With Converter App, you can convert 3GPP files into many other formats:
3GPP to MP4 | 3GPP to MP3 | 3GPP to MOV | 3GPP to WEBM | 3GPP to AVI | 3GPP to WAV | 3GPP to M4A | 3GPP to OGG
→ All 3GPP Converters
If you want to keep working with your final MKV, try:
MKV to MP4 | MKV to MP3 | MKV to SRT | MKV to MOV | MKV to WEBM | MKV to AVI | MKV to WMV | MKV to MPG
→ All MKV Converters