Ettore Di Giacinto a996d7dd23 backend(audio-cpp): serve the TTSStream and AudioTranscriptionStream RPCs ...

TTSStream leads with a streaming WAV header carrying 0xFFFFFFFF sizes, matching
the convention backend/go/vibevoice-cpp established, so an HTTP client can start
playback before the full PCM exists. Its chunks are read from
StreamEvent::named_audio_outputs and not audio_output: supertonic, omnivoice and
voxcpm2 all put their streamed audio there and leave audio_output empty until
the very end, so reading the obvious field yields a stream with no audio in it.
The finish_stream result is the family's own merged whole rather than a tail, so
it is emitted only when nothing was streamed.

Streaming transcription sends incremental deltas and degrades to a single delta
plus the final result on families that offer no streaming ASR, which is the same
message sequence with fewer deltas. The four streaming ASR families disagree on
what partial_text means: nemotron_asr, vibevoice_asr and higgs_audio_stt report
incremental fragments while voxtral_realtime reports the whole hypothesis and
reports it twice, so the reconciliation lives in one tested unit rather than in
the handler. nemotron_asr reports only through the stream event sink, and only
from inside finalize, so the audio driver installs one and clears it again
before returning: the session is cached and a sink left holding the caller's
frame is a use after free waiting for the next stream.

begin_stream is now the only implementation of the streaming state obligation,
prepare then start_stream. Streaming sessions are cached, and what clears the
previous stream is start_stream's reset; a family override that dropped it would
break every call site with no compile error, so there is one call site.

Assisted-by: Claude:claude-opus-5 [Claude Code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

2026-07-29 19:03:33 +00:00

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