From 879052472841d584e0aad21ac220131b586c1de5 Mon Sep 17 00:00:00 2001
From: Tim-Philipp Müller <tim@centricular.net>
Date: Mon, 25 Feb 2013 10:38:09 +0000
Subject: avviddec: fix H.264 decoding errors by disabling multi-threaded decoding

Multi-threaded decoding does not work properly with the older libav 0.8
version included in this gst-libav series, so just disable multi-threaded
decoding again entirely for now. (We could also switch from FF_THREAD_SLICE
to FF_THREAD_FRAME, but that may have other side-effects and just disabling
it seems safest for now).

This works properly in git master with more recent libav 0.9.x versions.

Adventurous users may still re-enable this functionality by setting
the GST_AVVIDDEC_MAX_THREADS environment variable to 'auto' or the
max. number of threads desired.

https://bugzilla.gnome.org/show_bug.cgi?id=694230
---
diff --git a/ext/libav/gstavutils.c b/ext/libav/gstavutils.c
index 8555d8d..f7a80f6 100644
--- a/ext/libav/gstavutils.c
+++ b/ext/libav/gstavutils.c
@@ -476,6 +476,7 @@ gst_ffmpeg_auto_max_threads (void)
     if (n < 1)
       n = 1;
 
+    GST_INFO ("threads: %d", n);
     g_once_init_leave (&n_threads, n);
   }
 
diff --git a/ext/libav/gstavviddec.c b/ext/libav/gstavviddec.c
index 669a75d..caf3e2e 100644
--- a/ext/libav/gstavviddec.c
+++ b/ext/libav/gstavviddec.c
@@ -106,7 +106,7 @@ struct _GstFFMpegVidDecClass
 #define DEFAULT_SKIPFRAME		0
 #define DEFAULT_DIRECT_RENDERING	TRUE
 #define DEFAULT_DEBUG_MV		FALSE
-#define DEFAULT_MAX_THREADS		0
+#define DEFAULT_MAX_THREADS		1
 
 enum
 {
@@ -470,14 +470,30 @@ gst_ffmpegviddec_set_format (GstVideoDecoder * decoder,
    * supports it) */
   ffmpegdec->context->debug_mv = ffmpegdec->debug_mv;
 
-  if (ffmpegdec->max_threads == 0) {
-    if (!(oclass->in_plugin->capabilities & CODEC_CAP_AUTO_THREADS))
-      ffmpegdec->context->thread_count = gst_ffmpeg_auto_max_threads ();
-    else
-      ffmpegdec->context->thread_count = 0;
-  } else
-    ffmpegdec->context->thread_count = ffmpegdec->max_threads;
+  {
+    const gchar *env = g_getenv ("GST_AVVIDDEC_MAX_THREADS");
+    int max_threads = ffmpegdec->max_threads;
+
+    if (env != NULL) {
+      if (g_str_equal (env, "auto"))
+        max_threads = 0;
+      else
+        max_threads = MAX (atoi (env), 0);
+
+      if (max_threads != 1) {
+        GST_WARNING_OBJECT (ffmpegdec, "max threads forced to %d, this might "
+            "lead to decoding errors or artefacts", max_threads);
+      }
+    }
 
+    if (max_threads == 0) {
+      if (!(oclass->in_plugin->capabilities & CODEC_CAP_AUTO_THREADS))
+        ffmpegdec->context->thread_count = gst_ffmpeg_auto_max_threads ();
+      else
+        ffmpegdec->context->thread_count = 0;
+    } else
+      ffmpegdec->context->thread_count = max_threads;
+  }
   ffmpegdec->context->thread_type = FF_THREAD_SLICE;
 
   /* open codec - we don't select an output pix_fmt yet,
--
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