0.2.69 - Homepage loading improvements pass

server/internal/credits/sampler.go

@@ -122,21 +122,51 @@ func (s *Sampler) Sample(
 	ctx, cancel := context.WithTimeout(ctx, timeout)
 	defer cancel()
 
+	stats, err := s.samplePass(ctx, url, from, to, interval, false)
+	if err == nil || !decoderCrashed(err) || ctx.Err() != nil {
+		return stats, err
+	}
+	// A decoder crash is local to the ffmpeg process, not evidence that the media is
+	// unreadable. Retry once with conservative decoder settings: single-threaded decoding
+	// avoids the most common native-code race, while corrupt packets are discarded rather
+	// than handed back through the failing path. Ordinary HTTP and authentication failures
+	// are never retried here.
+	stats, retryErr := s.samplePass(ctx, url, from, to, interval, true)
+	if retryErr != nil {
+		return stats, fmt.Errorf("credits: conservative ffmpeg retry: %w", retryErr)
+	}
+	return stats, nil
+}
+
+func (s *Sampler) samplePass(
+	ctx context.Context, url string, from, to time.Duration, interval time.Duration,
+	conservative bool,
+) ([]frameStats, error) {
+
 	// -ss ahead of -i is the whole optimisation: it seeks in the container before opening a
 	// decoder, so the input starts near the credits. Behind -i it would decode from zero and
 	// discard, which is the full read this package exists to avoid.
 	args := []string{
 		"-hide_banner", "-loglevel", "error", "-nostdin",
 		"-ss", formatSeconds(from),
+	}
+	if conservative {
+		args = append(args,
+			"-threads", "1",
+			"-fflags", "+discardcorrupt",
+			"-err_detect", "ignore_err",
+		)
+	}
+	args = append(args,
 		"-i", url,
-		"-t", formatSeconds(to - from),
+		"-t", formatSeconds(to-from),
 		"-an", "-sn", "-dn",
 		"-vf", fmt.Sprintf("fps=%s,scale=%d:%d,format=gray",
 			formatRate(interval), sampleWidth, sampleHeight),
 		"-frames:v", strconv.Itoa(maxFrames),
 		"-f", "rawvideo", "-pix_fmt", "gray",
 		"pipe:1",
-	}
+	)
 
 	cmd := exec.CommandContext(ctx, s.binary(), args...)
 	// Cancel and WaitDelay together are what stop an orphan. CommandContext's default is to
@@ -181,6 +211,24 @@ func (s *Sampler) Sample(
 	return stats, nil
 }
 
+func decoderCrashed(err error) bool {
+	if err == nil {
+		return false
+	}
+	message := strings.ToLower(err.Error())
+	for _, signature := range []string{
+		"segmentation fault",
+		"signal: aborted",
+		"signal: bus error",
+		"access violation",
+	} {
+		if strings.Contains(message, signature) {
+			return true
+		}
+	}
+	return false
+}
+
 // readFrames pulls fixed-size grayscale frames off the pipe and reduces each one as it
 // arrives. The frame buffer is allocated once and reused, so a four-hundred-frame pass
 // allocates fourteen kilobytes rather than five and a half megabytes.