#!/usr/bin/env python

# reference: c041828_ISO_IEC_14496-12_2005(E).pdf

##################################################
# reader and writer
##################################################

import struct
from io import BytesIO

def skip(stream, n):
    stream.seek(stream.tell() + n)

def skip_zeros(stream, n):
    assert stream.read(n) == b'\x00' * n

def read_int(stream):
    return struct.unpack('>i', stream.read(4))[0]

def read_uint(stream):
    return struct.unpack('>I', stream.read(4))[0]

def write_uint(stream, n):
    stream.write(struct.pack('>I', n))

def read_ushort(stream):
    return struct.unpack('>H', stream.read(2))[0]

def read_ulong(stream):
    return struct.unpack('>Q', stream.read(8))[0]

def read_byte(stream):
    return ord(stream.read(1))

def copy_stream(source, target, n):
    buffer_size = 1024 * 1024
    while n > 0:
        to_read = min(buffer_size, n)
        s = source.read(to_read)
        assert len(s) == to_read, 'no enough data'
        target.write(s)
        n -= to_read

class Atom:
    def __init__(self, type, size, body):
        assert len(type) == 4
        self.type = type
        self.size = size
        self.body = body
    def __str__(self):
        #return '<Atom(%s):%s>' % (self.type, repr(self.body))
        return '<Atom(%s):%s>' % (self.type, '')
    def __repr__(self):
        return str(self)
    def write1(self, stream):
        write_uint(stream, self.size)
        stream.write(self.type)
    def write(self, stream):
        assert type(self.body) == bytes, '%s: %s' % (self.type, type(self.body))
        assert self.size == 8 + len(self.body)
        self.write1(stream)
        stream.write(self.body)
    def calsize(self):
        return self.size

class CompositeAtom(Atom):
    def __init__(self, type, size, body):
        assert isinstance(body, list)
        Atom.__init__(self, type, size, body)
    def write(self, stream):
        assert type(self.body) == list
        self.write1(stream)
        for atom in self.body:
            atom.write(stream)
    def calsize(self):
        self.size = 8 + sum([atom.calsize() for atom in self.body])
        return self.size
    def get1(self, k):
        for a in self.body:
            if a.type == k:
                return a
        else:
            raise Exception('atom not found: ' + k)
    def get(self, *keys):
        atom = self
        for k in keys:
            atom = atom.get1(k)
        return atom
    def get_all(self, k):
        return list(filter(lambda x: x.type == k, self.body))

class VariableAtom(Atom):
    def __init__(self, type, size, body, variables):
        assert isinstance(body, bytes)
        Atom.__init__(self, type, size, body)
        self.variables = variables
    def write(self, stream):
        self.write1(stream)
        i = 0
        n = 0
        for name, offset, value in self.variables:
            stream.write(self.body[i:offset])
            write_uint(stream, value)
            n += offset - i + 4
            i = offset + 4
        stream.write(self.body[i:])
        n += len(self.body) - i
        assert n == len(self.body)
    def get(self, k):
        for v in self.variables:
            if v[0] == k:
                return v[2]
        else:
            raise Exception('field not found: ' + k)
    def set(self, k, v):
        for i in range(len(self.variables)):
            variable = self.variables[i]
            if variable[0] == k:
                self.variables[i] = (k, variable[1], v)
                break
        else:
            raise Exception('field not found: '+k)

def read_raw(stream, size, left, type):
    assert size == left + 8
    body = stream.read(left)
    return Atom(type, size, body)

def read_body_stream(stream, left):
    body = stream.read(left)
    assert len(body) == left
    return body, BytesIO(body)

def read_full_atom(stream):
    value = read_uint(stream)
    version = value >> 24
    flags = value & 0xffffff
    assert version == 0
    return value

def read_mvhd(stream, size, left, type):
    body, stream = read_body_stream(stream, left)
    value = read_full_atom(stream)
    left -= 4
    
