Media Source Extensions

2.4.1 Attaching to a media element

A MediaSource object can be attached to a media element by assigning a MediaSource object URL to the media element src attribute or the src attribute of a <source> inside a media element. A MediaSource object URL is created by passing a MediaSource object to createObjectURL().

If the resource fetch algorithm absolute URL matches the MediaSource object URL, run the following steps right before the "Perform a potentially CORS-enabled fetch" step in the resource fetch algorithm.

If readyState is NOT set to "closed"

Run the steps of the resource fetch algorithm.

Otherwise

1. Set the readyState attribute to "open".
2. Queue a task to fire a simple event named sourceopen at the MediaSource.
3. Allow the resource fetch algorithm to progress based on data passed in via appendBuffer() and appendStream().

2.4.2 Detaching from a media element

The following steps are run in any case where the media element is going to transition to NETWORK_EMPTY and queue a task to fire a simple event named emptied at the media element. These steps should be run right before the transition.

1. Set the readyState attribute to "closed".
2. Set the duration attribute to NaN.
3. Remove all the SourceBuffer objects from activeSourceBuffers.
4. Queue a task to fire a simple event named removesourcebuffer at activeSourceBuffers.
5. Remove all the SourceBuffer objects from sourceBuffers.
6. Queue a task to fire a simple event named removesourcebuffer at sourceBuffers.
7. Queue a task to fire a simple event named sourceclose at the MediaSource.

2.4.3 Seeking

Run the following steps as part of the "Wait until the user agent has established whether or not the media data for the new playback position is available, and, if it is, until it has decoded enough data to play back that position" step of the seek algorithm:

1. The media element looks for media segments containing the new playback position in each SourceBuffer object in activeSourceBuffers.

   If one or more of the objects in activeSourceBuffers is missing media segments for the new playback position

   1. Set the HTMLMediaElement.readyState attribute to HAVE_METADATA.
   2. The media element waits for the necessary media segments to be passed to appendBuffer() or appendStream().
      Note

      The web application can use buffered to determine what the media element needs to resume playback.

   Otherwise

   Continue

2. The media element resets all decoders and initializes each one with data from the appropriate initialization segment.
3. The media element feeds data from the media segments into the decoders until the new playback position is reached.
4. Resume the seek algorithm at the "Await a stable state" step.

2.4.4 SourceBuffer Monitoring

The following steps are periodically run during playback to make sure that all of the SourceBuffer objects in activeSourceBuffers have enough data to ensure uninterrupted playback. Appending new segments and changes to activeSourceBuffers also cause these steps to run because they affect the conditions that trigger state transitions.

Having enough data to ensure uninterrupted playback is an implementation specific condition where the user agent determines that it currently has enough data to play the presentation without stalling for a meaningful period of time. This condition is constantly evaluated to determine when to transition the media element into and out of the HAVE_ENOUGH_DATA ready state. These transitions indicate when the user agent believes it has enough data buffered or it needs more data respectively.

If buffered for all objects in activeSourceBuffers do not contain TimeRanges for the current playback position:

1. Set the HTMLMediaElement.readyState attribute to HAVE_METADATA.
2. If this is the first transition to HAVE_METADATA, then queue a task to fire a simple event named loadedmetadata at the media element.
3. Abort these steps.

If buffered for all objects in activeSourceBuffers contain TimeRanges that include the current playback position and enough data to ensure uninterrupted playback:

1. Set the HTMLMediaElement.readyState attribute to HAVE_ENOUGH_DATA.
2. Queue a task to fire a simple event named canplaythrough at the media element.
3. Playback may resume at this point if it was previously suspended by a transition to HAVE_CURRENT_DATA.
4. Abort these steps.

If buffered for at least one object in activeSourceBuffers contains a TimeRange that includes the current playback position but not enough data to ensure uninterrupted playback:

1. Set the HTMLMediaElement.readyState attribute to HAVE_FUTURE_DATA.
2. If the previous value of HTMLMediaElement.readyState was less than HAVE_FUTURE_DATA, then queue a task to fire a simple event named canplay at the media element.
3. Playback may resume at this point if it was previously suspended by a transition to HAVE_CURRENT_DATA.
4. Abort these steps.

If buffered for at least one object in activeSourceBuffers contains a TimeRange that ends at the current playback position and does not have a range covering the time immediately after the current position:

1. Set the HTMLMediaElement.readyState attribute to HAVE_CURRENT_DATA.
2. If this is the first transition to HAVE_CURRENT_DATA, then queue a task to fire a simple event named loadeddata at the media element.
3. Playback is suspended at this point since the media element doesn't have enough data to advance the timeline.
4. Abort these steps.

