diff --git a/.gitignore b/.gitignore
index 579b3e2..f4637d5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 /lerobot-go
+/bin/
 /go-lerobot
 /lerobot-ds
 *.test
diff --git a/internal/v21/integrity.go b/internal/v21/integrity.go
new file mode 100644
index 0000000..c4f36f2
--- /dev/null
+++ b/internal/v21/integrity.go
@@ -0,0 +1,100 @@
+package v21
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/ioai-tech/lerobot-go/internal/meta"
+)
+
+func requiredVideoKeys(features map[string]meta.FeatureSpec) []string {
+	var keys []string
+	for k, f := range features {
+		if f.DType == "video" {
+			keys = append(keys, k)
+		}
+	}
+	return keys
+}
+
+// ValidateOutputIntegrity checks merged v2.1 dataset has per-episode parquet and video files.
+func ValidateOutputIntegrity(outputRoot string, info meta.DatasetInfo, features map[string]meta.FeatureSpec) error {
+	if info.TotalEpisodes <= 0 {
+		matches, err := filepath.Glob(filepath.Join(outputRoot, meta.DataDir, "*", "episode_*.parquet"))
+		if err != nil {
+			return err
+		}
+		if len(matches) == 0 {
+			matches, err = filepath.Glob(filepath.Join(outputRoot, meta.DataDir, "*", "*.parquet"))
+			if err != nil {
+				return err
+			}
+		}
+		if len(matches) == 0 {
+			return fmt.Errorf("no v2.1 data parquet files under %s", outputRoot)
+		}
+		for _, p := range matches {
+			if err := nonEmptyFile(p); err != nil {
+				return err
+			}
+		}
+	} else {
+		for ep := 0; ep < info.TotalEpisodes; ep++ {
+			p := filepath.Join(outputRoot, meta.V21DataPathFromInfo(info, ep))
+			if err := nonEmptyFile(p); err != nil {
+				return fmt.Errorf("episode %d: %w", ep, err)
+			}
+		}
+	}
+	if !hasVideoFeatures(features) {
+		return nil
+	}
+	for _, vk := range requiredVideoKeys(features) {
+		found := 0
+		for ep := 0; ep < max(1, info.TotalEpisodes); ep++ {
+			p := filepath.Join(outputRoot, meta.V21VideoPathFromInfo(info, vk, ep))
+			if err := nonEmptyFile(p); err == nil {
+				found++
+				continue
+			}
+			alt := filepath.Join(outputRoot, meta.V21VideoPathFromInfo(info, filepath.Base(vk), ep))
+			if err := nonEmptyFile(alt); err == nil {
+				found++
+			}
+		}
+		if found == 0 {
+			glob, _ := filepath.Glob(filepath.Join(outputRoot, "videos", "*", vk, "episode_*.mp4"))
+			if len(glob) == 0 {
+				glob, _ = filepath.Glob(filepath.Join(outputRoot, "videos", "*", filepath.Base(vk), "episode_*.mp4"))
+			}
+			if len(glob) == 0 {
+				return fmt.Errorf("no merged video files for feature %q", vk)
+			}
+			for _, f := range glob {
+				if err := nonEmptyFile(f); err != nil {
+					return err
+				}
+			}
+		}
+	}
+	return nil
+}
+
+func nonEmptyFile(path string) error {
+	fi, err := os.Stat(path)
+	if err != nil {
+		return fmt.Errorf("file missing %s: %w", path, err)
+	}
+	if fi.Size() == 0 {
+		return fmt.Errorf("file empty: %s", path)
+	}
+	return nil
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
diff --git a/internal/v21/integrity_test.go b/internal/v21/integrity_test.go
new file mode 100644
index 0000000..4d356a3
--- /dev/null
+++ b/internal/v21/integrity_test.go
@@ -0,0 +1,68 @@
+package v21
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/ioai-tech/lerobot-go/internal/meta"
+)
+
+func TestValidateOutputIntegrityParquetOK(t *testing.T) {
+	root := t.TempDir()
