refactor: frame converter and mp4 track improvements

- Refactor frame converter implementation
- Update mp4 track to use ICodex
- General refactoring and code improvements

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

example/default/main.go

@@ -7,13 +7,11 @@ import (
 	"m7s.live/v5"
 	_ "m7s.live/v5/plugin/cascade"
 
-	_ "m7s.live/v5/plugin/crypto"
 	_ "m7s.live/v5/plugin/debug"
 	_ "m7s.live/v5/plugin/flv"
 	_ "m7s.live/v5/plugin/gb28181"
 	_ "m7s.live/v5/plugin/hls"
 	_ "m7s.live/v5/plugin/logrotate"
-	_ "m7s.live/v5/plugin/monitor"
 	_ "m7s.live/v5/plugin/mp4"
 	_ "m7s.live/v5/plugin/onvif"
 	_ "m7s.live/v5/plugin/preview"