From 8759a6613eb425384798d6203d0e3294cc494aec Mon Sep 17 00:00:00 2001
From: Domagoj Zecevic <domagoj@zecevic-ninja.com>
Date: Fri, 19 Jun 2026 11:01:49 +0200
Subject: [PATCH] create thumbs bug

---
 internal/video/thumb.go | 42 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 7 deletions(-)

diff --git a/internal/video/thumb.go b/internal/video/thumb.go
index dc2c16b..f810a85 100644
--- a/internal/video/thumb.go
+++ b/internal/video/thumb.go
@@ -2,9 +2,13 @@ package video
 
 import (
 	"bytes"
+	"context"
 	"fmt"
+	"log"
 	"os/exec"
+	"path/filepath"
 	"sync"
+	"time"
 )
 
 const (
@@ -36,20 +40,32 @@ func NewCache(max int, ffmpegPath string) *Cache {
 	}
 }
 
+// thumbnailTimeout is the maximum time we allow ffmpeg to spend extracting
+// a single frame.  Most clips produce a frame in under a second; 30 s is a
+// generous safety net for slow hardware or unexpectedly large files.
+const thumbnailTimeout = 30 * time.Second
+
 func (c *Cache) Thumbnail(absPath string) ([]byte, error) {
 	if cached, ok := c.get(absPath); ok {
 		return cached, nil
 	}
 
-	cmd := exec.Command(
+	ctx, cancel := context.WithTimeout(context.Background(), thumbnailTimeout)
+	defer cancel()
+
+	cmd := exec.CommandContext(
+		ctx,
 		c.ffmpegPath,
 		"-loglevel", "error",
 		"-i", absPath,
-		// -ss must come AFTER -i for raw H.265 bitstreams.
-		// Input seeking (-ss before -i) requires an index that raw streams lack,
-		// causing "could not seek to position 0.000" and an empty output.
-		// Output seeking (-ss after -i) decodes from the start and is reliable.
-		"-ss", "0",
+		// Do NOT use -ss here.
+		// -ss before -i: input seeking — raw H.265 has no index, causes
+		//   "could not seek to position 0.000" and empty output.
+		// -ss after  -i: output seeking — decodes from start then skips,
+		//   still trips on files whose first NAL units are invalid.
+		// Dropping -ss entirely and using only -vframes 1 lets ffmpeg decode
+		// until it finds the first valid frame, which is robust across all
+		// camera files regardless of their NAL unit layout.
 		"-vframes", "1",
 		"-vf", fmt.Sprintf("scale=%d:%d:force_original_aspect_ratio=decrease", thumbnailWidth, thumbnailHeight),
 		"-f", "image2",
@@ -62,7 +78,19 @@ func (c *Cache) Thumbnail(absPath string) ([]byte, error) {
 
 	output, err := cmd.Output()
 	if err != nil {
-		return nil, fmt.Errorf("generate video thumbnail: %w%s", err, stderrSuffix(stderr.String()))
+		log.Printf("video thumbnail failed for %s: %v — stderr: %s",
+			filepath.Base(absPath), err, stderr.String())
+		return nil, fmt.Errorf("generate video thumbnail: %w", err)
+	}
+
+	// ffmpeg can exit 0 but write nothing when the file has no decodable
+	// frame (truncated clip, all-invalid NAL units, etc.).  Treat empty
+	// output as an error so we never cache broken placeholder bytes and
+	// serve them as a "successful" thumbnail on every subsequent request.
+	if len(output) == 0 {
+		log.Printf("video thumbnail: empty output for %s — stderr: %s",
+			filepath.Base(absPath), stderr.String())
+		return nil, fmt.Errorf("video thumbnail: no frame decoded from %s", filepath.Base(absPath))
 	}
 
 	c.add(absPath, output)