fix Start stream 3 seconds behind edge

2026-06-27 15:44:56 +02:00
parent f715130302
commit 7c81ef94ca
5 changed files with 105 additions and 3 deletions
@@ -71,8 +71,9 @@ public interface IStreamProxyService
    /// <param name="manifestContent">The variant manifest content.</param>
    /// <param name="baseProxyUrl">The base proxy URL (without query params).</param>
    /// <param name="queryParams">Query parameters to append to rewritten URLs (e.g., "?token=abc").</param>
+    /// <param name="isLiveStream">Whether this is a livestream; if so an EXT-X-START offset is injected.</param>
    /// <returns>The rewritten manifest content.</returns>
-    string RewriteVariantManifestUrls(string manifestContent, string baseProxyUrl, string queryParams);
+    string RewriteVariantManifestUrls(string manifestContent, string baseProxyUrl, string queryParams, bool isLiveStream = false);

    /// <summary>
    /// Cleans up old and expired stream mappings.
@@ -900,9 +900,15 @@ public class StreamProxyService : IStreamProxyService
    /// <param name="manifestContent">The variant manifest content.</param>
    /// <param name="baseProxyUrl">The base proxy URL (without query params).</param>
    /// <param name="queryParams">Query parameters to append to rewritten URLs (e.g., "?token=abc").</param>
+    /// <param name="isLiveStream">Whether this is a livestream; if so an EXT-X-START offset is injected.</param>
    /// <returns>The rewritten manifest content.</returns>
-    public string RewriteVariantManifestUrls(string manifestContent, string baseProxyUrl, string queryParams)
+    public string RewriteVariantManifestUrls(string manifestContent, string baseProxyUrl, string queryParams, bool isLiveStream = false)
    {
+        if (isLiveStream)
+        {
+            manifestContent = InjectLiveStartOffset(manifestContent);
+        }
+
        string RewriteUrl(string url)
        {
            if (url.Contains("://", StringComparison.Ordinal))
@@ -953,6 +959,82 @@ public class StreamProxyService : IStreamProxyService
        return result.ToString();
    }

+    /// <summary>
+    /// Injects an <c>#EXT-X-START:TIME-OFFSET</c> tag into a live media playlist so that players
+    /// (notably ExoPlayer on Android TV) begin a few segments back from the volatile live edge
+    /// instead of at the edge itself, which otherwise causes stalling/jumping until a manual skip.
+    /// The offset is sized relative to the playlist's own <c>EXT-X-TARGETDURATION</c> to stay
+    /// RFC 8216 compliant (≥ 3 target durations from the edge for live playlists).
+    /// </summary>
+    /// <param name="manifestContent">The media playlist content.</param>
+    /// <returns>The playlist with the tag injected, or unchanged if it is not applicable.</returns>
+    private string InjectLiveStartOffset(string manifestContent)
+    {
+        var segmentsBack = Plugin.Instance?.Configuration?.LiveStartSegmentsBack ?? 3;
+        if (segmentsBack <= 0)
+        {
+            return manifestContent; // Disabled by config.
+        }
+
+        // Only a media playlist (has segments, no variant list) should carry EXT-X-START.
+        // A master/multivariant playlist or a VOD playlist (#EXT-X-ENDLIST) is left untouched.
+        if (!manifestContent.Contains("#EXTINF", StringComparison.Ordinal)
+            || manifestContent.Contains("#EXT-X-STREAM-INF", StringComparison.Ordinal)
+            || manifestContent.Contains("#EXT-X-ENDLIST", StringComparison.Ordinal))
+        {
+            return manifestContent;
+        }
+
+        // Don't add a second tag if the source already specified a start point.
+        if (manifestContent.Contains("#EXT-X-START", StringComparison.Ordinal))
+        {
+            _logger.LogDebug("Live playlist already contains #EXT-X-START; leaving as-is");
+            return manifestContent;
+        }
+
+        var targetDurationMatch = Regex.Match(manifestContent, @"#EXT-X-TARGETDURATION:(\d+(?:\.\d+)?)");
+        if (!targetDurationMatch.Success
+            || !double.TryParse(
+                targetDurationMatch.Groups[1].Value,
+                System.Globalization.NumberStyles.Float,
+                System.Globalization.CultureInfo.InvariantCulture,
+                out var targetDuration)
+            || targetDuration <= 0)
+        {
+            _logger.LogDebug("Could not read EXT-X-TARGETDURATION; skipping EXT-X-START injection");
+            return manifestContent;
+        }
+
+        // RFC 8216: TIME-OFFSET SHOULD NOT be within 3 target durations of the live edge.
+        var clampedSegments = Math.Max(3, segmentsBack);
+        var offsetSeconds = clampedSegments * targetDuration;
+        var startTag = string.Format(
+            System.Globalization.CultureInfo.InvariantCulture,
+            "#EXT-X-START:TIME-OFFSET=-{0:0.###},PRECISE=YES",
+            offsetSeconds);
+
+        _logger.LogInformation(
+            "Injecting {StartTag} into live playlist (targetDuration={TargetDuration}s, segmentsBack={SegmentsBack})",
+            startTag,
+            targetDuration,
+            clampedSegments);
+
+        // Insert after the #EXTM3U header so it sits with the other top-level tags.
+        var headerIndex = manifestContent.IndexOf("#EXTM3U", StringComparison.Ordinal);
+        if (headerIndex < 0)
+        {
+            return startTag + "\n" + manifestContent;
+        }
+
+        var lineEnd = manifestContent.IndexOf('\n', headerIndex);
+        if (lineEnd < 0)
+        {
+            return manifestContent + "\n" + startTag;
+        }
+
+        return manifestContent[..(lineEnd + 1)] + startTag + "\n" + manifestContent[(lineEnd + 1)..];
+    }
+
    /// <summary>
    /// Cleans up old and expired stream mappings.
    /// </summary>