fix(v2): log redacted ffmpeg/ffprobe stderr on stream failure

The stream worker discarded ffmpeg stderr, so reconnect loops were opaque.
Capture stderr and log it with the RTSP URL/credentials redacted, so the
real cause (auth, timeout, option, URL parse) is diagnosable without
leaking the source address.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

v2/internal/source/stream.go

@@ -2,18 +2,32 @@
 package source
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
+	"log"
 	"os/exec"
+	"regexp"
 	"strconv"
 	"strings"
 	"sync"
 	"time"
 )
 
+var rtspURLPattern = regexp.MustCompile(`rtsp://[^\s'"]+`)
+
+// redact removes the resolved source URL (which may carry credentials) from any
+// FFmpeg/FFprobe diagnostic text before it is logged.
+func redact(text, sourceURL string) string {
+	if sourceURL != "" {
+		text = strings.ReplaceAll(text, sourceURL, "<source>")
+	}
+	return rtspURLPattern.ReplaceAllString(text, "rtsp://<redacted>")
+}
+
 type Status string
 
 const (
@@ -195,8 +209,12 @@ func probe(ctx context.Context, config Config) (Metadata, error) {
 	args := []string{"-v", "error", "-select_streams", "v:0", "-show_entries", "stream=width,height,r_frame_rate", "-of", "json"}
 	args = appendInputOptions(args, config)
 	args = append(args, "-i", config.SourceURL)
-	output, err := exec.CommandContext(ctx, config.FFprobePath, args...).Output()
+	command := exec.CommandContext(ctx, config.FFprobePath, args...)
+	var stderr bytes.Buffer
+	command.Stderr = &stderr
+	output, err := command.Output()
 	if err != nil {
+		log.Printf("ffprobe 探测失败：%s（%v）", strings.TrimSpace(redact(stderr.String(), config.SourceURL)), err)
 		return Metadata{}, errors.New("unable to probe video metadata")
 	}
 	var parsed struct {
@@ -230,7 +248,8 @@ func decode(ctx context.Context, config Config, metadata Metadata, publish func(
 	args := append([]string{"-hide_banner", "-loglevel", "error"}, appendInputOptions(nil, config)...)
 	args = append(args, "-i", config.SourceURL, "-an", "-sn", "-dn", "-f", "rawvideo", "-pix_fmt", "bgr24", "-")
 	command := exec.CommandContext(ctx, config.FFmpegPath, args...)
-	command.Stderr = io.Discard
+	var stderr bytes.Buffer
+	command.Stderr = &stderr
 	stdout, err := command.StdoutPipe()
 	if err != nil {
 		return errors.New("unable to read video frames")
@@ -247,6 +266,7 @@ func decode(ctx context.Context, config Config, metadata Metadata, publish func(
 			if ctx.Err() != nil {
 				return ctx.Err()
 			}
+			log.Printf("ffmpeg 解码停止：%s（%v）", strings.TrimSpace(redact(stderr.String(), config.SourceURL)), err)
 			return errors.New("video decoder stopped")
 		}
 		publish(frame)