refactor: abstraction for transcoding

go/cmd/particleprocessorworker/main.go

@@ -1,19 +1,18 @@
 package main
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"log"
 	"log/slog"
 	"os"
-	"os/exec"
 	"strings"
 	"time"
 
 	"github.com/flowy-live/llink/internal/billing"
 	"github.com/flowy-live/llink/internal/db"
 	"github.com/flowy-live/llink/internal/depot"
+	"github.com/flowy-live/llink/internal/media"
 	"github.com/flowy-live/llink/internal/particle"
 	"github.com/flowy-live/llink/internal/speech"
 	"github.com/flowy-live/llink/internal/utils"
@@ -106,6 +105,7 @@ func main() {
 			slog.Debug("processing particle", "particleID", particleID, "data", change.Doc.Data())
 
 			// --- Perform side effects ---
+			// All of them do not stop us from marking the particle as processed
 
 			updateParentLastChildCreatedAt(ctx, change.Doc)
 			transcribeMediaParticle(ctx, depotSvc, speechSvc, change.Doc)
@@ -187,7 +187,7 @@ func transcodeMediaParticle(ctx context.Context, depotSvc depot.Service, doc *fi
 		return
 	}
 	if particleType != particle.TypeMedia {
-    slog.Info("transcode: particle is not of type media")
+		slog.Info("transcode: particle is not of type media")
 		return
 	}
 
@@ -197,8 +197,8 @@ func transcodeMediaParticle(ctx context.Context, depotSvc depot.Service, doc *fi
 	}
 
 	// Source is already iOS-playable; nothing to do.
-	if isIOSPlayableMime(mediaParticle.Properties.MimeType) {
+	if media.IsIOSPlayableMime(mediaParticle.Properties.MimeType) {
-    slog.Info("transcode: skipping because already playable on ios")
+		slog.Info("transcode: skipping because already playable on ios")
 		return
 	}
 
@@ -208,81 +208,35 @@ func transcodeMediaParticle(ctx context.Context, depotSvc depot.Service, doc *fi
 		return
 	}
 
-	isAudio := strings.HasPrefix(mediaParticle.Properties.MimeType, "audio/")
-	var outputExt, outputMime string
-	if isAudio {
-		outputExt = ".m4a"
-		outputMime = "audio/mp4"
-	} else {
-		outputExt = ".mp4"
-		outputMime = "video/mp4"
-	}
-
-	tmp, err := os.CreateTemp("", "transcode-*"+outputExt)
-	if err != nil {
-		slog.Error("transcode: failed to create temp file", "error", err)
-		return
-	}
-	tmpPath := tmp.Name()
-	tmp.Close()
-	defer os.Remove(tmpPath)
-
-	transcodeCtx, cancel := context.WithTimeout(ctx, 5*time.Minute)
-	defer cancel()
-
-	var args []string
-	if isAudio {
-		args = []string{
-			"-y", "-i", sourceURL,
-			"-vn",
-			"-c:a", "aac", "-b:a", "128k",
-			"-movflags", "+faststart",
-			tmpPath,
-		}
-	} else {
-		// Cap encoder parallelism and lookahead to keep memory bounded — screen
-		// recordings come in at native display resolution (often 1440p–4K) and
-		// libx264's per-thread lookahead/reference buffers blow past the worker's
-		// memory limit otherwise. Output is also downscaled to 1080p max, which
-		// mobile playback won't notice; the original WebM stays in GCS untouched.
-		args = []string{
-			"-y", "-i", sourceURL,
-			"-vf", "scale='min(1920,iw)':-2:flags=lanczos",
-			"-c:v", "libx264", "-preset", "veryfast", "-crf", "23",
-			"-pix_fmt", "yuv420p", "-profile:v", "baseline", "-level", "3.1",
-			"-x264-params", "rc-lookahead=20:ref=2",
-			"-threads", "2", "-filter_threads", "2",
-			"-c:a", "aac", "-b:a", "128k",
-			"-movflags", "+faststart",
-			tmpPath,
-		}
-	}
-
-	cmd := exec.CommandContext(transcodeCtx, "ffmpeg", args...)
-	var stderr bytes.Buffer
-	cmd.Stderr = &stderr
-	if err := cmd.Run(); err != nil {
-		slog.Error("transcode: ffmpeg failed", "error", err, "stderr", stderr.String(), "particleID", doc.Ref.ID)
-		return
-	}
-
 	networkID, err := networkIDFromParticlePath(doc.Ref.Path)
 	if err != nil {
 		slog.Error("transcode: failed to derive network id", "error", err, "path", doc.Ref.Path)
 		return
 	}
 
