diff --git a/library/src/main/java/com/google/android/exoplayer/SampleSource.java b/library/src/main/java/com/google/android/exoplayer/SampleSource.java
index 8e2afc32d6..9c5d6aa303 100644
--- a/library/src/main/java/com/google/android/exoplayer/SampleSource.java
+++ b/library/src/main/java/com/google/android/exoplayer/SampleSource.java
@@ -54,8 +54,8 @@ public interface SampleSource {
    * Prepares the source.
    * <p>
    * Preparation may require reading from the data source (e.g. to determine the available tracks
-   * and formats). If insufficient data is available then the call will return rather than block.
-   * The method can be called repeatedly until the return value indicates success.
+   * and formats). If insufficient data is available then the call will return {@code false} rather
+   * than block. The method can be called repeatedly until the return value indicates success.
    *
    * @return True if the source was prepared successfully, false otherwise.
    * @throws IOException If an error occurred preparing the source.
diff --git a/library/src/main/java/com/google/android/exoplayer/chunk/ChunkSampleSource.java b/library/src/main/java/com/google/android/exoplayer/chunk/ChunkSampleSource.java
index b874f09597..33a4d08a7d 100644
--- a/library/src/main/java/com/google/android/exoplayer/chunk/ChunkSampleSource.java
+++ b/library/src/main/java/com/google/android/exoplayer/chunk/ChunkSampleSource.java
@@ -160,6 +160,7 @@ public class ChunkSampleSource implements SampleSource, Loader.Listener {
   private int currentLoadableExceptionCount;
   private long currentLoadableExceptionTimestamp;
 
+  private MediaFormat downstreamMediaFormat;
   private volatile Format downstreamFormat;
 
   public ChunkSampleSource(ChunkSource chunkSource, LoadControl loadControl,
@@ -221,6 +222,7 @@ public class ChunkSampleSource implements SampleSource, Loader.Listener {
     chunkSource.enable();
     loadControl.register(this, bufferSizeContribution);
     downstreamFormat = null;
+    downstreamMediaFormat = null;
     downstreamPositionUs = timeUs;
     lastSeekPositionUs = timeUs;
     restartFrom(timeUs);
@@ -288,21 +290,30 @@ public class ChunkSampleSource implements SampleSource, Loader.Listener {
         return readData(track, playbackPositionUs, formatHolder, sampleHolder, false);
       } else if (mediaChunk.isLastChunk()) {
         return END_OF_STREAM;
-      } else {
-        IOException chunkSourceException = chunkSource.getError();
-        if (chunkSourceException != null) {
-          throw chunkSourceException;
-        }
-        return NOTHING_READ;
       }
-    } else if (downstreamFormat == null || !downstreamFormat.id.equals(mediaChunk.format.id)) {
+      IOException chunkSourceException = chunkSource.getError();
+      if (chunkSourceException != null) {
+        throw chunkSourceException;
+      }
+      return NOTHING_READ;
+    }
+
+    if (downstreamFormat == null || !downstreamFormat.equals(mediaChunk.format)) {
       notifyDownstreamFormatChanged(mediaChunk.format.id, mediaChunk.trigger,
           mediaChunk.startTimeUs);
-      MediaFormat format = mediaChunk.getMediaFormat();
-      chunkSource.getMaxVideoDimensions(format);
-      formatHolder.format = format;
-      formatHolder.drmInitData = mediaChunk.getPsshInfo();
       downstreamFormat = mediaChunk.format;
+    }
+
+    if (!mediaChunk.prepare()) {
+      return NOTHING_READ;
+    }
+
+    MediaFormat mediaFormat = mediaChunk.getMediaFormat();
+    if (downstreamMediaFormat == null || !downstreamMediaFormat.equals(mediaFormat)) {
+      chunkSource.getMaxVideoDimensions(mediaFormat);
+      formatHolder.format = mediaFormat;
+      formatHolder.drmInitData = mediaChunk.getPsshInfo();
+      downstreamMediaFormat = mediaFormat;
       return FORMAT_READ;
     }
 
diff --git a/library/src/main/java/com/google/android/exoplayer/chunk/Format.java b/library/src/main/java/com/google/android/exoplayer/chunk/Format.java
index 4aabe601dc..b33fb3aeea 100644
--- a/library/src/main/java/com/google/android/exoplayer/chunk/Format.java
+++ b/library/src/main/java/com/google/android/exoplayer/chunk/Format.java
@@ -15,6 +15,8 @@
  */
 package com.google.android.exoplayer.chunk;
 