    # new Date(movieTime * 1000 - 2082850791998L); 
    creation_time = read_uint(stream)
    modification_time = read_uint(stream)
    time_scale = read_uint(stream)
    duration = read_uint(stream)
    left -= 16
    
    qt_preferred_fate = read_uint(stream)
    qt_preferred_volume = read_ushort(stream)
    assert stream.read(10) == b'\x00' * 10
    qt_matrixA = read_uint(stream)
    qt_matrixB = read_uint(stream)
    qt_matrixU = read_uint(stream)
    qt_matrixC = read_uint(stream)
    qt_matrixD = read_uint(stream)
    qt_matrixV = read_uint(stream)
    qt_matrixX = read_uint(stream)
    qt_matrixY = read_uint(stream)
    qt_matrixW = read_uint(stream)
    qt_previewTime = read_uint(stream)
    qt_previewDuration = read_uint(stream)
    qt_posterTime = read_uint(stream)
    qt_selectionTime = read_uint(stream)
    qt_selectionDuration = read_uint(stream)
    qt_currentTime = read_uint(stream)
    nextTrackID = read_uint(stream)
    left -= 80
    assert left == 0
    return VariableAtom(b'mvhd', size, body, [('duration', 16, duration)])

def read_tkhd(stream, size, left, type):
    body, stream = read_body_stream(stream, left)
    value = read_full_atom(stream)
    left -= 4
    
    # new Date(movieTime * 1000 - 2082850791998L); 
    creation_time = read_uint(stream)
    modification_time = read_uint(stream)
    track_id = read_uint(stream)
    assert stream.read(4) == b'\x00' * 4
    duration = read_uint(stream)
    left -= 20
    
    assert stream.read(8) == b'\x00' * 8
    qt_layer = read_ushort(stream)
    qt_alternate_group = read_ushort(stream)
    qt_volume = read_ushort(stream)
    assert stream.read(2) == b'\x00\x00'
    qt_matrixA = read_uint(stream)
    qt_matrixB = read_uint(stream)
    qt_matrixU = read_uint(stream)
    qt_matrixC = read_uint(stream)
    qt_matrixD = read_uint(stream)
    qt_matrixV = read_uint(stream)
    qt_matrixX = read_uint(stream)
    qt_matrixY = read_uint(stream)
    qt_matrixW = read_uint(stream)
    qt_track_width = read_uint(stream)
    width = qt_track_width >> 16
    qt_track_height = read_uint(stream)
    height = qt_track_height >> 16
    left -= 60
    assert left == 0
    return VariableAtom(b'tkhd', size, body, [('duration', 20, duration)])

def read_mdhd(stream, size, left, type):
    body, stream = read_body_stream(stream, left)
    value = read_full_atom(stream)
    left -= 4
    
    # new Date(movieTime * 1000 - 2082850791998L); 
    creation_time = read_uint(stream)
    modification_time = read_uint(stream)
    time_scale = read_uint(stream)
    duration = read_uint(stream)
    left -= 16
    
    packed_language = read_ushort(stream)
    qt_quality = read_ushort(stream)
    left -= 4
    
    assert left == 0
    return VariableAtom(b'mdhd', size, body, [('duration', 16, duration)])

def read_hdlr(stream, size, left, type):
    body, stream = read_body_stream(stream, left)
    value = read_full_atom(stream)
    left -= 4
    
    qt_component_type = read_uint(stream)
    handler_type = read_uint(stream)
    qt_component_manufacturer = read_uint(stream)
    qt_component_flags = read_uint(stream)
    qt_component_flags_mask = read_uint(stream)
    left -= 20
    
    track_name = stream.read(left - 1)
    assert stream.read(1) == b'\x00'
    
    return Atom(b'hdlr', size, body)

def read_vmhd(stream, size, left, type):
    body, stream = read_body_stream(stream, left)
    value = read_full_atom(stream)
    left -= 4
    
    assert left == 8
    graphic_mode = read_ushort(stream)
    op_color_read = read_ushort(stream)
    op_color_green = read_ushort(stream)
    op_color_blue = read_ushort(stream)
    
