feat: generate transcript and event-driven particle processing

This generates the transcript and shows the caption experience on the
client side for media particles. It also simplifies other side effects
that we must perform such as updating the `last_child_created_at` field
for stream and container particles.

go/internal/speech/service.go

@@ -0,0 +1,99 @@
+package speech
+
+import (
+	"context"
+	"log/slog"
+
+	dgapi "github.com/deepgram/deepgram-go-sdk/v3/pkg/api/listen/v1/rest"
+	interfaces "github.com/deepgram/deepgram-go-sdk/v3/pkg/client/interfaces"
+	client "github.com/deepgram/deepgram-go-sdk/v3/pkg/client/listen"
+)
+
+type TranscriptWord struct {
+	Word  string
+	Start float64
+	End   float64
+}
+
+type TranscriptSentence struct {
+	Text  string
+	Start float64
+	End   float64
+}
+
+type TranscriptParagraph struct {
+	Sentences []TranscriptSentence
+	Start     float64
+	End       float64
+}
+
+type TranscriptResult struct {
+	Transcript string
+	Words      []TranscriptWord
+	Paragraphs []TranscriptParagraph
+}
+
+type SpeechService interface {
+	Transcribe(ctx context.Context, mediaUrl string) (*TranscriptResult, error)
+}
+
+type speechServiceImpl struct {
+	deepgramClient *dgapi.Client
+}
+
+func NewSpeechService(ctx context.Context) SpeechService {
+	return &speechServiceImpl{
+		deepgramClient: dgapi.New(client.NewRESTWithDefaults()),
+	}
+}
+
+func (s *speechServiceImpl) Transcribe(ctx context.Context, mediaUrl string) (*TranscriptResult, error) {
+	options := &interfaces.PreRecordedTranscriptionOptions{
+		Model:      "nova-3",
+		SmartFormat: true,
+		Paragraphs: true,
+	}
+
+	response, err := s.deepgramClient.FromURL(ctx, mediaUrl, options)
+	if err != nil {
+		slog.Error("failed to transcribe prerecorded media", "error", err)
+		return nil, err
+	}
+
+	alt := response.Results.Channels[0].Alternatives[0]
+
+	words := make([]TranscriptWord, len(alt.Words))
+	for i, w := range alt.Words {
+		words[i] = TranscriptWord{
+			Word:  w.PunctuatedWord,
+			Start: w.Start,
+			End:   w.End,
+		}
+	}
+
+	var paragraphs []TranscriptParagraph
+	if alt.Paragraphs != nil {
+		paragraphs = make([]TranscriptParagraph, len(alt.Paragraphs.Paragraphs))
+		for i, p := range alt.Paragraphs.Paragraphs {
+			sentences := make([]TranscriptSentence, len(p.Sentences))
+			for j, s := range p.Sentences {
+				sentences[j] = TranscriptSentence{
+					Text:  s.Text,
+					Start: s.Start,
+					End:   s.End,
+				}
+			}
+			paragraphs[i] = TranscriptParagraph{
+				Sentences: sentences,
+				Start:     p.Start,
+				End:       p.End,
+			}
+		}
+	}
+
+	return &TranscriptResult{
+		Transcript: alt.Transcript,
+		Words:      words,
+		Paragraphs: paragraphs,
+	}, nil
+}