fix: Partially handles screen-sharing simulcast.

This is the first PR from a (hopefully short) series of PRs that will
implement proper support for simulcast for screen-sharing.

When VP8-based screen-sharing is activated Chrome is sending 2 streams
with the same resolution but with different bitrates and different
temporal layer bitrate allocations. This is different from what the
bridge expects, which is 3 streams with _different_ resolutions. The
different resolutions imply a quality order enabling the bridge to
switch from low quality to high quality and vica-versa.

Since we can no longer rely on the streams having different resolutions,
there's no longer an implicit order that the bridge can detect
on-the-fly, so now we take this information from the signaling.

src/main/java/org/jitsi/videobridge/cc/AdaptiveTrackProjection.java

@@ -184,8 +184,21 @@ public boolean accept(@NotNull RawPacket rtpPacket)
         // suspended so that it can raise the needsKeyframe flag and also allow
         // it to compute a sequence number delta when the target becomes > -1.
 
+        RTPEncodingDesc encoding = getSource()
+            .getMediaStreamTrackReceiver().findRTPEncodingDesc(rtpPacket);
+
+        if (encoding == null)
+        {
+            logger.warn(
+                "Dropping an RTP packet, because the SSRC has not " +
+                    "been signaled:" + rtpPacket.getSSRCAsLong());
+
+            return false;
+        }
+
         int targetIndexCopy = targetIndex;
-        boolean accept = contextCopy.accept(rtpPacket, targetIndexCopy);
+        boolean accept = contextCopy.accept(
+            rtpPacket, encoding.getIndex(), targetIndexCopy);
 
         // We check if the context needs a keyframe regardless of whether or not
         // the packet was accepted.

src/main/java/org/jitsi/videobridge/cc/AdaptiveTrackProjectionContext.java

@@ -45,10 +45,11 @@ public interface AdaptiveTrackProjectionContext
      * Determines whether an RTP packet should be accepted or not.
      *
      * @param rtpPacket the RTP packet to determine whether to accept or not.
+     * @param incomingIndex the quality index of the incoming RTP packet.
      * @param targetIndex the target quality index
      * @return true if the packet should be accepted, false otherwise.
      */
-    boolean accept(RawPacket rtpPacket, int targetIndex);
+    boolean accept(RawPacket rtpPacket, int incomingIndex, int targetIndex);
 
     /**
      * @return true if this stream context needs a keyframe in order to either

src/main/java/org/jitsi/videobridge/cc/GenericAdaptiveTrackProjectionContext.java

@@ -148,12 +148,13 @@ class GenericAdaptiveTrackProjectionContext
      * thread) accessing this method at a time.
      *
      * @param rtpPacket the RTP packet to determine whether to accept or not.
+     * @param incomingIndex the quality index of the
      * @param targetIndex the target quality index
      * @return true if the packet should be accepted, false otherwise.
      */
     @Override
     public synchronized boolean
-    accept(@NotNull RawPacket rtpPacket, int targetIndex)
+    accept(@NotNull RawPacket rtpPacket, int incomingIndex, int targetIndex)
     {
         if (targetIndex == RTPEncodingDesc.SUSPENDED_INDEX)
         {

src/main/java/org/jitsi/videobridge/cc/vp8/VP8AdaptiveTrackProjectionContext.java

@@ -191,12 +191,13 @@ public VP8AdaptiveTrackProjectionContext(
      * method at a time.
      *
      * @param rtpPacket the VP8 packet to decide whether or not to project.
-     * @param targetIndex
+     * @param incomingIndex the quality index of the incoming RTP packet
+     * @param targetIndex the target quality index we want to achieve
      * @return true to project the packet, otherwise false.
      */
     private synchronized
     VP8FrameProjection createVP8FrameProjection(
-        @NotNull RawPacket rtpPacket, int targetIndex)
+        @NotNull RawPacket rtpPacket, int incomingIndex, int targetIndex)
     {
         // Creating a new VP8 projection depends on reading and results in
         // writing of the last VP8 frame, therefore this method needs to be
@@ -236,7 +237,8 @@ VP8FrameProjection createVP8FrameProjection(
         // Lastly, check whether the quality of the frame is something that we
         // want to forward. We don't want to be allocating new objects unless
         // we're interested in the quality of this frame.
-        if (!vp8QualityFilter.acceptFrame(rtpPacket, targetIndex, nowMs))
+        if (!vp8QualityFilter.acceptFrame(
+            rtpPacket, incomingIndex, targetIndex, nowMs))
         {
             return null;
         }
@@ -349,18 +351,21 @@ public boolean needsKeyframe()
      * Determines whether a packet should be accepted or not.
      *
      * @param rtpPacket the RTP packet to determine whether to project or not.
-     * @param targetIndex the target index to achieve
+     * @param incomingIndex the quality index of the incoming RTP packet
+     * @param targetIndex the target quality index we want to achieve
      * @return true if the packet should be accepted, false otherwise.
      */
     @Override
-    public boolean accept(@NotNull RawPacket rtpPacket, int targetIndex)
+    public boolean accept(
+        @NotNull RawPacket rtpPacket, int incomingIndex, int targetIndex)
     {
         VP8FrameProjection vp8FrameProjection
             = lookupVP8FrameProjection(rtpPacket);
 