    return Atom(b'vmhd', size, body)

def read_stsd(stream, size, left, type):
    value = read_full_atom(stream)
    left -= 4
    
    entry_count = read_uint(stream)
    left -= 4
    
    children = []
    for i in range(entry_count):
        atom = read_atom(stream)
        children.append(atom)
        left -= atom.size
    
    assert left == 0
    #return Atom('stsd', size, children)
    class stsd_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            write_uint(stream, self.body[0])
            write_uint(stream, len(self.body[1]))
            for atom in self.body[1]:
                atom.write(stream)
        def calsize(self):
            oldsize = self.size # TODO: remove
            self.size = 8 + 4 + 4 + sum([atom.calsize() for atom in self.body[1]])
            assert oldsize == self.size, '%s: %d, %d' % (self.type, oldsize, self.size) # TODO: remove
            return self.size
    return stsd_atom(b'stsd', size, (value, children))

def read_avc1(stream, size, left, type):
    body, stream = read_body_stream(stream, left)
    
    skip_zeros(stream, 6)
    data_reference_index = read_ushort(stream)
    skip_zeros(stream, 2)
    skip_zeros(stream, 2)
    skip_zeros(stream, 12)
    width = read_ushort(stream)
    height = read_ushort(stream)
    horizontal_rez = read_uint(stream) >> 16
    vertical_rez = read_uint(stream) >> 16
    assert stream.read(4) == b'\x00' * 4
    frame_count = read_ushort(stream)
    string_len = read_byte(stream)
    compressor_name = stream.read(31)
    depth = read_ushort(stream)
    assert stream.read(2) == b'\xff\xff'
    left -= 78
    
    child = read_atom(stream)
    assert child.type in (b'avcC', b'pasp'), 'if the sub atom is not avcC or pasp (actual %s), you should not cache raw body' % child.type
    left -= child.size
    stream.read(left) # XXX
    return Atom(b'avc1', size, body)

def read_avcC(stream, size, left, type):
    stream.read(left)
    return Atom(b'avcC', size, None)

def read_stts(stream, size, left, type):
    value = read_full_atom(stream)
    left -= 4
    
    entry_count = read_uint(stream)
    assert entry_count == 1
    left -= 4
    
    samples = []
    for i in range(entry_count):
            sample_count = read_uint(stream)
            sample_duration = read_uint(stream)
            samples.append((sample_count, sample_duration))
            left -= 8
    
    assert left == 0
    #return Atom('stts', size, None)
    class stts_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            write_uint(stream, self.body[0])
            write_uint(stream, len(self.body[1]))
            for sample_count, sample_duration in self.body[1]:
                write_uint(stream, sample_count)
                write_uint(stream, sample_duration)
        def calsize(self):
            oldsize = self.size # TODO: remove
            self.size = 8 + 4 + 4 + len(self.body[1]) * 8
            assert oldsize == self.size, '%s: %d, %d' % (self.type, oldsize, self.size) # TODO: remove
            return self.size
    return stts_atom(b'stts', size, (value, samples))

def read_stss(stream, size, left, type):
    value = read_full_atom(stream)
    left -= 4
    
    entry_count = read_uint(stream)
    left -= 4
    
    samples = []
    for i in range(entry_count):
            sample = read_uint(stream)
            samples.append(sample)
            left -= 4
    
    assert left == 0
    #return Atom('stss', size, None)
    class stss_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            write_uint(stream, self.body[0])
            write_uint(stream, len(self.body[1]))
            for sample in self.body[1]:
                write_uint(stream, sample)
        def calsize(self):
            self.size = 8 + 4 + 4 + len(self.body[1]) * 4
            return self.size
    return stss_atom(b'stss', size, (value, samples))

def read_stsc(stream, size, left, type):
    value = read_full_atom(stream)
    left -= 4
    
