How do I reduce the file size when screen recording with internal plus external audio ??

Hey muralidhar185,

The only options available with Apple software on the Mac to reduce the file size of a screen recording, would be to edit or trim content from the video, or to export the recording in a lower resolution. There may be apps available from other companies that allow you to compress video files on your Mac as well.

You can find steps to edit or trim screen recordings here: Trim a movie or clip in QuickTime Player on Mac

"Trim a movie

1. In the QuickTime Player app  on your Mac, open the movie you want to trim, then choose Edit > Trim.
2. Drag the yellow handles in the trimming bar. The area outside of the yellow handles is the area to be trimmed. 
3. Tip: To make more precise edits, click and hold a handle to see individual frames of the clip.
4. Click Trim."

You can find options for exporting recordings in different resolutions and formats here: Export movies to other file formats and resolutions using QuickTime Player on Mac - Apple Support

"

1. In the QuickTime Player app  on your Mac, choose File > Export As, then choose an option from the Export menu.
2. This menu shows resolutions appropriate for movies based on commonly used video sizes (resolutions larger than that of your movie are dimmed). The exact resolution and data rate of an exported movie depend on the original.
3. 4K: QuickTime movie using H.264 or HEVC (H.265), up to 3840 x 2160 resolution.
4. 1080p: QuickTime movie using H.264 or HEVC (H.265), up to 1920 x 1080 resolution.
5. 720p: QuickTime movie using H.264, up to 1280 x 720 resolution.
6. 480p: QuickTime movie using H.264, up to 640 x 480 resolution.
7. Choose this option if you are exporting a movie to post online (for example, to YouTube).
8. Audio Only: An Apple MPEG 4 audio file with an AAC audio track.
9. If you chose the 4K or 1080p export resolution, click the Format pop-up menu, then do one of the following: 
10. Choose Smaller File Size to export the movie in HEVC format
11. Choose Greater Compatibility to export the movie in H.264 format.
12. You can preserve the transparency of a movie when exporting to a HEVC format. Choose File > Export As > 1080p, select Use HEVC checkbox, then select the Preserve Transparency checkbox. 
13. Note: The Preserve Transparency checkbox only appears for movies with an alpha channel, such as ProRes 4444.
14. Enter a name for your exported file and choose a destination.
15. Click Save."

Thanks!