+import com.google.android.exoplayer.util.Assertions;
+
 import java.util.Comparator;
 
 /**
@@ -97,7 +99,7 @@ public class Format {
    */
   public Format(String id, String mimeType, int width, int height, int numChannels,
       int audioSamplingRate, int bandwidth) {
-    this.id = id;
+    this.id = Assertions.checkNotNull(id);
     this.mimeType = mimeType;
     this.width = width;
     this.height = height;
@@ -106,4 +108,19 @@ public class Format {
     this.bandwidth = bandwidth;
   }
 
+  /**
+   * Implements equality based on {@link #id} only.
+   */
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) {
+      return true;
+    }
+    if (obj == null || getClass() != obj.getClass()) {
+      return false;
+    }
+    Format other = (Format) obj;
+    return other.id.equals(id);
+  }
+
 }
diff --git a/library/src/main/java/com/google/android/exoplayer/chunk/MediaChunk.java b/library/src/main/java/com/google/android/exoplayer/chunk/MediaChunk.java
index fd7c3a59b6..51ebac65c2 100644
--- a/library/src/main/java/com/google/android/exoplayer/chunk/MediaChunk.java
+++ b/library/src/main/java/com/google/android/exoplayer/chunk/MediaChunk.java
@@ -87,8 +87,22 @@ public abstract class MediaChunk extends Chunk {
    */
   public abstract boolean seekTo(long positionUs, boolean allowNoop);
 
+  /**
+   * Prepares the chunk for reading. Does nothing if the chunk is already prepared.
+   * <p>
+   * Preparation may require consuming some of the chunk. If the data is not yet available then
+   * this method will return {@code false} rather than block. The method can be called repeatedly
+   * until the return value indicates success.
+   *
+   * @return True if the chunk was prepared. False otherwise.
+   * @throws ParserException If an error occurs parsing the media data.
+   */
+  public abstract boolean prepare() throws ParserException;
+
   /**
    * Reads the next media sample from the chunk.
+   * <p>
+   * Should only be called after the chunk has been successfully prepared.
    *
    * @param holder A holder to store the read sample.
    * @return True if a sample was read. False if more data is still required.
@@ -99,6 +113,8 @@ public abstract class MediaChunk extends Chunk {
 
   /**
    * Returns the media format of the samples contained within this chunk.
+   * <p>
+   * Should only be called after the chunk has been successfully prepared.
    *
    * @return The sample media format.
    */
@@ -106,6 +122,8 @@ public abstract class MediaChunk extends Chunk {
 
   /**
    * Returns the pssh information associated with the chunk.
+   * <p>
+   * Should only be called after the chunk has been successfully prepared.
    *
    * @return The pssh information.
    */
diff --git a/library/src/main/java/com/google/android/exoplayer/chunk/Mp4MediaChunk.java b/library/src/main/java/com/google/android/exoplayer/chunk/Mp4MediaChunk.java
index 4bd0076a6d..8aaee879e4 100644
--- a/library/src/main/java/com/google/android/exoplayer/chunk/Mp4MediaChunk.java
+++ b/library/src/main/java/com/google/android/exoplayer/chunk/Mp4MediaChunk.java
@@ -33,24 +33,34 @@ import java.util.UUID;
 public final class Mp4MediaChunk extends MediaChunk {
 
   private final FragmentedMp4Extractor extractor;
+  private final boolean maybeSelfContained;
   private final long sampleOffsetUs;
 