    entry_count = read_uint(stream)
    left -= 4
    
    chunks = []
    for i in range(entry_count):
        first_chunk = read_uint(stream)
        samples_per_chunk = read_uint(stream)
        sample_description_index = read_uint(stream)
        assert sample_description_index == 1 # what is it?
        chunks.append((first_chunk, samples_per_chunk, sample_description_index))
        left -= 12
    #chunks, samples = zip(*chunks)
    #total = 0
    #for c, s in zip(chunks[1:], samples):
    #	total += c*s
    #print 'total', total
    
    assert left == 0
    #return Atom('stsc', size, None)
    class stsc_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            write_uint(stream, self.body[0])
            write_uint(stream, len(self.body[1]))
            for first_chunk, samples_per_chunk, sample_description_index in self.body[1]:
                write_uint(stream, first_chunk)
                write_uint(stream, samples_per_chunk)
                write_uint(stream, sample_description_index)
        def calsize(self):
            self.size = 8 + 4 + 4 + len(self.body[1]) * 12
            return self.size
    return stsc_atom(b'stsc', size, (value, chunks))

def read_stsz(stream, size, left, type):
    value = read_full_atom(stream)
    left -= 4
    
    sample_size = read_uint(stream)
    sample_count = read_uint(stream)
    left -= 8
    
    assert sample_size == 0
    total = 0
    sizes = []
    if sample_size == 0:
        for i in range(sample_count):
            entry_size = read_uint(stream)
            sizes.append(entry_size)
            total += entry_size
            left -= 4
    
    assert left == 0
    #return Atom('stsz', size, None)
    class stsz_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            write_uint(stream, self.body[0])
            write_uint(stream, self.body[1])
            write_uint(stream, self.body[2])
            for entry_size in self.body[3]:
                write_uint(stream, entry_size)
        def calsize(self):
            self.size = 8 + 4 + 8 + len(self.body[3]) * 4
            return self.size
    return stsz_atom(b'stsz', size, (value, sample_size, sample_count, sizes))

def read_stco(stream, size, left, type):
    value = read_full_atom(stream)
    left -= 4
    
    entry_count = read_uint(stream)
    left -= 4
    
    offsets = []
    for i in range(entry_count):
        chunk_offset = read_uint(stream)
        offsets.append(chunk_offset)
        left -= 4
    
    assert left == 0
    #return Atom('stco', size, None)
    class stco_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            write_uint(stream, self.body[0])
            write_uint(stream, len(self.body[1]))
            for chunk_offset in self.body[1]:
                write_uint(stream, chunk_offset)
        def calsize(self):
            self.size = 8 + 4 + 4 + len(self.body[1]) * 4
            return self.size
    return stco_atom(b'stco', size, (value, offsets))

def read_ctts(stream, size, left, type):
    value = read_full_atom(stream)
    left -= 4
    
    entry_count = read_uint(stream)
    left -= 4
    
    samples = []
    for i in range(entry_count):
        sample_count = read_uint(stream)
        sample_offset = read_uint(stream)
        samples.append((sample_count, sample_offset))
        left -= 8
    
    assert left == 0
    class ctts_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            write_uint(stream, self.body[0])
            write_uint(stream, len(self.body[1]))
            for sample_count, sample_offset in self.body[1]:
                write_uint(stream, sample_count)
                write_uint(stream, sample_offset)
        def calsize(self):
            self.size = 8 + 4 + 4 + len(self.body[1]) * 8
            return self.size
    return ctts_atom(b'ctts', size, (value, samples))

def read_smhd(stream, size, left, type):
    body, stream = read_body_stream(stream, left)
    value = read_full_atom(stream)
    left -= 4
    
    balance = read_ushort(stream)
    assert stream.read(2) == b'\x00\x00'
    left -= 4
    
    assert left == 0
    return Atom(b'smhd', size, body)

def read_mp4a(stream, size, left, type):
    body, stream = read_body_stream(stream, left)
    
