size_t GetSeekablePacketNumber(FFMS_Track const& Frames, size_t PacketNumber) {
// Packets don't always have unique PTSes, so we may not be able to
// uniquely identify the packet we want. This function attempts to find
// a PTS we can seek to which will let us figure out which packet we're
// on before we get to the packet we actually wanted
// MatroskaAudioSource doesn't need this, as it seeks by byte offset
// rather than PTS. LAVF theoretically can seek by byte offset, but we
// don't use it as not all demuxers support it and it's broken in some of
// those that claim to support it
// However much we might wish to, we can't seek to before packet zero
if (PacketNumber == 0) return PacketNumber;
// Desired packet's PTS is unique, so don't do anything
if (Frames[PacketNumber].PTS != Frames[PacketNumber - 1].PTS &&
(PacketNumber + 1 == Frames.size() || Frames[PacketNumber].PTS != Frames[PacketNumber + 1].PTS))
return PacketNumber;
// When decoding, we only reliably know what packet we're at when the
// newly parsed packet has a different PTS from the previous one. As such,
// we walk backwards until we hit a different PTS and then seek to there,
// so that we can then decode until we hit the PTS group we actually wanted
// (and thereby know that we're at the first packet in the group rather
// than whatever the splitter happened to choose)
// This doesn't work if our desired packet has the same PTS as the first
// packet, but this scenario should never come up anyway; we permanently
// cache the decoded results from those packets, so there's no need to ever
// seek to them
int64_t PTS = Frames[PacketNumber].PTS;
while (PacketNumber > 0 && PTS == Frames[PacketNumber].PTS)
--PacketNumber;
return PacketNumber;
}
void FillAP(FFMS_AudioProperties &AP, AVCodecContext *CTX, FFMS_Track &Frames) {
AP.SampleFormat = static_cast<FFMS_SampleFormat>(CTX->sample_fmt);
AP.BitsPerSample = av_get_bytes_per_sample(CTX->sample_fmt) * 8;
AP.Channels = CTX->channels;;
AP.ChannelLayout = CTX->channel_layout;
AP.SampleRate = CTX->sample_rate;
if (Frames.size() > 0) {
AP.NumSamples = (Frames.back()).SampleStart + (Frames.back()).SampleCount;
AP.FirstTime = ((Frames.front().PTS * Frames.TB.Num) / (double)Frames.TB.Den) / 1000;
AP.LastTime = ((Frames.back().PTS * Frames.TB.Num) / (double)Frames.TB.Den) / 1000;
}
}