         if (vp8FrameProjection == null)
         {
-            vp8FrameProjection = createVP8FrameProjection(rtpPacket, targetIndex);
+            vp8FrameProjection
+                = createVP8FrameProjection(rtpPacket, incomingIndex, targetIndex);
         }
 
         return vp8FrameProjection != null

src/main/java/org/jitsi/videobridge/cc/vp8/VP8QualityFilter.java

@@ -20,8 +20,6 @@
 import org.jitsi.service.neomedia.*;
 import org.jitsi.util.*;
 
-import java.util.*;
-
 /**
  * This class is responsible for dropping VP8 simulcast/svc packets based on
  * their quality, i.e. packets that correspond to qualities that are above a
@@ -44,22 +42,10 @@ class VP8QualityFilter
      */
     private static final int MIN_KEY_FRAME_WAIT_MS = 300;
 
-    /**
-     * Constants that define the minimum heights that a VP8 stream needs to have
-     * in order to be considered HD, SD or LD.
-     */
-    private static final int MIN_HD_HEIGHT = 540, MIN_SD_HEIGHT = 360;
-
     /**
      * The HD, SD, LD and suspended spatial/quality layer IDs.
      */
-    private static final int HD_LAYER_ID = 2, SD_LAYER_ID = 1,
-        LD_LAYER_ID = 0, SUSPENDED_LAYER_ID = -1;
-
-    /**
-     * A map that caches the spatial/quality layer ID of each simulcast SSRC.
-     */
-    private final Map<Long, Integer> ssrcToSpatialLayerQuality = new HashMap<>();
+    private static final int SUSPENDED_LAYER_ID = -1;
 
     /**
      * Holds the arrival time (in millis) of the most recent keyframe group.
@@ -94,85 +80,6 @@ class VP8QualityFilter
      */
     private int currentSpatialLayerId = SUSPENDED_LAYER_ID;
 
