/202 \
    -i rtsp://smartiptv:[email protected]:6911/Streaming/Channels/302 \
    -i rtsp://smartiptv:[email protected]:6911/Streaming/Channels/402 \
    -filter_complex "
		nullsrc=size=1920x1080 [base];
		[0:v] setpts=PTS-STARTPTS, scale=960x540 [upperleft];
		[1:v] setpts=PTS-STARTPTS, scale=960x540 [upperright];
		[2:v] setpts=PTS-STARTPTS, scale=960x540 [lowerleft];
		[3:v] setpts=PTS-STARTPTS, scale=960x540 [lowerright];
		[base][upperleft] overlay=shortest=1 [tmp1];
		[tmp1][upperright] overlay=shortest=1:x=960 [tmp2];
		[tmp2][lowerleft] overlay=shortest=1:y=540 [tmp3];
		[tmp3][lowerright] overlay=shortest=1:x=960:y=540
	" \
	-c:v libx265 \ # check output and see what format the camera use, see `ffmpeg -encoders | grep V`
	-preset superfast -crf 18 -f matroska - | ffplay -

Tried with c:v copy -crf 18 -f matroska - | ffplay - but didn't work for me.

OK, but why don't use FFPLAY directly in place of piped FFMPEG instead ?
Check here: https://stackoverflow.com/questions/68824225/bad-ffmpeg-performace-compared-to-ffplay-and-vlc

About HW accelleration, check out these interesting posts:

• https://video.stackexchange.com/questions/25078/improve-performance-on-4-x-4k-mosaic-with-ffmpeg
• https://stackoverflow.com/questions/11552565/vertically-or-horizontally-stack-mosaic-several-videos-using-ffmpeg

...@cpcloud's ffgrid.sh may inspire too.
Another cool approach is cinegrid by @s7sost.

Someone suggests to use xstack filter for better performances:

• https://ffmpeg.org/ffmpeg-filters.html#xstack
• https://trac.ffmpeg.org/wiki/Create%20a%20mosaic%20out%20of%20several%20input%20videos%20using%20xstack
• https://stackoverflow.com/questions/11552565/vertically-or-horizontally-stack-mosaic-several-videos-using-ffmpeg
• http://underpop.online.fr/f/ffmpeg/help/xstack.htm.gz

Last but not least, it would be great to let FFMPEG get the screen resolution and adapt the mosaic (and source videos) to it:
https://superuser.com/questions/841235/how-do-i-use-ffmpeg-to-get-the-video-resolution

EDIT:
Just played a bit with ffplay and this seems to work flawlessly with local files...
@ffplay -autoexit -f lavfi "movie=<filename1>:seek_point=0.0, drawtext=verdana.ttf:text='TEST':fontcolor=white:fontsize=24:box=1:[email protected]:boxborderw=5:x=(w-text_w)/2:y=(h-text_h)-5, scale=960:-1, setpts=PTS-STARTPTS[v0];movie=<filename2>:seek_point=0.0, scale=960:-1, setpts=PTS-STARTPTS[v1];[v0][v1]hstack"

Hope that inspires !