    assert stream.read(6) == b'\x00' * 6
    data_reference_index = read_ushort(stream)
    assert stream.read(8) == b'\x00' * 8
    channel_count = read_ushort(stream)
    sample_size = read_ushort(stream)
    assert stream.read(4) == b'\x00' * 4
    time_scale = read_ushort(stream)
    assert stream.read(2) == b'\x00' * 2
    left -= 28
    
    atom = read_atom(stream)
    assert atom.type == b'esds'
    left -= atom.size
    
    assert left == 0
    return Atom(b'mp4a', size, body)

def read_descriptor(stream):
    tag = read_byte(stream)
    raise NotImplementedError()

def read_esds(stream, size, left, type):
    value = read_uint(stream)
    version = value >> 24
    assert version == 0
    flags = value & 0xffffff
    left -= 4
    
    body = stream.read(left)
    return Atom(b'esds', size, None)

def read_composite_atom(stream, size, left, type):
    children = []
    while left > 0:
        atom = read_atom(stream)
        children.append(atom)
        left -= atom.size
    assert left == 0, left
    return CompositeAtom(type, size, children)

def read_mdat(stream, size, left, type):
    source_start = stream.tell()
    source_size = left
    skip(stream, left)
    #return Atom(type, size, None)
    #raise NotImplementedError()
    class mdat_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            self.write2(stream)
        def write2(self, stream):
            source, source_start, source_size = self.body
            original = source.tell()
            source.seek(source_start)
            copy_stream(source, stream, source_size)
        def calsize(self):
            return self.size
    return mdat_atom(b'mdat', size, (stream, source_start, source_size))

atom_readers = {
    b'mvhd': read_mvhd, # merge duration
    b'tkhd': read_tkhd, # merge duration
    b'mdhd': read_mdhd, # merge duration
    b'hdlr': read_hdlr, # nothing
    b'vmhd': read_vmhd, # nothing
    b'stsd': read_stsd, # nothing
    b'avc1': read_avc1, # nothing
    b'avcC': read_avcC, # nothing
    b'stts': read_stts, # sample_count, sample_duration
    b'stss': read_stss, # join indexes
    b'stsc': read_stsc, # merge # sample numbers
    b'stsz': read_stsz, # merge # samples
    b'stco': read_stco, # merge # chunk offsets
    b'ctts': read_ctts, # merge
    b'smhd': read_smhd, # nothing
    b'mp4a': read_mp4a, # nothing
    b'esds': read_esds, # noting
    
    b'ftyp': read_raw,
    b'yqoo': read_raw,
    b'moov': read_composite_atom,
    b'trak': read_composite_atom,
    b'mdia': read_composite_atom,
    b'minf': read_composite_atom,
    b'dinf': read_composite_atom,
    b'stbl': read_composite_atom,
    b'iods': read_raw,
    b'dref': read_raw,
    b'free': read_raw,
    b'edts': read_raw,
    b'pasp': read_raw,
    
    b'mdat': read_mdat,
}
#stsd sample descriptions (codec types, initialization etc.) 
#stts (decoding) time-to-sample  
#ctts (composition) time to sample 
#stsc sample-to-chunk, partial data-offset information 
#stsz sample sizes (framing) 
#stz2 compact sample sizes (framing) 
#stco chunk offset, partial data-offset information 
#co64 64-bit chunk offset 
#stss sync sample table (random access points) 
#stsh shadow sync sample table 
#padb sample padding bits 
#stdp sample degradation priority 
#sdtp independent and disposable samples 
#sbgp sample-to-group 
#sgpd sample group description 
#subs sub-sample information


def read_atom(stream):
    header = stream.read(8)
    if not header:
        return
    assert len(header) == 8
    n = 0
    size = struct.unpack('>I', header[:4])[0]
    assert size > 0
    n += 4
    type = header[4:8]
    n += 4
    assert type != b'uuid'
    if size == 1:
        size = read_ulong(stream)
        n += 8
    
    left = size - n
    if type in atom_readers:
        return atom_readers[type](stream, size, left, type)
    raise NotImplementedError('%s: %d' % (type, left))

def write_atom(stream, atom):
    atom.write(stream)

def parse_atoms(stream):
    atoms = []
    while True:
        atom = read_atom(stream)
        if atom:
            atoms.append(atom)
        else:
            break
    return atoms

def read_mp4(stream):
    atoms = parse_atoms(stream)
    moov = list(filter(lambda x: x.type == b'moov', atoms))
    mdat = list(filter(lambda x: x.type == b'mdat', atoms))
    assert len(moov) == 1
    assert len(mdat) == 1
    moov = moov[0]
    mdat = mdat[0]
    return atoms, moov, mdat