-    /**
-     * Gets the spatial/quality layer ID of a packet. Before this method is able
-     * to return a meaningful value (not -1) it has to have received at least
-     * one keyframe from the SSRC that is queried.
-     *
-     * @param firstPacketOfFrame the RTP packet whose spatial/quality layer
-     * index needs to be returned.
-     * @param isKeyframe a boolean that indicates whether or not the packet that
-     * is specified as an argument is a keyframe
-     * @return the spatial/quality index of the packet that is specified as an
-     * argument, or -1 in case it's impossible to resolve.
-     */
-    private int getSpatialLayerIndex(
-        @NotNull RawPacket firstPacketOfFrame, boolean isKeyframe)
-    {
-        long ssrc = firstPacketOfFrame.getSSRCAsLong();
-        if (ssrcToSpatialLayerQuality.containsKey(ssrc))
-        {
-            return ssrcToSpatialLayerQuality.get(ssrc);
-        }
-        else if (isKeyframe)
-        {
-            int spatialLayerId
-                = getSpatialLayerIndexFromKeyframe(firstPacketOfFrame);
-            if (spatialLayerId > -1)
-            {
-                ssrcToSpatialLayerQuality.put(ssrc, spatialLayerId);
-            }
-
-            return spatialLayerId;
-        }
-        {
-            return -1;
-        }
-    }
-
-    /**
-     * Gets the spatial/quality layer ID of a packet. The specified packet MUST
-     * be a VP8 keyframe because the frame height, which allows us to map the
-     * different simulcast layers into spatial/quality layer IDs, are found in
-     * the keyframe header.
-     *
-     * @param firstPacketOfKeyframe the first packet of a keyframe to map/get
-     * its spatial/quality layer id.
-     * @return the spatial/quality layer id of the packet.
-     */
-    private static int getSpatialLayerIndexFromKeyframe(
-        @NotNull RawPacket firstPacketOfKeyframe)
-    {
-        byte[] buf = firstPacketOfKeyframe.getBuffer();
-        int payloadOffset = firstPacketOfKeyframe.getPayloadOffset(),
-            payloadLen = firstPacketOfKeyframe.getPayloadLength(),
-            payloadHeaderLen = 3;
-
-        int payloadDescriptorLen = DePacketizer
-            .VP8PayloadDescriptor.getSize(buf, payloadOffset, payloadLen);
-
-        int height = DePacketizer.VP8KeyframeHeader.getHeight(
-            buf, payloadOffset + payloadDescriptorLen + payloadHeaderLen);
-
-        if (height >= MIN_HD_HEIGHT)
-        {
-            return HD_LAYER_ID;
-        }
-        else if (height >= MIN_SD_HEIGHT)
-        {
-            return SD_LAYER_ID;
-        }
-        else if (height > -1)
-        {
-            return LD_LAYER_ID;
-        }
-        else
-        {
-            // Some error occurred.
-            return -1;
-        }
-    }
-
     /**
      * @return true if a the target spatial/quality layer id has changed and a
      * keyframe hasn't been received yet, false otherwise.
@@ -192,13 +99,15 @@ boolean needsKeyframe()
      * method at a time.
      *
      * @param firstPacketOfFrame the first packet of the VP8 frame.
+     * @param incomingIndex the quality index of the incoming RTP packet
      * @param externalTargetIndex the target quality index that the user of this
      * instance wants to achieve.
      * @param nowMs the current time (in millis)
      * @return true to accept the VP8 frame, otherwise false.
      */
     synchronized boolean acceptFrame(
         @NotNull RawPacket firstPacketOfFrame,
+        int incomingIndex,
         int externalTargetIndex, long nowMs)
     {
         // We make local copies of the externalTemporalLayerIdTarget and the
@@ -245,14 +154,15 @@ synchronized boolean acceptFrame(
             temporalLayerIdOfFrame = 0;
         }
 
+        int spatialLayerId = getSpatialLayerId(incomingIndex);
         if (DePacketizer.isKeyFrame(buf, payloadOff, payloadLen))
         {
-            return acceptKeyframe(firstPacketOfFrame, nowMs);
+            return acceptKeyframe(spatialLayerId, nowMs);
         }
         else if (currentSpatialLayerId > SUSPENDED_LAYER_ID)
         {
             if (!isInSwitchingPhase(nowMs)
-                && isPossibleToSwitch(firstPacketOfFrame))
+                && isPossibleToSwitch(firstPacketOfFrame, spatialLayerId))
             {
                 needsKeyframe = true;
             }
@@ -311,10 +221,8 @@ private synchronized boolean isInSwitchingPhase(long nowMs)
      * method for specific details).
      */
     private synchronized boolean isPossibleToSwitch(
-        @NotNull RawPacket firstPacketOfFrame)
+        @NotNull RawPacket firstPacketOfFrame, int spatialLayerId)
     {
-        int spatialLayerId
-            = getSpatialLayerIndex(firstPacketOfFrame, false);
         if (spatialLayerId == -1)
         {
             // We failed to resolve the spatial/quality layer of the packet.
@@ -347,19 +255,15 @@ else if (spatialLayerId < currentSpatialLayerId
      * synchronized keyword because there's only one thread accessing this
      * method at a time.
      *
-     * @param firstPacketOfKeyframe the first packet of a VP8 keyframe.
      * @param nowMs the current time (in millis)
      * @return true to accept the VP8 keyframe, otherwise false.
      */
     private synchronized boolean acceptKeyframe(
-        @NotNull RawPacket firstPacketOfKeyframe, long nowMs)
+        int spatialLayerIdOfKeyframe, long nowMs)
     {
         // This branch writes the {@link #currentSpatialLayerId} and it
         // determines whether or not we should switch to another simulcast
         // stream.
-
-        int spatialLayerIdOfKeyframe
-            = getSpatialLayerIndex(firstPacketOfKeyframe, true);
         if (spatialLayerIdOfKeyframe < 0)
         {
             // something went terribly wrong, normally we should be able to