buffer: play audio when video buffer is ready. fix cover display

music with cover has a video stream contains only 1 frame. Then audio
buffer should be the primary buffer.
TODO:
- dynamic change buffer value when playing
- change primary buffer if previous primary buffer stream is disabled
bug:
broken backward seeking rtsp://184.72.239.149/vod/
mp4:BigBuckBunny_115k.mov

src/AVDemuxThread.cpp

@@ -20,6 +20,7 @@
 ******************************************************************************/
 
 #include "AVDemuxThread.h"
+#include <limits>
 #include "QtAV/AVClock.h"
 #include "QtAV/AVDemuxer.h"
 #include "QtAV/AVDecoder.h"
@@ -399,7 +400,9 @@ void AVDemuxThread::run()
     qDebug("get av queue a/v thread = %p %p", audio_thread, video_thread);
     PacketBuffer *aqueue = audio_thread ? audio_thread->packetQueue() : 0;
     PacketBuffer *vqueue = video_thread ? video_thread->packetQueue() : 0;
-    m_buffer = vqueue ? vqueue : aqueue;
+    // aqueue as a primary buffer: music with/without cover
+    m_buffer = !vqueue || (aqueue && demuxer->hasAttacedPicture()) ? aqueue : vqueue;
+    const int buf2 = aqueue->bufferValue(); // TODO: may be changed by user
     if (aqueue) {
         aqueue->clear();
         aqueue->setBlocking(true);
@@ -464,9 +467,16 @@ void AVDemuxThread::run()
                     aqueue->clear();
                     continue;
                 }
+                if (m_buffer != aqueue) {
+                    if (m_buffer->isBuffering()) {
+                        aqueue->setBufferValue(std::numeric_limits<int>::max());
+                    } else {
+                        aqueue->setBufferValue(buf2);
+                    }
+                }
                 // always block full if no vqueue because empty callback may set false
                 // attached picture is cover for song, 1 frame
-                aqueue->blockFull(!video_thread || !video_thread->isRunning() || !vqueue || (vqueue->isEnough() || demuxer->hasAttacedPicture()));
+                aqueue->blockFull(!video_thread || !video_thread->isRunning() || !vqueue || demuxer->hasAttacedPicture());
                 aqueue->put(pkt); //affect video_thread
             }
         } else if (index == demuxer->videoStream()) {

src/AVPlayerPrivate.cpp

@@ -404,8 +404,10 @@ bool AVPlayer::Private::setupAudioThread(AVPlayer *player)
     }
     athread->setDecoder(adec);
     player->setAudioOutput(ao);
-    const qreal fps = qMax<qreal>(24.0, statistics.video.frame_rate);
-    int bv = 0.6*fps;
+    // if has video, then audio buffer should not block the video buffer (bufferValue == 1, modified in AVDemuxThread)
+    // TODO: buf if video stream is only a cover picture, audio buffer should be the primary buffer and BufferTime is preferred(call setBufferMode/Value)
+    int bv = statistics.audio.frame_rate > 0 && statistics.audio.frame_rate < 60 ?
+                statistics.audio.frame_rate : 1;
     if (buffer_mode == BufferTime)
         bv = 600; //ms
     else if (buffer_mode == BufferBytes)
@@ -484,6 +486,9 @@ bool AVPlayer::Private::setupVideoThread(AVPlayer *player)
         bv = 600; //ms
     else if (buffer_mode == BufferBytes)
         bv = 1024;
+    // no block for music with cover
+    if (demuxer.hasAttacedPicture() || (statistics.video.frames > 0 && statistics.video.frames < bv))
+        bv = qMax<int>(1, statistics.video.frames);
     vthread->packetQueue()->setBufferMode(buffer_mode);
     vthread->packetQueue()->setBufferValue(buffer_value < 0 ? bv : buffer_value);
     initVideoStatistics(demuxer.videoStream());

src/utils/BlockingQueue.h

@@ -53,6 +53,7 @@ public:
     void blockFull(bool block);
 //TODO:setMinBlock,MaxBlock
     inline void clear();
+    // TODO: checkEmpty, Enough, Full?
     inline bool isEmpty() const;
     inline bool isEnough() const; //size > thres
     inline bool isFull() const; //size >= cap