2.4.5 Changes to selected/enabled track state

During playback activeSourceBuffers needs to be updated if the selected video track, the enabled audio tracks, or a text track mode changes. When one or more of these changes occur the following steps need to be followed.

If the selected video track changes, then run the following steps:

1. If the SourceBuffer associated with the previously selected video track is not associated with any other enabled tracks, run the following steps:
   1. Remove the SourceBuffer from activeSourceBuffers.
   2. Queue a task to fire a simple event named removesourcebuffer at activeSourceBuffers
2. If the SourceBuffer associated with the newly selected video track is not already in activeSourceBuffers, run the following steps:
   1. Add the SourceBuffer to activeSourceBuffers.
   2. Queue a task to fire a simple event named addsourcebuffer at activeSourceBuffers

If an audio track becomes disabled and the SourceBuffer associated with this track is not associated with any other enabled or selected track, then run the following steps:

1. Remove the SourceBuffer associated with the audio track from activeSourceBuffers
2. Queue a task to fire a simple event named removesourcebuffer at activeSourceBuffers

If an audio track becomes enabled and the SourceBuffer associated with this track is not already in activeSourceBuffers, then run the following steps:

1. Add the SourceBuffer associated with the audio track to activeSourceBuffers
2. Queue a task to fire a simple event named addsourcebuffer at activeSourceBuffers

If a text track mode becomes "disabled" and the SourceBuffer associated with this track is not associated with any other enabled or selected track, then run the following steps:

1. Remove the SourceBuffer associated with the text track from activeSourceBuffers
2. Queue a task to fire a simple event named removesourcebuffer at activeSourceBuffers

If a text track mode becomes "showing" or "hidden" and the SourceBuffer associated with this track is not already in activeSourceBuffers, then run the following steps:

1. Add the SourceBuffer associated with the text track to activeSourceBuffers
2. Queue a task to fire a simple event named addsourcebuffer at activeSourceBuffers

2.4.6 Duration change

Follow these steps when duration needs to change to a new duration.

1. If the current value of duration is equal to new duration, then abort these steps.
2. Set old duration to the current value of duration.
3. Update duration to new duration.
4. If the new duration is less than old duration, then call remove(new duration, old duration) on all objects in sourceBuffers.
   Note

   This preserves audio frames that start before and end after the duration. The user agent must end playback at duration even if the audio frame extends beyond this time.

5. Update the media controller duration to new duration and run the HTMLMediaElement duration change algorithm.

3.5.1 Segment Parser Loop

All SourceBuffer objects have an internal append state variable that keeps track of the high-level segment parsing state. It is initially set to WAITING_FOR_SEGMENT and can transition to the following states as data is appended.

The input buffer is a byte buffer that is used to hold unparsed bytes across appendBuffer() and appendStream() calls. The buffer is empty when the SourceBuffer object is created.

The buffer full flag keeps track of whether appendBuffer() or appendStream() is allowed to accept more bytes. It is set to false when the SourceBuffer object is created and gets updated as data is appended and removed.

The abort mode variable keeps track of the AbortMode passed to the last abort() call. It is unset when the SourceBuffer object is created and gets updated by abort() and the coded frame processing algorithm.

The continuation timestamp variable keeps track of the start timestamp for the next append sequence if abort() is called with "continuation". It is unset when the SourceBuffer object is created and gets updated by abort() and the coded frame processing algorithm.

The highest presentation end timestamp variable stores the highest presentation end timestamp encountered in the current append sequence. It is unset when the SourceBuffer object is created and gets updated by the reset parser state algorithm and the coded frame processing algorithm.

When this algorithm is invoked, run the following steps:

1. Loop Top: If the input buffer is empty, then jump to the need more data step below.
2. If the input buffer starts with bytes that violate the byte stream format specifications, then run the append error algorithm and abort this algorithm.
3. Remove any bytes that the byte stream format specifications say should be ignored from the start of the input buffer.

4. If the append state equals WAITING_FOR_SEGMENT, then run the following steps:

   1. If the beginning of the input buffer indicates the start of an initialization segment, set the append state to PARSING_INIT_SEGMENT.
   2. If the beginning of the input buffer indicates the start of an media segment, set append state to PARSING_MEDIA_SEGMENT.
   3. Jump to the loop top step above.

