Add QIODevice output to the recording engine

The reasons for picking the change are:
- ensuring code consistency to avoid merge conflicts
- the ticket QTBUG-122224, which is going to be fixed in
  in the next patch.

The IO is expected to be open, it's to be described in
the documentation.

Task-number: QTBUG-122224
Task-number: QTBUG-121827
Pick-to: 6.5
Change-Id: I82fbfac7b508032600dd8eb080528e23c0ee2e59
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
Reviewed-by: Bartlomiej Moskal <bartlomiej.moskal@qt.io>
(cherry picked from commit 12211d0cdbbc0845b753d8e9fffa481c053be751)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 140d47e915485d7e568208d199429b9823f3b65d)

6 files changed, 56 insertions, 6 deletions

diff --git a/src/plugins/multimedia/ffmpeg/qffmpegencoder.cpp b/src/plugins/multimedia/ffmpeg/qffmpegencoder.cpp
index d233ac895..85ac70f87 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpegencoder.cpp
+++ b/src/plugins/multimedia/ffmpeg/qffmpegencoder.cpp
@@ -46,10 +46,15 @@ T dequeueIfPossible(std::queue<T> &queue)
 
 } // namespace
 
-Encoder::Encoder(const QMediaEncoderSettings &settings, const QString &filePath)
+Encoder::Encoder(const QMediaEncoderSettings &settings, Output output)
     : m_settings(settings), m_formatContext(settings.fileFormat())
 {
-    m_formatContext.openAVIO(filePath);
+    auto openAVIO = [this](const auto &output) { m_formatContext.openAVIO(output); };
+    std::visit(openAVIO, output);
+
+    if (!m_formatContext.isAVIOOpen())
+        qCWarning(qLcFFmpegEncoder) << "Unable to open IO device to record media";
+
     m_muxer = new Muxer(this);
 }
 
diff --git a/src/plugins/multimedia/ffmpeg/qffmpegencoder_p.h b/src/plugins/multimedia/ffmpeg/qffmpegencoder_p.h
index da9c26ac8..7d74baa03 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpegencoder_p.h
+++ b/src/plugins/multimedia/ffmpeg/qffmpegencoder_p.h
@@ -27,6 +27,7 @@
 #include <qmediarecorder.h>
 
 #include <queue>
+#include <variant>
 
 QT_BEGIN_NAMESPACE
 
@@ -58,7 +59,8 @@ class Encoder : public QObject
 {
     Q_OBJECT
 public:
-    Encoder(const QMediaEncoderSettings &settings, const QString &filePath);
+    using Output = std::variant<QString, QIODevice *>;
+    Encoder(const QMediaEncoderSettings &settings, Output output);
     ~Encoder();
 
     void addAudioInput(QFFmpegAudioInput *input);
diff --git a/src/plugins/multimedia/ffmpeg/qffmpegencodingformatcontext.cpp b/src/plugins/multimedia/ffmpeg/qffmpegencodingformatcontext.cpp
index a06b46ef2..908fbe028 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpegencodingformatcontext.cpp
+++ b/src/plugins/multimedia/ffmpeg/qffmpegencodingformatcontext.cpp
@@ -3,6 +3,8 @@
 
 #include "qffmpegencodingformatcontext_p.h"
 #include "qffmpegmediaformatinfo_p.h"
+#include "qffmpegioutils_p.h"
+#include "qiodevice.h"
 #include "QtCore/qloggingcategory.h"
 
 QT_BEGIN_NAMESPACE
@@ -11,6 +13,12 @@ namespace QFFmpeg {
 
 static Q_LOGGING_CATEGORY(qLcEncodingFormatContext, "qt.multimedia.ffmpeg.encodingformatcontext");
 
+namespace {
+// In the example https://ffmpeg.org/doxygen/trunk/avio_read_callback_8c-example.html,
+// BufferSize = 4096 is suggested, however, it might be not optimal. To be investigated.
+constexpr size_t DefaultBufferSize = 4096;
+} // namespace
+
 EncodingFormatContext::EncodingFormatContext(QMediaFormat::FileFormat fileFormat)
     : m_avFormatContext(avformat_alloc_context())
 {
@@ -46,12 +54,30 @@ void EncodingFormatContext::openAVIO(const QString &filePath)
         m_avFormatContext->url = url.release();
 }
 