##################################################
# merge
##################################################

def merge_stts(samples_list):
    sample_list = []
    for samples in samples_list:
        assert len(samples) == 1
        sample_list.append(samples[0])
    counts, durations = zip(*sample_list)
    assert len(set(durations)) == 1, 'not all durations equal'
    return [(sum(counts), durations[0])]

def merge_stss(samples, sample_number_list):
    results = []
    start = 0
    for samples, sample_number_list in zip(samples, sample_number_list):
        results.extend(map(lambda x: start + x, samples))
        start += sample_number_list
    return results

def merge_stsc(chunks_list, total_chunk_number_list):
    results = []
    chunk_index = 1
    for chunks, total in zip(chunks_list, total_chunk_number_list):
        for i in range(len(chunks)):
            if i < len(chunks) - 1:
                chunk_number = chunks[i + 1][0] - chunks[i][0]
            else:
                chunk_number = total + 1 - chunks[i][0]
            sample_number = chunks[i][1]
            description = chunks[i][2]
            results.append((chunk_index, sample_number, description))
            chunk_index += chunk_number
    return results

def merge_stco(offsets_list, mdats):
    offset = 0
    results = []
    for offsets, mdat in zip(offsets_list, mdats):
        results.extend(offset + x - mdat.body[1] for x in offsets)
        offset += mdat.size - 8
    return results

def merge_stsz(sizes_list):
    return sum(sizes_list, [])

def merge_mdats(mdats):
    total_size = sum(x.size - 8 for x in mdats) + 8
    class multi_mdat_atom(Atom):
        def __init__(self, type, size, body):
            Atom.__init__(self, type, size, body)
        def write(self, stream):
            self.write1(stream)
            self.write2(stream)
        def write2(self, stream):
            for mdat in self.body:
                mdat.write2(stream)
        def calsize(self):
            return self.size
    return multi_mdat_atom(b'mdat', total_size, mdats)

def merge_moov(moovs, mdats):
    mvhd_duration = 0
    for x in moovs:
        mvhd_duration += x.get(b'mvhd').get('duration')
    tkhd_durations = [0, 0]
    mdhd_durations = [0, 0]
    for x in moovs:
        traks = x.get_all(b'trak')
        assert len(traks) == 2
        tkhd_durations[0] += traks[0].get(b'tkhd').get('duration')
        tkhd_durations[1] += traks[1].get(b'tkhd').get('duration')
        mdhd_durations[0] += traks[0].get(b'mdia', b'mdhd').get('duration')
        mdhd_durations[1] += traks[1].get(b'mdia', b'mdhd').get('duration')
    #mvhd_duration = min(mvhd_duration, tkhd_durations)
    
    trak0s = [x.get_all(b'trak')[0] for x in moovs]
    trak1s = [x.get_all(b'trak')[1] for x in moovs]
    
    stts0 = merge_stts(x.get(b'mdia', b'minf', b'stbl', b'stts').body[1] for x in trak0s)
    stts1 = merge_stts(x.get(b'mdia', b'minf', b'stbl', b'stts').body[1] for x in trak1s)
    
    stss = merge_stss((x.get(b'mdia', b'minf', b'stbl', b'stss').body[1] for x in trak0s), (len(x.get(b'mdia', b'minf', b'stbl', b'stsz').body[3]) for x in trak0s))
    
