Convert 3GA to MKV — Free Online Converter

MKV (Matroska Video) is the most flexible open-source multimedia container, capable of holding virtually any combination of audio, video, subtitle, and metadata streams. While MKV is primarily known as a video format popular in the media enthusiast community, it can also serve as a powerful audio container when you need features that simpler formats lack — such as multiple audio tracks, embedded subtitles for transcription, chapter markers, and extensive metadata tagging.

Converting 3GA audio from old Samsung or LG phones to MKV is an unusual but technically sound operation. The AMR audio is transcoded to a universally supported codec like AAC or Opus and wrapped in the MKV container. This is relevant for media library managers like Plex, Jellyfin, and Kodi that are configured to work with MKV files, or for users who want to embed transcription subtitles alongside their converted voice recordings in a single container file.

MKV's standout feature is its ability to carry multiple streams in one file. If you have old phone recordings that you want to pair with text transcriptions, translations, or chapter markers for navigation, MKV is the only common container format that supports all of these features simultaneously. A single MKV file can contain the converted audio plus an SRT subtitle track with the transcription, making it a self-contained audio-with-text document.

MKV is also the preferred format for media server software. Plex, Jellyfin, Emby, and Kodi all handle MKV files as first-class citizens with full metadata scraping, chapter navigation, and subtitle support. If you maintain a home media server and want to add converted voice recordings from old 3G-era phones to your library alongside your music and video collection, MKV integrates naturally with your existing infrastructure.

FFmpeg decodes the AMR audio from the 3GA container and re-encodes it as AAC (192 kbps) or Opus (128 kbps) inside the MKV (Matroska) container. MKV does not natively support AMR, so transcoding is required. The Matroska container supports an unlimited number of audio, video, and subtitle tracks with chapter navigation and rich metadata. The output uses WebM-compatible codecs by default for maximum player support. MKV files use EBML (Extensible Binary Meta Language) structure for efficient seeking and streaming.