5. If the append state equals PARSING_INIT_SEGMENT, then run the following steps:

   1. If the input buffer does not contain a complete initialization segment yet, then jump to the need more data step below.
   2. Run the initialization segment received algorithm.
   3. Remove the initialization segment bytes from the beginning of the input buffer.
   4. Set append state to WAITING_FOR_SEGMENT.
   5. Jump to the loop top step above.

6. If the append state equals PARSING_MEDIA_SEGMENT, then run the following steps:

   1. If the first initialization segment flag is false, then run the append error algorithm and abort this algorithm.

   2. If the input buffer does not contain a complete media segment header yet, then jump to the need more data step below.

      Note

      Implementations may choose to implement this state as an incremental parser so that it is not necessary to have the entire media segment before running the coded frame processing algorithm.

   3. Run the coded frame processing algorithm.
   4. Remove the media segment bytes from the beginning of the input buffer.
   5. If this SourceBuffer is full and cannot accept more media data, then set the buffer full flag to true.

   6. Set append state to WAITING_FOR_SEGMENT.

      Note

      Incremental parsers should only do this transition after the entire media segment has been received.

   7. Jump to the loop top step above.
7. Need more data: Return control to the calling algorithm.

3.5.2 Reset Parser State

When the parser state needs to be reset, run the following steps:

1. If the append state equals PARSING_MEDIA_SEGMENT and the input buffer contains some complete coded frames, then run the coded frame processing algorithm as if the media segment only contained these frames.
2. Unset the last decode timestamp on all track buffers.
3. Unset the highest presentation timestamp on all track buffers.
4. Unset the highest presentation end timestamp.
5. Set the need random access point flag on all track buffers to true.
6. Remove all bytes from the input buffer.
7. Set append state to WAITING_FOR_SEGMENT.

3.5.3 Append Error

When an error occurs during an append, run the following steps:

1. Run the reset parser state algorithm.
2. Abort the stream append loop algorithm if it is running.
3. Set the updating attribute to false.
4. Queue a task to fire a simple event named error at this SourceBuffer object.
   Issue 1

   Need a way to convey error information.

5. Queue a task to fire a simple event named updateend at this SourceBuffer object.

3.5.4 Stream Append Loop

When a Stream is passed to appendStream(), the following steps are run to transfer data from the Stream to the SourceBuffer. This algorithm is initialized with the stream and maxSize parameters from the appendStream() call.

1. If maxSize is set, then let bytesLeft equal maxSize.
2. Loop Top: If maxSize is set and bytesLeft equals 0, then jump to the loop done step below.
3. If stream has been closed, then jump to the loop done step below.

4. If the buffer full flag equals true, then run the append error algorithm and abort this algorithm.

   Note

   The web application must use remove() to free up space in the SourceBuffer.

5. Read data from stream into data:

   If maxSize is set:

   1. Read up to bytesLeft bytes from stream into data.
   2. Subtract the number of bytes in data from bytesLeft.

   Otherwise:

   Read all available bytes in stream into data.

6. If an error occured while reading from stream, then run the append error algorithm and abort this algorithm.
7. Add data to the end of the input buffer.
8. Run the segment parser loop algorithm.
9. Jump to the loop top step above.
10. Loop Done: Set the updating attribute to false.
11. Queue a task to fire a simple event named update at this SourceBuffer object.
12. Queue a task to fire a simple event named updateend at this SourceBuffer object.

3.5.5 Initialization Segment Received

The following steps are run when the segment parser loop successfully parses a complete initialization segment:

Each SourceBuffer object has an internal first initialization segment flag that tracks whether the first initialization segment has been appended. This flag is set to false when the SourceBuffer is created and updated by the algorithm below.

1. Update the duration attribute if it currently equals NaN:

   If the initialization segment contains a duration:

   Run the duration change algorithm with new duration set to the duration in the initialization segment.

   Otherwise:

   Run the duration change algorithm with new duration set to positive Infinity.

2. If the initialization segment has no audio, video, or text tracks, then call endOfStream("decode") and abort these steps.
3. If the first initialization segment flag is true, then run the following steps:
   1. Verify the following properties. If any of the checks fail then call endOfStream("decode") and abort these steps.
      • The number of audio, video, and text tracks match what was in the first initialization segment.
      • The codecs for each track, match what was specified in the first initialization segment.
      • If more than one track for a single type are present (ie 2 audio tracks), then the Track IDs match the ones in the first initialization segment.
   2. Add the appropriate track descriptions from this initialization segment to each of the track buffers.
4. Let active track flag equal false.

