formatHint

The demuxer to open the item with, by FFmpeg name, for example "mpegts" or "s16le". Almost never needed: probing is reliable.

The FFmpeg backend forces this demuxer, as the command line's -f does, so the open does not probe. That opens input with nothing to probe, such as raw PCM, whose parameters go in openOptions (sample_rate, ch_layout). Bytes that are not that format fail the open, and a name the build does not carry fails it too.