def read(cls, a):
# from mp4split
esdesc = atoms.read_uchar(a.f)
if esdesc == MP4_ELEMENTARY_STREAM_DESCRIPTOR_TAG:
len = read_desc_len(a.f)
stream_id = atoms.read_ushort(a.f)
prio = atoms.read_uchar(a.f)
else:
stream_id = atoms.read_ushort(a.f)
tag = atoms.read_uchar(a.f)
len = read_desc_len(a.f)
if tag != MP4_DECODER_CONFIG_DESCRIPTOR_TAG:
raise FormatError("can't parse esds")
object_type_id = atoms.read_uchar(a.f)
stream_type = atoms.read_uchar(a.f)
buffer_size_db = a.read_bytes(3)
maxBitrate = atoms.read_ulong(a.f)
avgBitrate = atoms.read_ulong(a.f)
tag = atoms.read_uchar(a.f)
len = read_desc_len(a.f)
if tag != MP4_DECODER_SPECIFIC_DESCRIPTOR_TAG:
raise FormatError("can't parse esd")
data = a.read_bytes(len)
return cls(a, object_type_id=object_type_id,
maxBitrate=maxBitrate, avgBitrate=avgBitrate, data=data)
def read_desc_len(f):
bytes = 0
len = 0
while True:
c = atoms.read_uchar(f)
len <<= 7
len |= c & 0x7f
bytes += 1
if (bytes == 4):
break
if not (c & 0x80):
break
return len
