protected FilePosition GetFilePosition(double searchOffset, AsfStreamType streamType, bool isStart)
{
FilePosition requestedPosition = new FilePosition(FileName, StartTimeOffsetVideo, 0, MediaType, (int)(searchOffset * 1000));
bool found = false;
bool isKeyframe = false;
bool wasKeyFrame = false;
long maxOffset = 0;
long minOffset = 0;
UInt32 startTimeOffset = requestedPosition.TimeOffset;
int diff = requestedPosition.Delta;
int prevDiff = 0;
FileStream fs = null;
long fileOffset = 0;
uint targetTimeOffset;
string fileName = requestedPosition.FileName;
AsfFileConfiguration asfConfig = _asfConfig;
uint TargetStreamId = streamType == AsfStreamType.asfAudio ? _asfConfig.AsfAudioStreamId : _asfConfig.AsfVideoStreamId;
UInt32 finalTimeOffset = (UInt32)Math.Max(0, startTimeOffset + diff);
targetTimeOffset = finalTimeOffset;
UInt32 maxTimeDifference = streamType == AsfStreamType.asfAudio ? AsfConstants.ASF_TIME_THRESHOLD_START_AUDIO : AsfConstants.ASF_TIME_THRESHOLD;
uint averagePacketDuration = GetAveragePacketDuration();
minOffset = asfConfig.AsfHeaderSize;
//set maxOffset to start of last packet
maxOffset = asfConfig.AsfHeaderSize + (asfConfig.AsfPacketCount - 1) * asfConfig.AsfPacketSize;
long packetCount = asfConfig.AsfPacketCount;
// open the file
try
{
fs = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
}
catch (Exception) { return(null); }
int prevPacketJumpCount = 0;
bool wasBroadSearch = false;
int totalJumpCount = 0;
int packetJumpCount = 0;
long searchMaxOffset = maxOffset;
long searchMinOffset = minOffset;
fileOffset = minOffset;
while (!found)
{
totalJumpCount++;
if (totalJumpCount > 500) //totally arbitrary number after which to give up
{
return(null);
}
packetJumpCount = (int)Math.Round((float)diff / averagePacketDuration);
if (Math.Abs(packetJumpCount) >= Math.Abs(prevPacketJumpCount) && Math.Abs(prevPacketJumpCount) > 0)
{ //we have to make sure that we converge, for this reason the number of packets we jump has to decrease at every iteration
if (Math.Abs(prevPacketJumpCount) > 1)
{
packetJumpCount = packetJumpCount > 0 ? Math.Abs(prevPacketJumpCount) - 1 : -Math.Abs(prevPacketJumpCount) + 1;
}
else
{
packetJumpCount = packetJumpCount > 0 ? 1 : -1;
}
}
prevPacketJumpCount = packetJumpCount;
long byteJump = asfConfig.AsfPacketSize * packetJumpCount;
if (fileOffset + byteJump > maxOffset)
{
byteJump = maxOffset - fileOffset;
packetJumpCount = (int)(byteJump / asfConfig.AsfPacketSize);
prevPacketJumpCount = packetJumpCount;
}
else if (fileOffset + byteJump < minOffset)
{
byteJump = minOffset - fileOffset;
packetJumpCount = (int)(byteJump / asfConfig.AsfPacketSize);
prevPacketJumpCount = packetJumpCount;
}
if (fs.Seek(fileOffset + byteJump, SeekOrigin.Begin) != fileOffset + byteJump)
{
return(null);
}
fileOffset += byteJump;
//track backwards if we cannot find target stream in this packet
while (!FindNextTimeOffset(asfConfig, fs, out isKeyframe, ref startTimeOffset, TargetStreamId))
{
fileOffset -= asfConfig.AsfPacketSize;
if (fs.Seek(fileOffset, SeekOrigin.Begin) != fileOffset)
{
return(null);
}
}
diff = (int)((long)finalTimeOffset - (long)startTimeOffset);
if (Math.Abs(diff) <= maxTimeDifference)
{
found = true;
if (isStart)
{
string.Format("Found video match at offset: {0} bytes, delta = {1} ms", fileOffset, diff).Log(LogLevel.logDetail);
}
}
else
{ //handle case of multiple frames in packet, return the packet right after target time since we will track back to previous keyframe anyway
if (diff > 0 && prevDiff < 0 && Math.Abs(packetJumpCount) == 1 && !wasBroadSearch)
{
found = true;
if (isStart)
{
string.Format("Found video match at offset: {0} bytes, delta = {1} ms", fileOffset, diff).Log(LogLevel.logDetail);
