internal DecoderConfiguration(ref Reader reader)
{
var dcd = reader.readStructure <DecoderConfigDescriptor>();
objectType = (eObjectType)dcd.objectTypeIndication;
streamType = (eStreamType)dcd.streamType;
upStream = dcd.upStream;
decodingBufferSize = dcd.bufferSizeDB;
maximumBitrate = dcd.maxBitrate;
averageBitrate = dcd.avgBitrate;
// The reader gotta be positioned at the start of AudioSpecificConfig tag.
// See ISO/IEC 14496-1 annex "E" for more info on tags and sizes.
eDescriptorTag tag = (eDescriptorTag)reader.readByte();
if (tag != eDescriptorTag.DecoderSpecificInfo)
{
throw new ArgumentException($"Expected eDescriptorTag.DecoderSpecificInfo, got { tag } instead");
}
int cb = reader.readSize();
if (reader.bytesLeft < cb)
{
throw new EndOfStreamException($"DecoderSpecificInfo has size { cb } in the header, yet the stream only has { reader.bytesLeft } unread bytes left");
}
audioSpecificConfig = new byte[cb];
reader.readBytes(audioSpecificConfig.AsSpan());
}
public MP4AudioSampleEntry(Mp4Reader mp4, int bytesLeft) :
base(mp4, ref bytesLeft)
{
Span <byte> bytes = stackalloc byte[bytesLeft];
mp4.read(bytes);
int atomSize = BitConverter.ToInt32(bytes).endian();
uint atomTag = BitConverter.ToUInt32(bytes.Slice(4));
switch (atomTag)
{
case (uint)eAudioBoxType.esds:
break;
default:
throw new NotImplementedException();
}
// Skip header, version and flags
bytes = bytes.Slice(12);
Reader streamReader = new Reader(bytes);
if (streamReader.EOF)
{
throw new ArgumentException($"The `esds` atom is empty");
}
// Read tag and size
eDescriptorTag tag = streamReader.readTag();
if (eDescriptorTag.ElementaryStream != tag)
{
throw new ArgumentException($"The `esds` atom is expected to contain an elementary stream descriptor, got { tag } instead");
}
int size = streamReader.readSize();
// Create a reader for the content
Reader esdReader = streamReader.readSubStream(size);
// Read ElementaryStreamDescriptor
ElementaryStreamDescriptor esd = esdReader.readStructure <ElementaryStreamDescriptor>();
id = esd.id;
flags = esd.flags;
priority = esd.priority;
if (esd.flags.HasFlag(eDescriptorFlags.DependentStream))
{
dependsOn = esdReader.readStructure <ushort>().endian();
}
if (esd.flags.HasFlag(eDescriptorFlags.URL))
{
byte urlLength = esdReader.readByte();
Span <byte> urlBuffer = stackalloc byte[urlLength];
esdReader.readBytes(urlBuffer);
unsafe
{
fixed(byte *ptr = urlBuffer)
url = StringMarshal.copy(ptr, urlLength);
}
}
if (esd.flags.HasFlag(eDescriptorFlags.OCRstream))
{
esId = esdReader.readStructure <ushort>().endian();
}
while (!esdReader.EOF)
{
tag = esdReader.readTag();
size = esdReader.readSize();
Reader ss = esdReader.readSubStream(size);
switch (tag)
{
case eDescriptorTag.DecoderConfiguration:
decoderConfig = new DecoderConfiguration(ref ss);
break;
case eDescriptorTag.SyncLayerConfiguration:
syncLayerConfig = new SyncLayerConfiguration(ref ss);
break;
case eDescriptorTag.ProfileLevelIndicationIndex:
profileLevelIndicationindex = ss.readByte();
break;
case eDescriptorTag.IPIdentificationPointer:
case eDescriptorTag.IPMPPointer:
case eDescriptorTag.Language:
case eDescriptorTag.QoS:
case eDescriptorTag.Registration:
// Because of the way we implemented readSubStream, this break will skip them gracefully.
// TODO: support at least language, likely to be seen in the wild
break;
default:
throw new NotSupportedException();
}
}
// TODO: the esdReader has EOF, but the outer one, streamReader, might have not. It might contain moar stuff.
// You can test for `if( !streamReader.EOF )` here, and parse even moar garbage carefully designed by these ISO/IEC committees and documented in many thousands of pages of these PDFs they sell.
}