+  private boolean prepared;
+  private MediaFormat mediaFormat;
+  private Map<UUID, byte[]> psshInfo;
+
   /**
    * @param dataSource A {@link DataSource} for loading the data.
    * @param dataSpec Defines the data to be loaded.
    * @param format The format of the stream to which this chunk belongs.
-   * @param extractor The extractor that will be used to extract the samples.
    * @param trigger The reason for this chunk being selected.
    * @param startTimeUs The start time of the media contained by the chunk, in microseconds.
    * @param endTimeUs The end time of the media contained by the chunk, in microseconds.
-   * @param sampleOffsetUs An offset to subtract from the sample timestamps parsed by the extractor.
    * @param nextChunkIndex The index of the next chunk, or -1 if this is the last chunk.
+   * @param extractor The extractor that will be used to extract the samples.
+   * @param maybeSelfContained Set to true if this chunk might be self contained, meaning it might
+   *     contain a moov atom defining the media format of the chunk. This parameter can always be
+   *     safely set to true. Setting to false where the chunk is known to not be self contained may
+   *     improve startup latency.
+   * @param sampleOffsetUs An offset to subtract from the sample timestamps parsed by the extractor.
    */
   public Mp4MediaChunk(DataSource dataSource, DataSpec dataSpec, Format format,
-      int trigger, FragmentedMp4Extractor extractor, long startTimeUs, long endTimeUs,
-      long sampleOffsetUs, int nextChunkIndex) {
+      int trigger, long startTimeUs, long endTimeUs, int nextChunkIndex,
+      FragmentedMp4Extractor extractor, boolean maybeSelfContained, long sampleOffsetUs) {
     super(dataSource, dataSpec, format, trigger, startTimeUs, endTimeUs, nextChunkIndex);
     this.extractor = extractor;
+    this.maybeSelfContained = maybeSelfContained;
     this.sampleOffsetUs = sampleOffsetUs;
   }
 
@@ -70,6 +80,29 @@ public final class Mp4MediaChunk extends MediaChunk {
     return isDiscontinuous;
   }
 
+  @Override
+  public boolean prepare() throws ParserException {
+    if (!prepared) {
+      if (maybeSelfContained) {
+        // Read up to the first sample. Once we're there, we know that the extractor must have
+        // parsed a moov atom if the chunk contains one.
+        NonBlockingInputStream inputStream = getNonBlockingInputStream();
+        Assertions.checkState(inputStream != null);
+        int result = extractor.read(inputStream, null);
+        prepared = (result & FragmentedMp4Extractor.RESULT_NEED_SAMPLE_HOLDER) != 0;
+      } else {
+        // We know there isn't a moov atom. The extractor must have parsed one from a separate
+        // initialization chunk.
+        prepared = true;
+      }
+      if (prepared) {
+        mediaFormat = Assertions.checkNotNull(extractor.getFormat());
+        psshInfo = extractor.getPsshInfo();
+      }
+    }
+    return prepared;
+  }
+
   @Override
   public boolean read(SampleHolder holder) throws ParserException {
     NonBlockingInputStream inputStream = getNonBlockingInputStream();
@@ -84,12 +117,12 @@ public final class Mp4MediaChunk extends MediaChunk {
 
   @Override
   public MediaFormat getMediaFormat() {
-    return extractor.getFormat();
+    return mediaFormat;
   }
 
   @Override
   public Map<UUID, byte[]> getPsshInfo() {
-    return extractor.getPsshInfo();
+    return psshInfo;
   }
 
 }
diff --git a/library/src/main/java/com/google/android/exoplayer/chunk/SingleSampleMediaChunk.java b/library/src/main/java/com/google/android/exoplayer/chunk/SingleSampleMediaChunk.java
index ef7e1436a0..6fa2f08962 100644
--- a/library/src/main/java/com/google/android/exoplayer/chunk/SingleSampleMediaChunk.java
+++ b/library/src/main/java/com/google/android/exoplayer/chunk/SingleSampleMediaChunk.java
@@ -77,6 +77,11 @@ public class SingleSampleMediaChunk extends MediaChunk {
     this.headerData = headerData;
   }
 
