Function v4l2_available 

pub fn v4l2_available() -> bool

Returns true when a V4L2 memory-to-memory JPEG decoder (e.g. the i.MX mxc-jpeg block) is present and not opted out via EDGEFIRST_DISABLE_V4L2. Opens and drops the device once; the decode path re-probes lazily and keeps its own context. Always false on other platforms or when the v4l2 feature is disabled. Useful for benchmarks and consumers that must fail fast instead of silently falling back to the CPU decoder.