Caption/subtitle processing library with multi-format support (SRT, VTT, ASS, TTML, TextGrid, NLE formats)
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lattifai-captions
Caption/subtitle processing library with comprehensive format support.
Features
- Multi-format support: SRT, VTT, ASS, SSA, TTML, TextGrid, LRC, SRV3, and more
- YouTube formats: SRV3 (YTT v3), YouTube VTT with word-level timestamps
- Professional NLE formats: Avid DS, Final Cut Pro XML, Premiere Pro XML, Adobe Audition
- Word-level timing: Karaoke-style word-by-word timestamps
- Standardization: Netflix/BBC broadcast guidelines compliance
- Sentence splitting: AI-powered intelligent sentence segmentation
- Zero dependencies on heavy ML frameworks: Lightweight and fast
Installation
# Basic installation
pip install lattifai-captions
# With sentence splitting support
pip install lattifai-captions[splitting]
Quick Start
from lattifai.caption import Caption
# Read a caption file
caption = Caption.read("input.srt")
# Write to different format
caption.write("output.vtt")
# Convert to string
vtt_content = caption.to_string("vtt")
# Access segments
for segment in caption.supervisions:
print(f"{segment.start:.2f} - {segment.end:.2f}: {segment.text}")
Supported Formats
Input/Output (Read & Write)
| Format | Extensions | Description |
|---|---|---|
| SRT | .srt |
SubRip subtitle format |
| VTT | .vtt |
WebVTT, includes YouTube VTT with word-level timestamps |
| ASS/SSA | .ass, .ssa |
Advanced SubStation Alpha |
| SRV3 | .srv3, .ytt |
YouTube Timed Text v3 with word-level timing |
| SBV | .sbv |
YouTube SubViewer format |
| SUB | .sub |
MicroDVD subtitle format |
| SAMI | .sami, .smi |
SAMI subtitle format |
| JSON | .json |
Structured data with word-level support |
| CSV/TSV | .csv, .tsv |
Tabular formats |
| TextGrid | .textgrid |
Praat TextGrid format |
| LRC | .lrc |
Lyrics format with word-level timestamps |
| Gemini | .md |
Gemini AI transcript markdown |
Output Only
| Format | Extensions | Description |
|---|---|---|
| TTML | .ttml |
Timed Text Markup Language (W3C standard) |
| IMSC1 | .ttml |
Netflix/streaming TTML profile |
| EBU-TT-D | .ttml |
European broadcast TTML profile |
| Avid DS | .txt |
Avid Media Composer SubCap |
| FCPXML | .fcpxml |
Final Cut Pro XML |
| Premiere XML | .xml |
Adobe Premiere Pro XML |
| Audition CSV | .csv |
Adobe Audition markers |
| EdiMarker CSV | .csv |
Pro Tools markers |
Word-Level Timing
Many formats support word-level timing for karaoke-style output:
from lattifai.caption import Caption
caption = Caption.read("input.srv3") # SRV3 has built-in word timing
# Access word-level alignment
for segment in caption.supervisions:
if segment.alignment and "word" in segment.alignment:
for word in segment.alignment["word"]:
print(f" {word.symbol}: {word.start:.3f}s - {word.end:.3f}s")
# Export with word-level timing
caption.write("output.json", word_level=True) # JSON preserves words array
caption.write("output.ass", word_level=True, karaoke_config=KaraokeConfig(enabled=True))
YouTube SRV3 Format
SRV3 is YouTube's proprietary timed text format with millisecond-precision word timing:
from lattifai.caption import Caption
# Read SRV3 (automatically extracts word-level timing)
caption = Caption.read("video.srv3")
# Convert to other formats
caption.write("output.srt") # Standard SRT
caption.write("output.vtt", word_level=True) # VTT with word timing
caption.write("output.srv3", word_level=True) # Back to SRV3
SRV3 structure example:
<timedtext format="3">
<body>
<p t="240" d="6559" w="1">
<s ac="0">Does</s>
<s t="320" ac="0"> fast</s>
<s t="560" ac="0"> charging</s>
</p>
</body>
</timedtext>
Sentence Splitting
Split captions into natural sentences (requires [splitting] extra):
from lattifai.caption import Caption, SentenceSplitter
# Using Caption method
caption = Caption.read("input.srt")
split_caption = caption.split_sentences()
# Or use SentenceSplitter directly
splitter = SentenceSplitter()
split_supervisions = splitter.split_sentences(caption.supervisions)
Format Conversion
from lattifai.caption import Caption
# Read any format
caption = Caption.read("input.srt")
# Write to any supported format
caption.write("output.vtt")
caption.write("output.ass")
caption.write("output.json")
caption.write("output.srv3", word_level=True)
caption.write("output.ttml")
# Or get as string
srt_content = caption.to_string("srt")
json_content = caption.to_string("json", word_level=True)
Standardization
Apply broadcast standards to captions:
from lattifai.caption import Caption, CaptionStandardizer
standardizer = CaptionStandardizer(
min_duration=0.7, # Minimum segment duration
max_duration=7.0, # Maximum segment duration
min_gap=0.08, # Minimum gap between segments
max_lines=2, # Maximum lines per segment
max_chars_per_line=42, # Maximum characters per line
)
caption = Caption.read("input.srt")
standardized = standardizer.process(caption.supervisions)
Validation
Check captions against quality standards:
from lattifai.caption import Caption, CaptionValidator
validator = CaptionValidator(
min_duration=0.7,
max_duration=7.0,
min_gap=0.08,
max_chars_per_line=42,
)
caption = Caption.read("input.srt")
result = validator.validate(caption.supervisions)
print(f"Valid: {result.valid}")
print(f"Average CPS: {result.avg_cps:.1f}")
print(f"Max CPL: {result.max_cpl}")
print(f"Warnings: {result.warnings}")
API Reference
Caption Class
from lattifai.caption import Caption
# Class methods
Caption.read(path, format=None, normalize_text=True)
Caption.from_string(content, format)
Caption.from_supervisions(supervisions, language=None, metadata=None)
# Instance methods
caption.write(path, include_speaker=True, word_level=False, karaoke_config=None)
caption.to_string(format, include_speaker=True, word_level=False, karaoke_config=None)
caption.split_sentences()
caption.shift_time(seconds)
# Properties
caption.supervisions # List[Supervision]
caption.duration # Total duration in seconds
caption.language # Language code
caption.source_format # Original format
Supervision Class
from lattifai.caption import Supervision
sup = Supervision(
start=0.0, # Start time in seconds
duration=2.5, # Duration in seconds
text="Hello world", # Caption text
speaker="Alice", # Optional speaker label
alignment=None, # Optional word-level alignment
)
# Properties
sup.end # start + duration
sup.text # Caption text
sup.speaker # Speaker label
sup.alignment # Dict with "word" key containing AlignmentItem list
License
Apache-2.0
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