+  @Override
+  public boolean prepare() {
+    return true;
+  }
+
   @Override
   public boolean read(SampleHolder holder) {
     NonBlockingInputStream inputStream = getNonBlockingInputStream();
diff --git a/library/src/main/java/com/google/android/exoplayer/chunk/WebmMediaChunk.java b/library/src/main/java/com/google/android/exoplayer/chunk/WebmMediaChunk.java
index 23dfa2bf0a..f7ca26244a 100644
--- a/library/src/main/java/com/google/android/exoplayer/chunk/WebmMediaChunk.java
+++ b/library/src/main/java/com/google/android/exoplayer/chunk/WebmMediaChunk.java
@@ -64,6 +64,11 @@ public final class WebmMediaChunk extends MediaChunk {
     return isDiscontinuous;
   }
 
+  @Override
+  public boolean prepare() {
+    return true;
+  }
+
   @Override
   public boolean read(SampleHolder holder) {
     NonBlockingInputStream inputStream = getNonBlockingInputStream();
diff --git a/library/src/main/java/com/google/android/exoplayer/dash/DashMp4ChunkSource.java b/library/src/main/java/com/google/android/exoplayer/dash/DashMp4ChunkSource.java
index e975660497..4bf07c1b3a 100644
--- a/library/src/main/java/com/google/android/exoplayer/dash/DashMp4ChunkSource.java
+++ b/library/src/main/java/com/google/android/exoplayer/dash/DashMp4ChunkSource.java
@@ -231,8 +231,8 @@ public class DashMp4ChunkSource implements ChunkSource {
 
     DataSpec dataSpec = new DataSpec(representation.uri, offset, size,
         representation.getCacheKey());
-    return new Mp4MediaChunk(dataSource, dataSpec, representation.format, trigger, extractor,
-        startTimeUs, endTimeUs, 0, nextIndex);
+    return new Mp4MediaChunk(dataSource, dataSpec, representation.format, trigger, startTimeUs,
+        endTimeUs, nextIndex, extractor, false, 0);
   }
 
   private static class InitializationMp4Loadable extends Chunk {
diff --git a/library/src/main/java/com/google/android/exoplayer/parser/mp4/FragmentedMp4Extractor.java b/library/src/main/java/com/google/android/exoplayer/parser/mp4/FragmentedMp4Extractor.java
index 9c44999e80..16e1788943 100644
--- a/library/src/main/java/com/google/android/exoplayer/parser/mp4/FragmentedMp4Extractor.java
+++ b/library/src/main/java/com/google/android/exoplayer/parser/mp4/FragmentedMp4Extractor.java
@@ -83,9 +83,13 @@ public final class FragmentedMp4Extractor {
    * A sidx atom was read. The parsed data can be read using {@link #getSegmentIndex()}.
    */
   public static final int RESULT_READ_SIDX = 32;
+  /**
+   * The next thing to be read is a sample, but a {@link SampleHolder} was not supplied.
+   */
+  public static final int RESULT_NEED_SAMPLE_HOLDER = 64;
 