5. If the first initialization segment flag is false, then run the following steps:

   1. For each audio track in the initialization segment, run following steps:

      1. Let new audio track be a new AudioTrack object.
      2. Generate a unique ID and assign it to the id property on new audio track.

      3. If audioTracks.length equals 0, then run the following steps:

         1. Set the enabled property on new audio track to true.
         2. Set active track flag to true.
      4. Add new audio track to the audioTracks attribute on this SourceBuffer object.
      5. Queue a task to fire a simple event named addtrack at audioTracks attribute on this SourceBuffer object.
      6. Add new audio track to the audioTracks attribute on the HTMLMediaElement.
      7. Queue a task to fire a simple event named addtrack at the audioTracks attribute on the HTMLMediaElement.
      8. Create a new track buffer to store coded frames for this track.
      9. Add the track description for this track to the track buffer.

   2. For each video track in the initialization segment, run following steps:

      1. Let new video track be a new VideoTrack object.
      2. Generate a unique ID and assign it to the id property on new video track.

      3. If videoTracks.length equals 0, then run the following steps:

         1. Set the selected property on new video track to true.
         2. Set active track flag to true.
      4. Add new video track to the videoTracks attribute on this SourceBuffer object.
      5. Queue a task to fire a simple event named addtrack at videoTracks attribute on this SourceBuffer object.
      6. Add new video track to the videoTracks attribute on the HTMLMediaElement.
      7. Queue a task to fire a simple event named addtrack at the videoTracks attribute on the HTMLMediaElement.
      8. Create a new track buffer to store coded frames for this track.
      9. Add the track description for this track to the track buffer.

   3. For each text track in the initialization segment, run following steps:

      1. Let new text track be a new TextTrack object with its properties populated with the appropriate information from the initialization segment.
      2. If the mode property on new text track equals "showing" or "hidden", then set active track flag to true.
      3. Add new text track to the textTracks attribute on this SourceBuffer object.
      4. Queue a task to fire a simple event named addtrack at textTracks attribute on this SourceBuffer object.
      5. Add new text track to the textTracks attribute on the HTMLMediaElement.
      6. Queue a task to fire a simple event named addtrack at the textTracks attribute on the HTMLMediaElement.
      7. Create a new track buffer to store coded frames for this track.
      8. Add the track description for this track to the track buffer.
   4. If active track flag equals true, then run the following steps:
      1. Add this SourceBuffer to activeSourceBuffers.
      2. Queue a task to fire a simple event named addsourcebuffer at activeSourceBuffers
   5. Set first initialization segment flag to true.

6. If the HTMLMediaElement.readyState attribute is HAVE_NOTHING, then run the following steps:

   1. If one or more objects in sourceBuffers have first initialization segment flag set to false, then abort these steps.
   2. Set the HTMLMediaElement.readyState attribute to HAVE_METADATA.
   3. Queue a task to fire a simple event named loadedmetadata at the media element.
7. If the active track flag equals true and the HTMLMediaElement.readyState attribute is greater than HAVE_CURRENT_DATA, then set the HTMLMediaElement.readyState attribute to HAVE_METADATA.

3.5.6 Coded Frame Processing

When complete coded frames have been parsed by the segment parser loop then the following steps are run:

1. For each coded frame in the media segment run the following steps:

   1. Let presentation timestamp be a double precision floating point representation of the coded frame's presentation timestamp in seconds.
   2. Let decode timestamp be a double precision floating point representation of the coded frame's decode timestamp in seconds.
      Note

      Implementations don't have to internally store timestamps in a double precision floating point representation. This representation is used here because it is the represention for timestamps in the HTML spec. The intention here is to make the behavior clear without adding unnecessary complexity to the algorithm to deal with the fact that adding a timestampOffset may cause a timestamp rollover in the underlying timestamp representation used by the bytestream format. Implementations can use any internal timestamp representation they wish, but the addition of timestampOffset should behave in a similar manner to what would happen if a double precision floating point representation was used.

   3. Let frame duration be a double precision floating point representation of the coded frame's duration in seconds.
   4. If abort mode is set, then run the following steps:

      1. If abort mode equals "continuation":

         Set timestampOffset equal to continuation timestamp - presentation timestamp.

         If abort mode equals "timestampOffset":

         1. Let old timestampOffset equal the current value of timestampOffset.
         2. Set timestampOffset equal to old timestampOffset - presentation timestamp.

