/// <summary>
/// Select the next media bit rate using the minimum value from
/// 2 criterias:
/// <para>
/// Condition 1) The bit rate selected must allow the buffer
/// fullness to grow at least N times faster than the measured
/// download bandwidth
/// </para>
/// <para>
/// Condition 2) Using a fraction of the current buffer
/// fullness, and a fraction of the past download bandwidth
/// (network bit rate), find the highest bit rate encoding at
/// which we can download to get as close as possible to the
/// current target speed content download
/// </para>
/// <para>
/// Condition 3) If in place, will not let the bit rate speed
/// change be larger than 1 step
/// </para>
/// <para>
/// NOTE speed content download is defined for a given stream
/// bit rate (actually the bytes size) and network bit rate,
/// as the amount of seconds worth of content that we can
/// download per wall clock second
/// </para>
/// </summary>
/// <param name="networkMediaInfo">the network media info to query</param>
/// <param name="chunkDuration">the duration of the last chunk</param>
/// <returns>the next bitrate to use</returns>
private ulong GetNextBitRateUsingBandwidth(NetworkMediaInfo networkMediaInfo, double chunkDuration)
{
// If we are using a locked bit rate then our job is easy
if (networkMediaInfo.LockedBitRate >= 0)
{
return networkMediaInfo.BitratesInfo[networkMediaInfo.LockedBitRate].NominalBitrate;
}
// Condition 1
ulong bitRateCond1 = (ulong)(networkMediaInfo.DownloadBandwidthWindow.CurrentKernel / networkMediaInfo.RelativeContentDownloadSpeed);
// Condition 2
ulong bitRateCond2 = (ulong)
(networkMediaInfo.DownloadBandwidthWindow.CurrentKernel
*
networkMediaInfo.BufferFullnessWindow.CurrentKernel
*
(sm_NetworkHeuristicsParams.DownloadBandwidthFraction *
sm_NetworkHeuristicsParams.BufferFullnessFraction /
chunkDuration));
ulong bitRateFinal =
bitRateCond2 < bitRateCond1 ? bitRateCond2 : bitRateCond1;
// Condition 3
ulong bitRateCond3 = ulong.MaxValue;
// Only limit bitrate changes to one step at
// a time (condition 3)
if (networkMediaInfo.IsLimitBitrateSteps == true)
{
int bitRateIndex = networkMediaInfo.FindBitRateIndex(networkMediaInfo.PreviousBitrate) + 1;
bitRateCond3 = networkMediaInfo.FindClosestBitrateByIndex(bitRateIndex);
if (bitRateCond3 < bitRateFinal)
{
bitRateFinal = bitRateCond3;
}
}
NhTrace("INFO", networkMediaInfo.StreamId, "C1({0}):{1} C2:{2} C3:{3} final:{4}", networkMediaInfo.RelativeContentDownloadSpeed, bitRateCond1, bitRateCond2, bitRateCond3, bitRateFinal);
return bitRateFinal;
}
/// <summary>
/// Return the bit rate 1 step above (step > 0) or 1 step
/// below (step less than 0) the current one
/// </summary>
/// <param name="networkMediaInfo">The nextwork media info to query</param>
/// <param name="step">Increse/decrease bit rate in "step" steps</param>
/// <returns>next bitrate, in bps</returns>
private static ulong GetNextBitRate(NetworkMediaInfo networkMediaInfo, int step)
{
if (networkMediaInfo.LockedBitRate >= 0)
{
return networkMediaInfo.BitratesInfo[networkMediaInfo.LockedBitRate].NominalBitrate;
}
int index = 0;
for (; index < networkMediaInfo.BitratesInfo.Length; index++)
{
if (networkMediaInfo.PreviousBitrate == networkMediaInfo.BitratesInfo[index].NominalBitrate)
{
break;
}
}
index += step;
return networkMediaInfo.FindClosestBitrateByIndex(index);
}
