From http://kdenlive.org/forum/cant-start-kdnlive-sdl-module-missing-mlt

Kdenlive 0.8 tries to detect mlt by reading from stderr, but between
mlt 0.7.2 and 0.7.4 mlt this has changed from stderr to stdout.
===================================================================
--- kdenlive-0.8/src.orig/wizard.cpp	2011-04-26 21:44:22.000000000 +0200
+++ kdenlive-0.8/src/wizard.cpp	2011-07-21 18:22:18.470831892 +0200
@@ -214,7 +214,7 @@
         button(QWizard::NextButton)->setEnabled(false);
     } else {
         checkProcess.waitForFinished();
-        QByteArray result = checkProcess.readAllStandardError();
+        QByteArray result = checkProcess.readAllStandardOutput();

         // Check MLT avformat module
         QTreeWidgetItem *avformatItem = new QTreeWidgetItem(m_mltCheck.programList, QStringList() << QString() << i18n("Avformat module (FFmpeg)"));
@@ -246,7 +246,7 @@
                     kDebug() << "// Error querying MLT's version";
                 } else {
                     checkProcess.waitForFinished();
-                    mltVersion = checkProcess.readAllStandardError();
+                    mltVersion = checkProcess.readAllStandardOutput();
                     mltVersion = mltVersion.section('\n', 0, 0).simplified();
                     mltVersion = mltVersion.section(' ', -1).simplified();
                     version = 1000 * mltVersion.section('.', 0, 0).toInt() + 100 * mltVersion.section('.', 1, 1).toInt() + mltVersion.section('.', 2, 2).toInt();
@@ -275,7 +275,7 @@
                     kDebug() << "// Error parsing MLT's avformat codecs";
                 } else {
                     checkProcess2.waitForFinished();
-                    QByteArray codecList = checkProcess2.readAllStandardError();
+                    QByteArray codecList = checkProcess2.readAllStandardOutput();
                     QString acodecList(codecList);
                     QStringList result;
                     QStringList alist = acodecList.split('\n', QString::SkipEmptyParts);
@@ -292,7 +292,7 @@
                     kDebug() << "// Error parsing MLT's avformat codecs";
                 } else {
                     checkProcess2.waitForFinished();
-                    QByteArray codecList = checkProcess2.readAllStandardError();
+                    QByteArray codecList = checkProcess2.readAllStandardOutput();
                     QString vcodecList(codecList);
                     QStringList result;
                     QStringList vlist = vcodecList.split('\n', QString::SkipEmptyParts);
@@ -309,7 +309,7 @@
                     kDebug() << "// Error parsing MLT's avformat codecs";
                 } else {
                     checkProcess2.waitForFinished();
-                    QByteArray codecList = checkProcess2.readAllStandardError();
+                    QByteArray codecList = checkProcess2.readAllStandardOutput();
                     QString vcodecList(codecList);
                     QStringList result;
                     QStringList vlist = vcodecList.split('\n', QString::SkipEmptyParts);
@@ -606,7 +606,7 @@

     checkProcess.waitForFinished();

-    QByteArray result = checkProcess.readAllStandardError();
+    QByteArray result = checkProcess.readAllStandardOutput();
     if (!result.contains("- avformat")) errorMessage.append(i18n("MLT's avformat (FFMPEG) module not found. Please check your FFMPEG and MLT install. Kdenlive will not work until this issue is fixed.") + "\n");*/

     QProcess checkProcess2;
@@ -616,7 +616,7 @@

     checkProcess2.waitForFinished();

-    QByteArray result = checkProcess2.readAllStandardError();
+    QByteArray result = checkProcess2.readAllStandardOutput();
     if (!result.contains("sdl") || !result.contains("sdl_preview")) errorMessage.append(i18n("MLT's SDL module not found. Please check your MLT install. Kdenlive will not work until this issue is fixed.") + '\n');

     if (!errorMessage.isEmpty()) {