Marp Processor

Purpose

Converts Markdown slides to PDF, PPTX, or HTML using Marp.

How It Works

Discovers .md files in the project and runs marp on each file, generating output in the configured formats. Each format produces a separate output file.

Each marp invocation spawns a headless Chromium browser instance via Puppeteer to render the slides. This makes marp significantly more resource-intensive than typical processors — see Concurrency limiting below.

Source Files

• Input: **/*.md
• Output: out/marp/{format}/{relative_path}.{format}

Configuration

[processor.marp]
marp_bin = "marp"                      # The marp command to run
formats = ["pdf"]                      # Output formats (pdf, pptx, html)
args = ["--html", "--allow-local-files"]  # Additional arguments to pass to marp
output_dir = "out/marp"                # Output directory
dep_inputs = []                      # Additional files that trigger rebuilds when changed
max_jobs = 2                           # Limit concurrent marp instances (each spawns Chromium)

Concurrency Limiting

Each marp invocation launches a full headless Chromium browser process, which consumes hundreds of megabytes of RAM. When running parallel builds with -j N, too many simultaneous Chromium instances cause resource exhaustion and non-deterministic crashes:

TargetCloseError: Protocol error (Target.setDiscoverTargets): Target closed

Use max_jobs to limit how many marp processes run concurrently, independent of the global -j setting. For example, with -j 20 and max_jobs = 2, at most 2 Chromium instances will be alive at once while other processors still use the full 20 threads:

[processor.marp]
formats = ["pdf"]
max_jobs = 2

Recommended value: 2. A value of 4 may work on machines with plenty of RAM but has been observed to produce occasional failures on large projects (700+ slides). Without max_jobs, the global -j value applies, which typically causes crashes at higher parallelism levels.

Batch Support

Each input file is processed individually, producing its own output file.

Temporary Files

Marp creates temporary Chromium profile directories (marp-cli-*) in /tmp for each invocation. RSConstruct automatically cleans these up after each marp process completes, since marp itself does not delete them.