This file exercises many ASS format features: multiple styles, positioning, colour overrides, and various override tags. It serves as a corpus for testing ass-rs parser completeness.

`basic-styled.ass` #

A minimal hand-written ASS file for focused validation of the rendering pipeline. It covers:

Default style: Noto Sans SC, white, size 24, bottom-centre (alignment 2)
Secondary style: Noto Sans SC, yellow, size 24, top-centre (alignment 8)
Inline override tags: {\b1}bold{\b0}, {\i1}italic{\i0}
CJK text: 日本語テスト at 10 seconds

Timestamps:

0:00:01 – 0:00:04 → "Hello, world!" (Default style)
0:00:02 – 0:00:05 → "Top text" (Top style, yellow, top-centre)
0:00:03 – 0:00:06 → "Styled bold and italic" with inline tags (Default)
0:00:10 – 0:00:13 → "日本語テスト" (CJK test, requires Noto Sans SC font)

`validation-results.md` #

Documents the results of the end-to-end rendering pipeline validation, including what worked, what didn't, and known limitations.

Reference Screenshots #

Reference screenshots (from mpv/libass) have not yet been generated. mpv was not available in the development environment at the time Task 6 was completed.

Commands to generate reference screenshots (once mpv is available) #

# Ensure mpv with libass is installed (NixOS example)
nix-shell -p mpv

# Render a screenshot at 2 seconds (overlaps lines at 1s and 2s)
mpv --no-audio \
    --sub-file=tests/subtitle-reference/basic-styled.ass \
    --screenshot-format=png \
    --screenshot-directory=tests/subtitle-reference/reference/ \
    --start=2 --end=2.1 \
    --frames=1 \
    "tests/subtitle-reference/basic-styled.ass" \
    --vf="lavfi=[color=black:640x480:rate=1]" \
    --o="tests/subtitle-reference/reference/basic-styled-2s.png"

# Alternative: use ffmpeg with libass
ffmpeg -f lavfi -i "color=black:640x480:rate=1" \
    -vf "ass=tests/subtitle-reference/basic-styled.ass" \
    -vframes 1 -ss 2 \
    tests/subtitle-reference/reference/basic-styled-2s.png

ffmpeg -f lavfi -i "color=black:640x480:rate=1" \
    -vf "ass=tests/subtitle-reference/basic-styled.ass" \
    -vframes 1 -ss 3 \
    tests/subtitle-reference/reference/basic-styled-3s.png

ffmpeg -f lavfi -i "color=black:640x480:rate=1" \
    -vf "ass=tests/subtitle-reference/basic-styled.ass" \
    -vframes 1 -ss 10 \
    tests/subtitle-reference/reference/basic-styled-10s.png

Save outputs as:

tests/subtitle-reference/reference/basic-styled-2s.png — shows "Hello, world!" (default) + "Top text" (top)
tests/subtitle-reference/reference/basic-styled-3s.png — shows all three overlapping lines
tests/subtitle-reference/reference/basic-styled-10s.png — shows CJK text

Visual Validation Notes #

Pixel-perfect matching between ass-rs and mpv/libass is not expected and is not the bar. The two renderers use different rasterisation engines:

mpv uses libass (C library, FreeType-based rasterisation)
ass-rs uses rustybuzz + fontdb (Rust, HarfBuzz-compatible shaping)

The visual bar is: correct text, correct colour, correct position, correct inline tag application. Sub-pixel kerning differences, anti-aliasing differences, and minor layout variations are acceptable.

Pixel-exact regression testing is deferred to Phase 7, which will use a canvas toDataURL() capture against a stored baseline from the browser.

Subtitle Reference Test Files #

Files #

aegisub-format-tests.ass #

basic-styled.ass #

validation-results.md #

Reference Screenshots #

Commands to generate reference screenshots (once mpv is available) #

Visual Validation Notes #

`aegisub-format-tests.ass` #

`basic-styled.ass` #

`validation-results.md` #