-	f, err := os.Open(tmpPath)
+	transcodeCtx, cancel := context.WithTimeout(ctx, 5*time.Minute)
+	defer cancel()
+	transcodeOutput, err := media.TranscodeToMp4(transcodeCtx, media.TranscodeInput{
+		SourceURL: sourceURL,
+		MimeType:  mediaParticle.Properties.MimeType,
+	})
 	if err != nil {
-		slog.Error("transcode: failed to open transcoded file", "error", err, "path", tmpPath)
+		slog.Error("transcode: ffmpeg failed", "error", err)
+		return
+	}
+	defer os.Remove(transcodeOutput.TempLocalFilePath)
+
+	f, err := os.Open(transcodeOutput.TempLocalFilePath)
+	if err != nil {
+		slog.Error("transcode: failed to open transcoded file", "error", err, "path", transcodeOutput.TempLocalFilePath)
 		return
 	}
 	defer f.Close()
 
 	newObj, err := depotSvc.CreateFromReader(ctx, depot.CreateFromReaderInput{
 		Prefix:      networkID,
-		Name:        "transcoded" + outputExt,
+		Name:        "transcoded" + transcodeOutput.OutputExt,
-		ContentType: outputMime,
+		ContentType: transcodeOutput.OutputMimeType,
 	}, f)
 	if err != nil {
 		slog.Error("transcode: failed to upload transcoded object", "error", err, "particleID", doc.Ref.ID)
@@ -292,7 +246,7 @@ func transcodeMediaParticle(ctx context.Context, depotSvc depot.Service, doc *fi
 	_, err = doc.Ref.Set(ctx, map[string]interface{}{
 		"properties": map[string]interface{}{
 			"transcoded_object_id": newObj.ID,
-			"transcoded_mime_type": outputMime,
+			"transcoded_mime_type": transcodeOutput.OutputMimeType,
 		},
 	}, firestore.MergeAll)
 	if err != nil {
@@ -300,15 +254,7 @@ func transcodeMediaParticle(ctx context.Context, depotSvc depot.Service, doc *fi
 		return
 	}
 
-	slog.Info("transcoded media particle", "particleID", doc.Ref.ID, "transcoded_object_id", newObj.ID, "mime", outputMime)
+	slog.Info("transcoded media particle", "particleID", doc.Ref.ID, "transcoded_object_id", newObj.ID, "mime", transcodeOutput.OutputMimeType)
-}
-
-func isIOSPlayableMime(mime string) bool {
-	switch mime {
-	case "video/mp4", "video/quicktime", "audio/mp4", "audio/aac", "audio/x-m4a", "audio/mpeg":
-		return true
-	}
-	return false
 }
 
 func toFirestoreTranscript(result *speech.TranscriptResult) particle.FirestoreTranscript {

go/internal/media/helpers.go

@@ -0,0 +1,107 @@
+package media
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"log/slog"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+func IsIOSPlayableMime(mime string) bool {
+	switch mime {
+	case "video/mp4", "video/quicktime", "audio/mp4", "audio/aac", "audio/x-m4a", "audio/mpeg":
+		return true
+	}
+	return false
+}
+
+func IsAudio(mime string) bool {
+	return strings.HasPrefix(mime, "audio/")
+}
+
+type TranscodeInput struct {
+	SourceURL string
+	MimeType  string
+}
+
+type TranscodeOutput struct {
+	TempLocalFilePath string
+	OutputMimeType    string
+	// Extension such as ".m4a" or ".mp4"
+	OutputExt string
+}
+
+var (
+	ErrInvalidInput error = errors.New("invalid input")
+)
+
+// TranscodeToMp4 takes in any audio or video source URL and
+// returns the filepath of the transcoded media
+// WARNING: caller responsible for deleting TempLocalFilePath
+func TranscodeToMp4(ctx context.Context, input TranscodeInput) (*TranscodeOutput, error) {
+	if input.SourceURL == "" || input.MimeType == "" {
+		return nil, ErrInvalidInput
+	}
+
+	isAudio := IsAudio(input.MimeType)
+	var outputExt, outputMime string
+	if isAudio {
+		outputExt = ".m4a"
+		outputMime = "audio/mp4"
+	} else {
+		outputExt = ".mp4"
+		outputMime = "video/mp4"
+	}
+
+	tmp, err := os.CreateTemp("", "transcode-*"+outputExt)
+	if err != nil {
+		slog.Error("transcode: failed to create temp file", "error", err)
+		return nil, err
+	}
+	tmpPath := tmp.Name()
+	tmp.Close()
+
+	var args []string
+	if isAudio {
+		args = []string{
+			"-y", "-i", input.SourceURL,
+			"-vn",
+			"-c:a", "aac", "-b:a", "128k",
+			"-movflags", "+faststart",
+			tmpPath,
+		}
+	} else {
+		// Cap encoder parallelism and lookahead to keep memory bounded — screen
+		// recordings come in at native display resolution (often 1440p–4K) and
+		// libx264's per-thread lookahead/reference buffers blow past the worker's
+		// memory limit otherwise. Output is also downscaled to 1080p max, which
+		// mobile playback won't notice; the original WebM stays in GCS untouched.
+		args = []string{
+			"-y", "-i", input.SourceURL,
+			"-vf", "scale='min(1920,iw)':-2:flags=lanczos",
+			"-c:v", "libx264", "-preset", "veryfast", "-crf", "23",
+			"-pix_fmt", "yuv420p", "-profile:v", "baseline", "-level", "3.1",
+			"-x264-params", "rc-lookahead=20:ref=2",
+			"-threads", "2", "-filter_threads", "2",
+			"-c:a", "aac", "-b:a", "128k",
+			"-movflags", "+faststart",
+			tmpPath,
+		}
+	}
+
+	cmd := exec.CommandContext(ctx, "ffmpeg", args...)
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		return nil, errors.Join(err, errors.New(stderr.String()))
+	}
+
+	return &TranscodeOutput{
+		TempLocalFilePath: tmpPath,
+		OutputMimeType:    outputMime,
+		OutputExt:         outputExt,
+	}, nil
+}