}
}
wasBroadSearch = false;
}
prevDiff = diff;
}
if (found && !isStart)
{
bool foundAudio = false;
bool temp;
//keep moving forward until we are PAST the requested end time or reach the end of the current asset
while ((!foundAudio || (foundAudio && diff > 0)) && fileOffset <= maxOffset)
{
if (fileOffset <= maxOffset)
{
if (fs.Seek(fileOffset + asfConfig.AsfPacketSize, SeekOrigin.Begin) != fileOffset + asfConfig.AsfPacketSize)
{
break;
}
foundAudio = FindNextTimeOffset(asfConfig, fs, out temp, ref startTimeOffset, asfConfig.AsfAudioStreamId, false);
fileOffset += asfConfig.AsfPacketSize;
}
//calculate again
if (foundAudio)
{
diff = (int)((long)finalTimeOffset - (long)startTimeOffset);
targetTimeOffset = startTimeOffset;
}
}
}
else if (found && isStart)
{
//now we have to find the previous keyframe, which also might be in the previous file if any exists
//even if current frame is a keyframe we have to go back if the keyframe is after the match time so the correct still frame is shown in all cases
//save the presentation Time of the match though, this time all earlier packets will be set to before preroll, so the
//stream "fast forwards" until the match time
targetTimeOffset = finalTimeOffset;
if (streamType == AsfStreamType.asfAudio)
{
wasKeyFrame = true; // Every packet in audio is a keyframe.
isKeyframe = true;
}
else //Video
{
wasKeyFrame = isKeyframe;
isKeyframe = false; //always go back to the previous key frame if possible to avoid edge condition with multiple frames in the same packet
}
while (((streamType != AsfStreamType.asfAudio && !isKeyframe) || diff < 0) && fileOffset > minOffset)
{
fileOffset -= asfConfig.AsfPacketSize;
if (fileOffset >= asfConfig.AsfHeaderSize)
{
fs.Seek(fileOffset, SeekOrigin.Begin);
FindNextTimeOffset(asfConfig, fs, out isKeyframe, ref startTimeOffset, TargetStreamId);
diff = (int)((long)finalTimeOffset - (long)startTimeOffset);
}
else
{
fileOffset = minOffset;
fs.Dispose();
//cannot find any earlier keyframe, just return position/file as is
if (found && wasKeyFrame)
{
return(new FilePosition(fileName, targetTimeOffset, fileOffset, requestedPosition.MediaType, diff));
}
else
{
return(null);
}
}
} //while
//calculate again
diff = (int)((long)finalTimeOffset - (long)startTimeOffset);
string.Format("Found keyframe at offset : {0} ms, delta = {1} ms", startTimeOffset, diff).Log(LogLevel.logDetail);
}
if (!isStart && fileOffset <= maxOffset)
{
fileOffset += asfConfig.AsfPacketSize; //include current packet
}
fs.Dispose();
if (found)
{
return(new FilePosition(fileName, targetTimeOffset, fileOffset, requestedPosition.MediaType, diff));
}
else
{
return(null); //cannot find any earlier keyframe, just return position/file as is
}
}
internal bool SetOffsetRange(double startOffset, double endOffset, out FilePosition requestStartPosition, out FilePosition requestEndPosition, AsfStreamType streamType)
{
requestStartPosition = null;
requestEndPosition = null;
// find the file and offset for the starting time
requestStartPosition = GetFilePosition(startOffset, streamType, true);
if (requestStartPosition == null)
{
return(false);
}
if (endOffset == 0)
{
long endFileOffset = EndOffset;
requestEndPosition = new FilePosition(requestStartPosition.FileName, uint.MaxValue, endFileOffset);
}
else
{
// find the file and offset for the ending time
requestEndPosition = GetFilePosition(endOffset, streamType, false);
if (requestEndPosition == null)
{
return(false);
}
}
StartOffset = requestStartPosition.FileOffset;
EndOffset = requestEndPosition.FileOffset;
Length = Convert.ToUInt32(EndOffset - StartOffset);
if (_fileStream != null)
{
_fileStream.Dispose();
}
_fileStream = null;
return(true);
}