   private static final int READ_TERMINATING_RESULTS = RESULT_NEED_MORE_DATA | RESULT_END_OF_STREAM
-      | RESULT_READ_SAMPLE_FULL;
+      | RESULT_READ_SAMPLE_FULL | RESULT_NEED_SAMPLE_HOLDER;
   private static final byte[] NAL_START_CODE = new byte[] {0, 0, 0, 1};
   private static final byte[] PIFF_SAMPLE_ENCRYPTION_BOX_EXTENDED_TYPE =
       new byte[] {-94, 57, 79, 82, 90, -101, 79, 20, -94, 68, 108, 66, 124, 100, -115, -12};
@@ -272,7 +276,8 @@ public final class FragmentedMp4Extractor {
    * in subsequent calls until the whole sample has been read.
    *
    * @param inputStream The input stream from which data should be read.
-   * @param out A {@link SampleHolder} into which the sample should be read.
+   * @param out A {@link SampleHolder} into which the next sample should be read. If null then
+   *     {@link #RESULT_NEED_SAMPLE_HOLDER} will be returned once a sample has been reached.
    * @return One or more of the {@code RESULT_*} flags defined in this class.
    * @throws ParserException If an error occurs parsing the media data.
    */
@@ -1142,6 +1147,9 @@ public final class FragmentedMp4Extractor {
 
   @SuppressLint("InlinedApi")
   private int readSample(NonBlockingInputStream inputStream, SampleHolder out) {
+    if (out == null) {
+      return RESULT_NEED_SAMPLE_HOLDER;
+    }
     int sampleSize = fragmentRun.sampleSizeTable[sampleIndex];
     ByteBuffer outputData = out.data;
     if (parserState == STATE_READING_SAMPLE_START) {
diff --git a/library/src/main/java/com/google/android/exoplayer/parser/webm/DefaultWebmExtractor.java b/library/src/main/java/com/google/android/exoplayer/parser/webm/DefaultWebmExtractor.java
index b0b0936fe1..351eff32d9 100644
--- a/library/src/main/java/com/google/android/exoplayer/parser/webm/DefaultWebmExtractor.java
+++ b/library/src/main/java/com/google/android/exoplayer/parser/webm/DefaultWebmExtractor.java
@@ -36,7 +36,7 @@ import java.util.concurrent.TimeUnit;
  * More info about WebM is <a href="http://www.webmproject.org/code/specs/container/">here</a>.
  */
 @TargetApi(16)
-public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandler {
+public final class DefaultWebmExtractor implements WebmExtractor {
 
   private static final String DOC_TYPE_WEBM = "webm";
   private static final String CODEC_ID_VP9 = "V_VP9";
@@ -104,7 +104,7 @@ public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandl
 
   /* package */ DefaultWebmExtractor(EbmlReader reader) {
     this.reader = reader;
-    this.reader.setEventHandler(this);
+    this.reader.setEventHandler(new InnerEbmlEventHandler());
     this.cueTimesUs = new LongArray();
     this.cueClusterPositions = new LongArray();
   }
@@ -150,8 +150,7 @@ public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandl
     return format;
   }
 
-  @Override
-  public int getElementType(int id) {
+  /* package */ int getElementType(int id) {
     switch (id) {
       case ID_EBML:
       case ID_SEGMENT:
@@ -185,8 +184,7 @@ public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandl
     }
   }
 
-  @Override
-  public boolean onMasterElementStart(
+  /* package */ boolean onMasterElementStart(
       int id, long elementOffsetBytes, int headerSizeBytes, long contentsSizeBytes) {
     switch (id) {
       case ID_SEGMENT:
@@ -205,8 +203,7 @@ public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandl
     return true;
   }
 
-  @Override
-  public boolean onMasterElementEnd(int id) {
+  /* package */ boolean onMasterElementEnd(int id) {
     if (id == ID_CUES) {
       finishPreparing();
       return false;
@@ -214,8 +211,7 @@ public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandl
     return true;
   }
 
-  @Override
-  public boolean onIntegerElement(int id, long value) {
+  /* package */ boolean onIntegerElement(int id, long value) {
     switch (id) {
       case ID_EBML_READ_VERSION:
         // Validate that EBMLReadVersion is supported. This extractor only supports v1.
@@ -253,16 +249,14 @@ public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandl
     return true;
   }
 
-  @Override
-  public boolean onFloatElement(int id, double value) {
+  /* package */ boolean onFloatElement(int id, double value) {
     if (id == ID_DURATION) {
       durationUs = scaleTimecodeToUs((long) value);
     }
     return true;
   }
 
