void FFMS_AudioSource::CacheBeginning() {
// Nothing to do if the cache is already populated
if (!Cache.empty()) return;
// The first frame is already decoded, so add it to the cache
CacheIterator it = Cache.end();
CacheBlock(it);
// The first packet after a seek is often decoded incorrectly, which
// makes it impossible to ever correctly seek back to the beginning, so
// store the first block now
// In addition, anything with the same PTS as the first packet can't be
// distinguished from the first packet and so can't be seeked to, so
// store those as well
// Some of LAVF's splitters don't like to seek to the beginning of the
// file (ts and?), so cache a few blocks even if PTSes are unique
// Packet 7 is the last packet I've had be unseekable to, so cache up to
// 10 for a bit of an extra buffer
CacheIterator end = Cache.end();
while (PacketNumber < Frames.size() &&
((Frames[0].PTS != ffms_av_nopts_value && Frames[PacketNumber].PTS == Frames[0].PTS) ||
Cache.size() < 10)) {
// Vorbis in particular seems to like having 60+ packets at the start
// of the file with a PTS of 0, so we might need to expand the search
// range to account for that.
// Expanding slightly before it's strictly needed to ensure there's a
// bit of space for an actual cache
if (Cache.size() >= MaxCacheBlocks - 5) {
if (MaxCacheBlocks >= EXCESSIVE_CACHE_SIZE)
throw FFMS_Exception(FFMS_ERROR_DECODING, FFMS_ERROR_ALLOCATION_FAILED,
"Exceeded the search range for an initial valid audio PTS");
MaxCacheBlocks *= 2;
}
DecodeNextBlock(&end);
}
// Store the iterator to the last element of the cache which is used for
// correctness rather than speed, so that when looking for one to delete
// we know how much to skip
CacheNoDelete = Cache.end();
--CacheNoDelete;
}
void FFMS_AudioSource::DecodeNextBlock(CacheIterator *pos) {
CurrentFrame = &Frames[PacketNumber];
AVPacket Packet;
if (!ReadPacket(&Packet))
throw FFMS_Exception(FFMS_ERROR_PARSER, FFMS_ERROR_UNKNOWN,
"ReadPacket unexpectedly failed to read a packet");
// ReadPacket may have changed the packet number
CurrentFrame = &Frames[PacketNumber];
CurrentSample = CurrentFrame->SampleStart;
bool GotSamples = false;
uint8_t *Data = Packet.data;
while (Packet.size > 0) {
DecodeFrame.reset();
int GotFrame = 0;
int Ret = avcodec_decode_audio4(CodecContext, DecodeFrame, &GotFrame, &Packet);
// Should only ever happen if the user chose to ignore decoding errors
// during indexing, so continue to just ignore decoding errors
if (Ret < 0) break;
if (Ret > 0) {
Packet.size -= Ret;
Packet.data += Ret;
if (GotFrame && DecodeFrame->nb_samples > 0) {
GotSamples = true;
if (pos)
CacheBlock(*pos);
}
}
}
Packet.data = Data;
FreePacket(&Packet);
// Zero sample packets aren't included in the index
if (GotSamples)
++PacketNumber;
}