+	info := meta.NewDatasetInfo(meta.CodebaseV21, 30, map[string]meta.FeatureSpec{
+		"observation.state": {DType: "float32", Shape: []int{2}},
+	}, false, "test")
+	info.TotalEpisodes = 1
+	pq := filepath.Join(root, meta.V21DataPathFromInfo(info, 0))
+	if err := os.MkdirAll(filepath.Dir(pq), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(pq, []byte("par1"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := ValidateOutputIntegrity(root, info, info.Features); err != nil {
+		t.Fatalf("expected ok: %v", err)
+	}
+}
+
+func TestValidateOutputIntegrityMissingParquet(t *testing.T) {
+	root := t.TempDir()
+	info := meta.NewDatasetInfo(meta.CodebaseV21, 30, map[string]meta.FeatureSpec{
+		"observation.state": {DType: "float32", Shape: []int{2}},
+	}, false, "test")
+	info.TotalEpisodes = 1
+	if err := ValidateOutputIntegrity(root, info, info.Features); err == nil {
+		t.Fatal("expected error for missing parquet")
+	}
+}
+
+func TestValidateOutputIntegrityVideoRequired(t *testing.T) {
+	root := t.TempDir()
+	features := map[string]meta.FeatureSpec{
+		"observation.state":              {DType: "float32", Shape: []int{2}},
+		"observation.images.cam":         {DType: "video", Shape: []int{4, 4, 3}},
+	}
+	info := meta.NewDatasetInfo(meta.CodebaseV21, 30, features, true, "test")
+	info.TotalEpisodes = 1
+	pq := filepath.Join(root, meta.V21DataPathFromInfo(info, 0))
+	if err := os.MkdirAll(filepath.Dir(pq), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(pq, []byte("par1"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := ValidateOutputIntegrity(root, info, features); err == nil {
+		t.Fatal("expected error for missing video")
+	}
+	vid := filepath.Join(root, meta.V21VideoPathFromInfo(info, "observation.images.cam", 0))
+	if err := os.MkdirAll(filepath.Dir(vid), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(vid, []byte("mp4"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := ValidateOutputIntegrity(root, info, features); err != nil {
+		t.Fatalf("expected ok with video: %v", err)
+	}
+}
diff --git a/internal/v21/merge.go b/internal/v21/merge.go
index 9cea32d..4ecf3f0 100644
--- a/internal/v21/merge.go
+++ b/internal/v21/merge.go
@@ -113,7 +113,13 @@ func Merge(ctx context.Context, cfg MergeConfig) error {
 	if err := meta.UpdateVideoFeaturesInfo(ctx, &info, cfg.OutputRoot, cfg.Locator); err != nil {
 		return err
 	}
-	return meta.WriteInfo(cfg.OutputRoot, info)
+	if err := meta.WriteInfo(cfg.OutputRoot, info); err != nil {
+		return err
+	}
+	if err := ValidateOutputIntegrity(cfg.OutputRoot, info, cfg.Features); err != nil {
+		return fmt.Errorf("merged output integrity: %w", err)
+	}
+	return nil
 }
 
 func copyFile(src, dst string) error {
diff --git a/internal/v21/staging.go b/internal/v21/staging.go
index 2a695b3..6760d14 100644
--- a/internal/v21/staging.go
+++ b/internal/v21/staging.go
@@ -277,7 +277,14 @@ func (w *StagingWriter) finalizeVideos(ctx context.Context) (map[string]string,
 		return videos, durations, nil
 	}
 	if w.cfg.H264Remux {
-		return w.finalizeH264RemuxVideos(ctx)
+		remuxVideos, remuxDurations, err := w.finalizeH264RemuxVideos(ctx)
+		if err != nil {
+			return nil, nil, err
+		}
+		if len(remuxVideos) > 0 {
+			return remuxVideos, remuxDurations, nil
+		}
+		// Decode-fallback path may have streamed RGB into per-episode encoders without SetH264Remux.
