To concatenate two MP4 files using FFmpeg, you can follow the steps below:

    Open a command prompt or terminal window.

    Navigate to the directory where your MP4 files are stored using the "cd" command.

    Run the following FFmpeg command to concatenate the two MP4 files:

```css
ffmpeg -i input1.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts
```

This command will convert the first input file (input1.mp4) into an intermediate transport stream file (intermediate1.ts) in MPEGTS format.

Run the following command to convert the second input file (input2.mp4) into another intermediate transport stream file (intermediate2.ts):

```css
ffmpeg -i input2.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate2.ts
```
Run the following command to concatenate the two intermediate transport stream files into a single MP4 file:

```go
ffmpeg -i "concat:intermediate1.ts|intermediate2.ts" -c copy output.mp4
```
This command will concatenate the two intermediate transport stream files (intermediate1.ts and intermediate2.ts) using the "concat" protocol and copy the video and audio codecs without re-encoding (-c copy) to create the output file (output.mp4).

After the command is complete, you should have a single MP4 file (output.mp4) that contains the concatenated content of the two input files (input1.mp4 and input2.mp4).

Note: The "-bsf:v h264_mp4toannexb" option is necessary to ensure compatibility with some video players that require the H.264 video codec to be in the Annex B format. If you encounter any issues with playback after concatenating your MP4 files, you may need to use this option or try another codec.
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