# Speed, caching and housekeeping


# Speed

Synthesis runs at roughly **4.6× realtime** on an M-series Mac with `af_heart`.

It is also cached per chunk, keyed on the text, the voice, the speed and the model. Re-running a document you edited re-synthesizes only what changed: a 22-minute paper re-renders in **8 seconds** instead of 4 minutes 54.

That is what makes the edit-and-republish loop in [The pipeline](the-pipeline.md) practical.

``` bash
earmark audio paper.pdf --dry-run    # chunk count and duration, no synthesis
earmark audio paper.pdf --no-cache   # ignore and don't write the cache
earmark audio paper.pdf --refresh    # re-extract and re-synthesize from scratch
```

The cache trims itself after every `audio` run: entries untouched for 90 days go, and the least recently used go after that if it passes 2 GB. It lives with your application data, not in the library.

`earmark config --show` prints where the cache and the model actually are.


# Housekeeping

``` bash
earmark feed --check                  # do the published URLs actually serve?
earmark feed --rebuild                # rewrite feed.xml and the cover
earmark feed --prune --keep 20        # drop all but the newest 20
earmark feed --prune --max-size 800MB
earmark feed --prune --orphans        # delete files the feed no longer lists
```

`--prune` needs one of `--keep` or `--max-size`; it will not guess.


## `--orphans`

Pruning an episode removes it from the feed. `--orphans` goes further and deletes library files the feed no longer lists: the leftover MP3s and Markdown from episodes that have already been dropped.

It is the one destructive flag here, so it only runs alongside `--prune`. `cover.jpg` is never treated as an orphan.


## Rebuilding

`--rebuild` rewrites `feed.xml` and the cover from the current settings without re-synthesizing anything. Run it after changing a title, an author, a description, or the cover image.

Full flag list: [`earmark feed`](../reference/feed.md).