 	}
 	type encClose struct {
 		key string
diff --git a/internal/v21/staging_h264_fallback_test.go b/internal/v21/staging_h264_fallback_test.go
new file mode 100644
index 0000000..1d20e02
--- /dev/null
+++ b/internal/v21/staging_h264_fallback_test.go
@@ -0,0 +1,65 @@
+package v21
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+
+	"github.com/ioai-tech/lerobot-go/internal/manifest"
+	"github.com/ioai-tech/lerobot-go/internal/meta"
+	"github.com/ioai-tech/lerobot-go/internal/video"
+)
+
+func TestStagingH264DecodeFallbackPopulatesVideos(t *testing.T) {
+	if _, err := exec.LookPath("ffmpeg"); err != nil {
+		t.Skip("ffmpeg not installed")
+	}
+	dir := t.TempDir()
+	key := "observation.images.cam"
+	w, err := NewStagingWriter(StagingConfig{
+		Dir:       dir,
+		Episode:   0,
+		FPS:       10,
+		UseVideos: true,
+		H264Remux: true,
+		Features: map[string]meta.FeatureSpec{
+			key: {DType: "video", Shape: []int{4, 4, 3}},
+		},
+	})
+	if err != nil {
+		t.Fatalf("NewStagingWriter: %v", err)
+	}
+	frame := video.VideoFrameRGB24{
+		Width: 4, Height: 4,
+		Data: make([]byte, 4*4*3),
+	}
+	for i := 0; i < 3; i++ {
+		if err := w.AppendRGBVideoFrame(context.Background(), key, frame); err != nil {
+			t.Fatalf("AppendRGBVideoFrame: %v", err)
+		}
+		if err := w.AddFrame(context.Background(), map[string]any{"task": "t"}); err != nil {
+			t.Fatalf("AddFrame: %v", err)
+		}
+	}
+	ep, err := w.SaveEpisode(context.Background())
+	if err != nil {
+		t.Fatalf("SaveEpisode: %v", err)
+	}
+	if len(ep.Videos) == 0 || ep.Videos[key] == "" {
+		t.Fatalf("expected videos map entry, got %#v", ep.Videos)
+	}
+	out := manifest.StagingMediaPath(dir, ep.Videos[key])
+	fi, err := os.Stat(out)
+	if err != nil {
+		t.Fatalf("missing staged mp4: %v", err)
+	}
+	if fi.Size() == 0 {
+		t.Fatal("empty staged mp4")
+	}
+	rel := filepath.Base(out)
+	if rel != "observation.images.cam.mp4" {
+		t.Fatalf("unexpected video rel basename: %s", rel)
+	}
+}
diff --git a/lerobot/writer.go b/lerobot/writer.go
index 10a3ae5..1eba41b 100644
--- a/lerobot/writer.go
+++ b/lerobot/writer.go
@@ -6,6 +6,7 @@ import (
 	"os"
 
 	"github.com/ioai-tech/lerobot-go/internal/manifest"
+	"github.com/ioai-tech/lerobot-go/internal/meta"
 	v21 "github.com/ioai-tech/lerobot-go/internal/v21"
 	v30 "github.com/ioai-tech/lerobot-go/internal/v30"
 	"github.com/ioai-tech/lerobot-go/internal/video"
@@ -201,7 +202,16 @@ func (d *serialDataset) Root() string { return d.root }
 
 // ValidateOutputIntegrity checks merged dataset has data parquet and video files.
 func ValidateOutputIntegrity(root string, features map[string]FeatureSpec) error {
-	return v30.ValidateOutputIntegrity(root, features)
+	info, err := meta.LoadInfo(root)
+	if err != nil {
+		return v30.ValidateOutputIntegrity(root, features)
+	}
+	switch info.CodebaseVersion {
+	case meta.CodebaseV21:
+		return v21.ValidateOutputIntegrity(root, info, features)
+	default:
+		return v30.ValidateOutputIntegrity(root, features)
+	}
 }
 
 // Merge finalizes completed staging episodes into the official on-disk layout.