      2. Unset continuation timestamp.
      3. Unset abort mode.

   5. If timestampOffset is not 0, then run the following steps:

      1. Add timestampOffset to the presentation timestamp.
      2. Add timestampOffset to the decode timestamp.
      3. If the presentation timestamp or decode timestamp is less than the presentation start time, then call endOfStream("decode"), and abort these steps.
   6. Let track buffer equal the track buffer that the coded frame should be added to.
   7. If last decode timestamp for track buffer is set and decode timestamp is less than last decode timestamp or the difference between decode timestamp and last decode timestamp is greater than 100 milliseconds, then call endOfStream("decode") and abort these steps.
      Note

      These checks trigger an error when the application attempts out-of-order appends without an intervening abort().

   8. Let frame end timestamp equal the sum of presentation timestamp and frame duration.
   9. If the need random access point flag on track buffer equals true, then run the following steps:
      1. If the coded frame is not a random access point, then drop the coded frame and jump to the top of the loop to start processing the next coded frame.
      2. Set the need random access point flag on track buffer to false.
   10. Let spliced frame be an unset variable for holding audio splice information
   11. If last decode timestamp for track buffer is unset and presentation timestamp lies within a coded frame already stored in track buffer, then run the following steps:
       1. Let overlapped frame be the coded frame in track buffer that contains presentation timestamp.
       2. If track buffer contains audio coded frames, then run the audio splice frame algorithm and if a splice frame is returned, assign it to spliced frame.
       3. If track buffer contains video coded frames and presentation timestamp is less than 1 microsecond beyond the presentation timestamp of overlapped frame, then remove overlapped frame and any coded frames that depend on it from track buffer.
          Note

          This is to compensate for minor errors in frame timestamp computations that can appear when converting back and forth between double precision floating point numbers and rationals. This tolerance allows a frame to replace an existing one as long as it is within 1 microsecond of the existing frame's start time. Frames that come slightly before an existing frame are handled by the removal step below.

   12. Remove existing coded frames in track buffer:

       If highest presentation timestamp for track buffer is not set:

       Remove all coded frames from track buffer that have a presentation timestamp greater than or equal to presentation timestamp and less than frame end timestamp.

       If highest presentation timestamp for track buffer is set and less than presentation timestamp

       Remove all coded frames from track buffer that have a presentation timestamp greater than highest presentation timestamp and less than or equal to frame end timestamp.

   13. Remove all coded frames from track buffer that have decoding dependencies on the coded frames removed in the previous step.
       Note

       For example if an I-frame is removed in the previous step, then all P-frames & B-frames that depend on that I-frame should be removed from track buffer. This makes sure that decode dependencies are properly maintained during overlaps.

   14. If spliced frame is set:

       Add spliced frame to the track buffer.

       Otherwise:

       Add the coded frame with the presentation timestamp, decode timestamp, and frame duration to the track buffer.

   15. Set last decode timestamp for track buffer to decode timestamp.
   16. If highest presentation timestamp for track buffer is unset or frame end timestamp is greater than highest presentation timestamp, then set highest presentation timestamp for track buffer to frame end timestamp.
       Note

       The greater than check is needed because bidirectional prediction between coded frames can cause presentation timestamp to not be monotonically increasing eventhough the decode timestamps are monotonically increasing.

   17. If highest presentation end timestamp is unset or frame end timestamp is greater than highest presentation end timestamp, then set highest presentation end timestamp equal to frame end timestamp.

2. If the HTMLMediaElement.readyState attribute is HAVE_METADATA and the new coded frames cause all objects in activeSourceBuffers to have media data for the current playback position, then run the following steps:

   1. Set the HTMLMediaElement.readyState attribute to HAVE_CURRENT_DATA.
   2. If this is the first transition to HAVE_CURRENT_DATA, then queue a task to fire a simple event named loadeddata at the media element.

3. If the HTMLMediaElement.readyState attribute is HAVE_CURRENT_DATA and the new coded frames cause all objects in activeSourceBuffers to have media data beyond the current playback position, then run the following steps:

   1. Set the HTMLMediaElement.readyState attribute to HAVE_FUTURE_DATA.
   2. Queue a task to fire a simple event named canplay at the media element.

