Conversion is not remuxing
A container conversion rewrites the video stream. Remuxing only moves existing streams into a new wrapper, which is faster and lossless, and it belongs in the stream-copy and media packaging hub. You are in the right place when the destination cannot accept the codec at all, for example an editor that refuses HEVC inside AVI, a web pipeline that wants VP9 in WebM, or an archive standard written around Matroska. Accept that a real transcode is happening, and treat its quality settings as first-class decisions.
Normalize inbound formats into MP4
Old projects arrive as AVI, rescued recordings as FLV, downloads as MKV, and camera output as MOV. Converting each into MP4 first gives the pipeline one common baseline that every downstream tool accepts. Work from the highest-quality source available, because every re-encode spends quality that later steps cannot recover.
Choose the outbound container by destination
The target container is a requirement, not a preference. MOV keeps Apple editing suites happy, MKV preserves many audio and subtitle tracks for archival masters, WebM delivers VP9 to web players, and AVI or FLV serve legacy chains that refuse anything newer. When nothing forces a special container, stay with MP4. Note the requirement next to the output so the choice survives the project.
Own the re-encode settings
Re-encoding with defaults hides the decisions that matter. A CRF step fixes quality per frame and lets size float, while a bitrate target fixes size and lets quality float. Pick the mode that matches your constraint, test one clip with dark scenes and fast motion, and write down the passing settings. Then bring oversized results back inside budget with compression or destination-aware optimization rather than re-rolling the conversion blind.
Batch with one recorded configuration
Converting a series file by file invites drift, because each episode ends up encoded under slightly different settings. Set the target format and quality configuration once, run the library through the batch converter, and enforce a shared size ceiling with batch compression. Verify the first output in the real destination player before letting the full batch run, and keep the recorded settings with the delivered files so the run can be reproduced.