+void EncodingFormatContext::openAVIO(QIODevice *device)
+{
+    Q_ASSERT(!isAVIOOpen());
+    Q_ASSERT(device);
+
+    if (!device->isWritable())
+        return;
+
+    auto buffer = static_cast<uint8_t *>(av_malloc(DefaultBufferSize));
+    m_avFormatContext->pb = avio_alloc_context(buffer, DefaultBufferSize, 1, device, nullptr,
+                                               &writeQIODevice, &seekQIODevice);
+}
+
 void EncodingFormatContext::closeAVIO()
 {
     // Close the AVIOContext and release any file handles
-    if (auto io = std::exchange(m_avFormatContext->pb, nullptr)) {
-        const int res = avio_close(io);
-        Q_ASSERT(res == 0);
+    if (isAVIOOpen()) {
+        if (m_avFormatContext->url && *m_avFormatContext->url != '\0') {
+            auto closeResult = avio_closep(&m_avFormatContext->pb);
+            Q_ASSERT(closeResult == 0);
+        } else {
+            av_free(std::exchange(m_avFormatContext->pb->buffer, nullptr));
+            avio_context_free(&m_avFormatContext->pb);
+        }
 
         // delete url even though it might be delete by avformat_free_context to
         // ensure consistency in openAVIO/closeAVIO.
diff --git a/src/plugins/multimedia/ffmpeg/qffmpegencodingformatcontext_p.h b/src/plugins/multimedia/ffmpeg/qffmpegencodingformatcontext_p.h
index 0993c03ac..bbfb08338 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpegencodingformatcontext_p.h
+++ b/src/plugins/multimedia/ffmpeg/qffmpegencodingformatcontext_p.h
@@ -20,6 +20,8 @@
 
 QT_BEGIN_NAMESPACE
 
+class QIODevice;
+
 namespace QFFmpeg {
 
 class EncodingFormatContext
@@ -30,6 +32,8 @@ public:
 
     void openAVIO(const QString &filePath);
 
+    void openAVIO(QIODevice *device);
+
     bool isAVIOOpen() const { return m_avFormatContext->pb != nullptr; }
 
     void closeAVIO();
diff --git a/src/plugins/multimedia/ffmpeg/qffmpegioutils.cpp b/src/plugins/multimedia/ffmpeg/qffmpegioutils.cpp
index de332e91d..289821832 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpegioutils.cpp
+++ b/src/plugins/multimedia/ffmpeg/qffmpegioutils.cpp
@@ -12,14 +12,25 @@ namespace QFFmpeg {
 int readQIODevice(void *opaque, uint8_t *buf, int buf_size)
 {
     auto *dev = static_cast<QIODevice *>(opaque);
+    Q_ASSERT(dev);
+
     if (dev->atEnd())
         return AVERROR_EOF;
     return dev->read(reinterpret_cast<char *>(buf), buf_size);
 }
 
+int writeQIODevice(void *opaque, uint8_t *buf, int buf_size)
+{
+    auto dev = static_cast<QIODevice *>(opaque);
+    Q_ASSERT(dev);
+
+    return dev->write(reinterpret_cast<const char *>(buf), buf_size);
+}
+
 int64_t seekQIODevice(void *opaque, int64_t offset, int whence)
 {
     QIODevice *dev = static_cast<QIODevice *>(opaque);
+    Q_ASSERT(dev);
 
     if (dev->isSequential())
         return AVERROR(EINVAL);
diff --git a/src/plugins/multimedia/ffmpeg/qffmpegioutils_p.h b/src/plugins/multimedia/ffmpeg/qffmpegioutils_p.h
index cf3136f39..3f6591244 100644
--- a/src/plugins/multimedia/ffmpeg/qffmpegioutils_p.h
+++ b/src/plugins/multimedia/ffmpeg/qffmpegioutils_p.h
@@ -23,6 +23,8 @@ namespace QFFmpeg {
 
 int readQIODevice(void *opaque, uint8_t *buf, int buf_size);
 
+int writeQIODevice(void *opaque, uint8_t *buf, int buf_size);
+
 int64_t seekQIODevice(void *opaque, int64_t offset, int whence);
 
 } // namespace QFFmpeg