feat: Support multiple input formats w/ ffmpeg#7
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Overview
Today the server only accepts WAV uploads. Anything else (MP3, OGG, WebM, FLAC, M4A, AAC, Opus, ...) is rejected with a
"not yet implemented" error, which is awkward for a Whisper-compatible API since most OpenAI clients upload compressed audio by default.
This PR adds an optional ffmpeg-backed fallback: if the upload is not a WAV, the server transcodes it to 16 kHz mono WAV
on the fly and then runs the normal pipeline. Format is detected by reading the file's magic bytes, not the filename, so
clients that upload without an extension still work.
How it works
• WAV input is still parsed in pure Go — no external process involved. That is the fast path.
• Non-WAV input is handed to a small ffmpegConverter that shells out to the system ffmpeg binary with a timeout and
captured stderr.
• At startup we run a single exec.LookPath("ffmpeg") . If ffmpeg is not installed, conversion is disabled cleanly: the
server boots, logs a warning, and any non-WAV upload gets a clear 400 invalid_request_error instead of a 500.
• Each conversion uses os.CreateTemp for input and output files, so concurrent requests never share paths. This keeps
the guarantees of the existing worker pool intact.