The Photos app re-encodes the file regardless of whether the source files are similar not. Here’s the file size comparison of items merged using the Photos app Versus Avidemux. Please select a file name and save it to the desired location. You have MKV, AVI, and other formats as well in the list.

you want to join several files with differing properties (different formats, different resolution, etc.).

you want to use filters (it is impossible to filter audio or video without re-encoding it.).

you have to do precise cutting that’s not possible to do on keyframes.

you want to compress the file to a smaller size (at the expense of quality.).

you want to perform audio or video format conversion.

Encoding is also much slower than copying. If the compression is lossy (with most encoders it is), this implies quality loss. When you select an audio or video encoder, the audio or video track is re-encoded.

you want to perform technical changes like saving the video to a different container.

you want to fix constant audio/video desync (using the Shift option in the audio section.).you want to append several files (using either File→Append or the automatic appending that Avidemux provides) – if the resolution (width, height), video format, audio format, audio bitrate, and the sampling rate is the same for all files, you can use the copy mode.you want to cut out parts from the video without changing the output format.

This means it is speedy (usually a couple of minutes), and there is no quality loss. When the audio or video encoder is set to Copy, it means no re-encoding takes place, and the audio or video track from the input file is just copied to the resulting file as-is.

Avidemux windows 7