Because different tools write the index in different places, the concept of an "index-less" file is relative. A player optimized for streaming (expecting the index at the front) may struggle with a standard mkvmerge file (index at the back) until it builds its own in-memory index.
| Container | Index mechanism | Index location | Mandatory? | |------------|----------------|----------------|-------------| | | Cues (separate element) | Within Segment, usually near end | No, but recommended | | MP4/MOV | stco / co64 (chunk offset table) + stts (time-to-sample) | Within moov atom | Yes, for reliable seeking | | AVI | idx1 chunk | At end of file (or rec list) | No (AVI v1.0), Yes (OpenDML) | | WebM | Same as MKV Cues | Within Segment | Required for WebM compliance | mkv index
Maps timecodes to specific byte locations of video keyframes. Because different tools write the index in different