4. If the HTMLMediaElement.readyState attribute is HAVE_FUTURE_DATA and the new coded frames cause all objects in activeSourceBuffers to have enough data to ensure uninterrupted playback, then run the following steps:

   1. Set the HTMLMediaElement.readyState attribute to HAVE_ENOUGH_DATA.
   2. Queue a task to fire a simple event named canplaythrough at the media element.
5. If the media segment contains data beyond the current duration, then run the duration change algorithm with new duration set to the maximum of the current duration and the highest end timestamp reported by HTMLMediaElement.buffered.

3.5.7 Audio Splice Frame Algorithm

Follow these steps when the coded frame processing algorithm needs to generate a splice frame for two overlapping audio coded frames:

1. Let track buffer be the track buffer that will contain the splice.
2. Let new coded frame be the new coded frame, that is being added to track buffer, which triggered the need for a splice.
3. Let presentation timestamp be the presentation timestamp for new coded frame
4. Let decode timestamp be the decode timestamp for new coded frame.
5. Let frame duration be the duration of new coded frame.
6. Let overlapped frame be the coded frame in track buffer that overlaps with new coded frame (ie. it contains presentation timestamp).
7. Round & update presentation timestamp and decode timestamp to the nearest audio sample timestamp based on sample rate of the audio in overlapped frame.
   Note

   For example, given the following values:

   • The presentation timestamp of overlapped frame equals 10.
   • The sample rate of overlapped frame equals 8000 Hz
   • presentation timestamp equals 10.01255
   • decode timestamp equals 10.01255

   presentation timestamp and decode timestamp are rounded & updated to 10.0125 since 10.01255 is closer to 10 + 100/8000 (10.0125) than 10 + 101/8000 (10.012625)

8. If the user agent does not support crossfading then run the following steps:
   1. Remove overlapped frame from track buffer.
   2. Add a silence frame to track buffer with the following properties:
      • The presentation time set to the overlapped frame presentation time.
      • The decode time set to the overlapped frame decode time.
      • The frame duration set to difference between presentation timestamp and the overlapped frame presentation time.
   3. Return to caller without providing a splice frame.
      Note

      This is intended to allow new coded frame to be added to the track buffer as if overlapped frame had not been in the track buffer to begin with.

9. Let frame end timestamp equal the sum of presentation timestamp and frame duration.
10. Let fade out coded frames equal overlapped frame as well as any addition frames in track buffer that overlap presentation timestamp plus the splice duration of 5 milliseconds.
11. Remove all the frames included in fade out coded frames from track buffer.
12. Return a splice frame with the following properties:
    • The presentation time set to the overlapped frame presentation time.
    • The decode time set to the overlapped frame decode time.
    • The frame duration set to difference between frame end timestamp and the overlapped frame presentation time.
    • The fade out coded frames equals fade-out coded frames.
    • The fade in coded frame equals new coded frame.
    • The splice timestamp equals presentation timestamp.
    Note

    See the audio splice rendering algorithm for details on how this splice frame is rendered.

3.5.8 Audio Splice Rendering Algorithm

The following steps are run when a spliced frame, generated by the audio splice frame algorithm, needs to be rendered by the media element:

1. Let fade out coded frames be the coded frames that are faded out during the splice.
2. Let fade in coded frames be the coded frames that are faded in during the splice.
3. Let presentation timestamp be the presentation timestamp of the first coded frame in fade out coded frames.
4. Let end timestamp be the sum of the presentation timestamp and frame duration in the last frame in fade in coded frames.
5. Let splice timestamp be the presentation timestamp where the splice starts. This corresponds with the presentation timestamp of the first frame in fade in coded frames.
6. Let splice end timestamp equal splice timestamp plus five milliseconds.
7. Let fade out samples be the samples generated by decoding fade out coded frames.
8. Trim fade out samples so that it only contains samples between presentation timestamp and splice end timestamp.
9. Let fade in samples be the samples generated by decoding fade in coded frames.
10. Convert fade out samples and fade in samples to a common sample rate and channel layout.
11. Let output samples be a buffer to hold the output samples.
12. Apply a linear gain fade out to the samples between splice timestamp and splice end timestamp in fade out samples.
13. Apply a linear gain fade in to the samples between splice timestamp and splice end timestamp in fade in samples.
14. Copy samples between presentation timestamp to splice timestamp from fade out samples into output samples.
15. For each sample between splice timestamp and splice end timestamp, compute the sum of a sample from fade out samples and the corresponding sample in fade in samples and store the result in output samples.
16. Copy samples between splice end timestamp to end timestamp from fade in samples into output samples.
17. Render output samples.

Note

Here is a graphical representation of this algorithm.