-  @Override
-  public boolean onStringElement(int id, String value) {
+  /* package */ boolean onStringElement(int id, String value) {
     switch (id) {
       case ID_DOC_TYPE:
         // Validate that DocType is supported. This extractor only supports "webm".
@@ -282,8 +276,7 @@ public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandl
     return true;
   }
 
-  @Override
-  public boolean onBinaryElement(
+  /* package */ boolean onBinaryElement(
       int id, long elementOffsetBytes, int headerSizeBytes, int contentsSizeBytes,
       NonBlockingInputStream inputStream) {
     if (id == ID_SIMPLE_BLOCK) {
@@ -383,4 +376,52 @@ public final class DefaultWebmExtractor implements WebmExtractor, EbmlEventHandl
     prepared = true;
   }
 
+  /**
+   * Passes events through to {@link DefaultWebmExtractor} as
+   * callbacks from {@link EbmlReader} are received.
+   */
+  private final class InnerEbmlEventHandler implements EbmlEventHandler {
+
+    @Override
+    public int getElementType(int id) {
+      return DefaultWebmExtractor.this.getElementType(id);
+    }
+
+    @Override
+    public boolean onMasterElementStart(
+        int id, long elementOffsetBytes, int headerSizeBytes, long contentsSizeBytes) {
+      return DefaultWebmExtractor.this.onMasterElementStart(
+          id, elementOffsetBytes, headerSizeBytes, contentsSizeBytes);
+    }
+
+    @Override
+    public boolean onMasterElementEnd(int id) {
+      return DefaultWebmExtractor.this.onMasterElementEnd(id);
+    }
+
+    @Override
+    public boolean onIntegerElement(int id, long value) {
+      return DefaultWebmExtractor.this.onIntegerElement(id, value);
+    }
+
+    @Override
+    public boolean onFloatElement(int id, double value) {
+      return DefaultWebmExtractor.this.onFloatElement(id, value);
+    }
+
+    @Override
+    public boolean onStringElement(int id, String value) {
+      return DefaultWebmExtractor.this.onStringElement(id, value);
+    }
+
+    @Override
+    public boolean onBinaryElement(
+        int id, long elementOffsetBytes, int headerSizeBytes, int contentsSizeBytes,
+        NonBlockingInputStream inputStream) {
+      return DefaultWebmExtractor.this.onBinaryElement(
+          id, elementOffsetBytes, headerSizeBytes, contentsSizeBytes, inputStream);
+    }
+
+  }
+
 }
diff --git a/library/src/main/java/com/google/android/exoplayer/smoothstreaming/SmoothStreamingChunkSource.java b/library/src/main/java/com/google/android/exoplayer/smoothstreaming/SmoothStreamingChunkSource.java
index 6f2a2490a2..e8ed35d239 100644
--- a/library/src/main/java/com/google/android/exoplayer/smoothstreaming/SmoothStreamingChunkSource.java
+++ b/library/src/main/java/com/google/android/exoplayer/smoothstreaming/SmoothStreamingChunkSource.java
@@ -235,8 +235,8 @@ public class SmoothStreamingChunkSource implements ChunkSource {
     DataSpec dataSpec = new DataSpec(uri, offset, -1, cacheKey);
     // In SmoothStreaming each chunk contains sample timestamps relative to the start of the chunk.
     // To convert them the absolute timestamps, we need to set sampleOffsetUs to -chunkStartTimeUs.
-    return new Mp4MediaChunk(dataSource, dataSpec, formatInfo, trigger, extractor,
-        chunkStartTimeUs, nextStartTimeUs, -chunkStartTimeUs, nextChunkIndex);
+    return new Mp4MediaChunk(dataSource, dataSpec, formatInfo, trigger, chunkStartTimeUs,
+        nextStartTimeUs, nextChunkIndex, extractor, false, -chunkStartTimeUs);
   }
 
   private static byte[] getKeyId(byte[] initData) {