Free online TXT to SMI converter

A television or older media player may accept SAMI subtitles but not a plain .txt file. Converting to .smi preserves usable timings only when the source already includes recognizable timestamps; untimed text must be synchronized first.

What the TXT format is

In video-subtitle workflows, .txt identifies a plain-text container, not one standardized subtitle structure. Captioning tools and manual workflows may store one caption per line, numbered entries, or timestamped blocks such as 00:01:12,500 --> 00:01:15,000.

TXT provides no universal rules for timing, speaker labels, language tracks, or line breaks. A program may interpret timestamps as seconds, milliseconds, or HH:MM:SS,mmm, while another may treat every line as untimed text. Identify the source convention before conversion. A TXT file that is actually SRT syntax with a different extension should be imported as SRT when the software supports that option.

What the SMI format is

SMI, also called SAMI, is an HTML-like subtitle format designed for synchronized captions. It stores caption start times in milliseconds inside elements such as <SYNC Start=12500>, followed by caption markup such as <P Class=ENCC>Caption line</P>.

A caption normally remains active until the next <SYNC> timestamp, which often contains an empty paragraph to end the previous caption. SAMI can contain HTML-style line breaks, character entities, styling, and separate language or caption classes. Some televisions, media players, and older subtitle applications support SMI when they do not support SRT or WebVTT.

How to convert a TXT file to SMI

Using 101convert.com:

1. Open the TXT-to-SMI converter on 101convert.com.
2. Upload the .txt file and select SMI or SAMI as the output format.
3. Choose the input interpretation, if available. Select the option matching the file, such as SRT-style timestamps, one caption per line, or millisecond timing.
4. Start the conversion and download the resulting .smi file.
5. Open the output in a subtitle editor and test it with the intended player or television. Check timing, line breaks, language characters, and the file extension.

Conversion on 101convert.com does not require installing software. The result still depends on the timing syntax and encoding used by the source TXT file.

Using Subtitle Edit:

1. Open Subtitle Edit and use File → Open to load the TXT file, or use the import method matching its actual syntax.
2. If the file is SRT-like text, import it as SRT rather than as undelimited plain text. Confirm that the entries appear correctly in the subtitle grid and timeline.
3. Correct timestamps, overlaps, reading order, line breaks, and encoding.
4. Use File → Save as and choose SAMI/SMI from the format list.
5. Reopen the saved file and test it with the target device or media player.

The exact import choice depends on the TXT structure. If it contains only sentences, enter start and end times in Subtitle Edit before exporting. No converter can derive accurate speech timing from untimed caption text.

Quality and compatibility limits

• SMI uses integer millisecond timestamps. A comma-versus-period decimal separator, a mistaken seconds-versus-milliseconds interpretation, or an unrecognized timestamp pattern can shift every caption.
• Some players expect an initial synchronization entry at time zero, sometimes with an empty caption. Add one when the target device requires it.
• Save as UTF-8 for accented, Cyrillic, Greek, or Asian characters unless the target device documents a required legacy encoding. Test the result because older televisions may support only a limited code page.
• SMI markup is not rendered identically by every player. Test <P Class=...>, line breaks, font tags, styling, and multiple-language classes on the actual playback device.
• Conversion may remove comments, speaker metadata, unsupported formatting, or timing precision. Keep the original TXT file and compare the converted captions against the video.