/// <summary>
/// Creates a frame source object given the raw FFmpeg subtitle reference.
/// </summary>
/// <param name="frame">The raw FFmpeg subtitle pointer.</param>
/// <returns>The managed frame</returns>
protected override unsafe MediaFrame CreateFrameSource(AVSubtitle *frame)
{
var frameHolder = new SubtitleFrame(frame, this);
return(frameHolder);
}
/// <summary>
/// Receives 0 or more frames from the next available packet in the Queue.
/// This sends the first available packet to dequeue to the decoder
/// and uses the decoded frames (if any) to their corresponding
/// ProcessFrame method.
/// </summary>
/// <returns>The list of frames</returns>
private List <MediaFrame> DecodeNextPacketInternal()
{
var result = new List <MediaFrame>();
// Ensure there is at least one packet in the queue
if (PacketBufferCount <= 0)
{
return(result);
}
// Setup some initial state variables
var packet = Packets.Dequeue();
// The packets are alwasy sent. We dequeue them and keep a reference to them
// in the SentPackets queue
SentPackets.Push(packet);
var receiveFrameResult = 0;
if (MediaType == MediaType.Audio || MediaType == MediaType.Video)
{
// If it's audio or video, we use the new API and the decoded frames are stored in AVFrame
// Let us send the packet to the codec for decoding a frame of uncompressed data later
var sendPacketResult = ffmpeg.avcodec_send_packet(CodecContext, IsEmptyPacket(packet) ? null : packet);
// Let's check and see if we can get 1 or more frames from the packet we just sent to the decoder.
// Audio packets will typically contain 1 or more audioframes
// Video packets might require several packets to decode 1 frame
MediaFrame managedFrame = null;
while (receiveFrameResult == 0)
{
// Allocate a frame in unmanaged memory and
// Try to receive the decompressed frame data
var outputFrame = ffmpeg.av_frame_alloc();
RC.Current.Add(outputFrame, $"327: {nameof(MediaComponent)}[{MediaType}].{nameof(DecodeNextPacketInternal)}()");
receiveFrameResult = ffmpeg.avcodec_receive_frame(CodecContext, outputFrame);
try
{
managedFrame = null;
if (receiveFrameResult == 0)
{
// Send the frame to processing
managedFrame = CreateFrameSource(ref outputFrame);
if (managedFrame != null)
{
result.Add(managedFrame);
}
}
if (managedFrame == null)
{
RC.Current.Remove(outputFrame);
ffmpeg.av_frame_free(&outputFrame);
}
}
catch
{
// Release the frame as the decoded data could not be processed
RC.Current.Remove(outputFrame);
ffmpeg.av_frame_free(&outputFrame);
throw;
}
}
}
else if (MediaType == MediaType.Subtitle)
{
// Fors subtitles we use the old API (new API send_packet/receive_frame) is not yet available
var gotFrame = 0;
var outputFrame = SubtitleFrame.AllocateSubtitle();
receiveFrameResult = ffmpeg.avcodec_decode_subtitle2(CodecContext, outputFrame, &gotFrame, packet);
// Check if there is an error decoding the packet.
// If there is, remove the packet clear the sent packets
if (receiveFrameResult < 0)
{
SubtitleFrame.DeallocateSubtitle(outputFrame);
SentPackets.Clear();
Container.Logger?.Log(MediaLogMessageType.Error, $"{MediaType}: Error decoding. Error Code: {receiveFrameResult}");
}
else
{
// Process the first frame if we got it from the packet
// Note that there could be more frames (subtitles) in the packet
if (gotFrame != 0)
{
try
{
// Send the frame to processing
var managedFrame = CreateFrameSource(outputFrame);
if (managedFrame == null)
{
throw new MediaContainerException($"{MediaType} Component does not implement {nameof(CreateFrameSource)}");
}
result.Add(managedFrame);
}
catch
{
// Once processed, we don't need it anymore. Release it.
SubtitleFrame.DeallocateSubtitle(outputFrame);
throw;
}
}
// Let's check if we have more decoded frames from the same single packet
// Packets may contain more than 1 frame and the decoder is drained
// by passing an empty packet (data = null, size = 0)
while (gotFrame != 0 && receiveFrameResult > 0)
{
outputFrame = SubtitleFrame.AllocateSubtitle();
var emptyPacket = ffmpeg.av_packet_alloc();
RC.Current.Add(emptyPacket, $"406: {nameof(MediaComponent)}[{MediaType}].{nameof(DecodeNextPacketInternal)}()");
// Receive the frames in a loop
try
{
receiveFrameResult = ffmpeg.avcodec_decode_subtitle2(CodecContext, outputFrame, &gotFrame, emptyPacket);
if (gotFrame != 0 && receiveFrameResult > 0)
{
// Send the subtitle to processing
var managedFrame = CreateFrameSource(outputFrame);
if (managedFrame == null)
{
throw new MediaContainerException($"{MediaType} Component does not implement {nameof(CreateFrameSource)}");
}
result.Add(managedFrame);
}
}
catch
{
// once the subtitle is processed. Release it from memory
SubtitleFrame.DeallocateSubtitle(outputFrame);
throw;
}
finally
{
// free the empty packet
RC.Current.Remove(emptyPacket);
ffmpeg.av_packet_free(&emptyPacket);
}
}
}
}
// Release the sent packets if 1 or more frames were received in the packet
if (result.Count >= 1 || (Container.IsAtEndOfStream && IsEmptyPacket(packet) && PacketBufferCount == 0))
{
// We clear the sent packet queue (releasing packet from unmanaged memory also)
// because we got at least 1 frame from the packet.
SentPackets.Clear();
}
return(result);
}