This feature allows you to download a file in order, from beginning to end, instead of the usual (and sometimes faster) random order.  This can be helpful if you want to start viewing the file right away, before the download completes.

In the main transfers view, simply right-click any file in the bottom Files tab.  From the menu, go to the Priority sub-menu, and at the bottom will be a checkbox to activate sequential downloading for that particular file.


You can adjust some of the parameters for sequential downloading, such as aggressiveness, head and tail first mode, and limits based on the number of seeds in the torrent.  Go to Settings > Transfers > Files and click the Configure button where it says "Sequential download options".  A new settings popup will open.


You can also have automatic sequential downloading for certain files types or files matching a wildcard.  This can be done in the File Auto-Select feature, which is also available from Settings > Transfers > Files.

Minimum seed count: This many seeds must be detected to activate sequential.
Aggresssiveness percent: How many pieces are downloaded according to sequential rules. 100% means strictly sequential. Whereas 50% means: 50% are in sequence and 50% are rarest-first pieces to keep a torrent healthy.
Progress limit percent: Stop sequential download rules when downloaded beyond this limit.
File tail MB: Download this many megabytes at the end of the file
File tail percent: "0.60" means "0.60%". Download whatever figure is larger: the tail MB or the tail percentage.


People usually associate the "sequential" method of download with a strictly sequential piece by piece download. This contradicts how BitTorrent expects pieces to be downloaded, namely the rarest pieces first. This approach ensures those rarest pieces don't go "extinct" within a swarm of seeders and peers (who act like partial seeders). Tixati is the only client that allows you to configure a safe trade-off between a strict sequential preset and a swarm's health.

Preset name: Soft sequential
Minimum Seed Count: 4-5. Seeds with multiple IPs (one person with IPv4 and IPv6) count as multiple seeds.
Aggressiveness percent: 50 - 80%. Lower is better for swarm health.
Progress limit percent: 50 - 80%. Lower is better for swarm health.
File Tail MB: 1 MB. Specify however much you need for file previews to work correctly.
File Tail percent: 0.60. Similar to above.


You can see an example of a custom Sequential preset and custom File Selection preset here: https://forum.tixati.com/support/8333
It will mark all files in all transfers for a safe sequential download by default.