    stsc0 = merge_stsc((x.get(b'mdia', b'minf', b'stbl', b'stsc').body[1] for x in trak0s), (len(x.get(b'mdia', b'minf', b'stbl', b'stco').body[1]) for x in trak0s))
    stsc1 = merge_stsc((x.get(b'mdia', b'minf', b'stbl', b'stsc').body[1] for x in trak1s), (len(x.get(b'mdia', b'minf', b'stbl', b'stco').body[1]) for x in trak1s))
    
    stco0 = merge_stco((x.get(b'mdia', b'minf', b'stbl', b'stco').body[1] for x in trak0s), mdats)
    stco1 = merge_stco((x.get(b'mdia', b'minf', b'stbl', b'stco').body[1] for x in trak1s), mdats)
    
    stsz0 = merge_stsz((x.get(b'mdia', b'minf', b'stbl', b'stsz').body[3] for x in trak0s))
    stsz1 = merge_stsz((x.get(b'mdia', b'minf', b'stbl', b'stsz').body[3] for x in trak1s))
    
    ctts = sum((x.get(b'mdia', b'minf', b'stbl', b'ctts').body[1] for x in trak0s), [])
    
    moov = moovs[0]
    
    moov.get(b'mvhd').set('duration', mvhd_duration)
    trak0 = moov.get_all(b'trak')[0]
    trak1 = moov.get_all(b'trak')[1]
    trak0.get(b'tkhd').set('duration', tkhd_durations[0])
    trak1.get(b'tkhd').set('duration', tkhd_durations[1])
    trak0.get(b'mdia', b'mdhd').set('duration', mdhd_durations[0])
    trak1.get(b'mdia', b'mdhd').set('duration', mdhd_durations[1])
    
    stts_atom = trak0.get(b'mdia', b'minf', b'stbl', b'stts')
    stts_atom.body = stts_atom.body[0], stts0
    stts_atom = trak1.get(b'mdia', b'minf', b'stbl', b'stts')
    stts_atom.body = stts_atom.body[0], stts1
    
    stss_atom = trak0.get(b'mdia', b'minf', b'stbl', b'stss')
    stss_atom.body = stss_atom.body[0], stss
    
    stsc_atom = trak0.get(b'mdia', b'minf', b'stbl', b'stsc')
    stsc_atom.body = stsc_atom.body[0], stsc0
    stsc_atom = trak1.get(b'mdia', b'minf', b'stbl', b'stsc')
    stsc_atom.body = stsc_atom.body[0], stsc1
    
    stco_atom = trak0.get(b'mdia', b'minf', b'stbl', b'stco')
    stco_atom.body = stss_atom.body[0], stco0
    stco_atom = trak1.get(b'mdia', b'minf', b'stbl', b'stco')
    stco_atom.body = stss_atom.body[0], stco1
    
    stsz_atom = trak0.get(b'mdia', b'minf', b'stbl', b'stsz')
    stsz_atom.body = stsz_atom.body[0], stsz_atom.body[1], len(stsz0), stsz0
    stsz_atom = trak1.get(b'mdia', b'minf', b'stbl', b'stsz')
    stsz_atom.body = stsz_atom.body[0], stsz_atom.body[1], len(stsz1), stsz1
    
    ctts_atom = trak0.get(b'mdia', b'minf', b'stbl', b'ctts')
    ctts_atom.body = ctts_atom.body[0], ctts
    
    old_moov_size = moov.size
    new_moov_size = moov.calsize()
    new_mdat_start = mdats[0].body[1] + new_moov_size - old_moov_size
    stco0 = list(map(lambda x: x + new_mdat_start, stco0))
    stco1 = list(map(lambda x: x + new_mdat_start, stco1))
    stco_atom = trak0.get(b'mdia', b'minf', b'stbl', b'stco')
    stco_atom.body = stss_atom.body[0], stco0
    stco_atom = trak1.get(b'mdia', b'minf', b'stbl', b'stco')
    stco_atom.body = stss_atom.body[0], stco1
    
    return moov

def merge_mp4s(files, output):
    assert files
    ins = [open(mp4, 'rb') for mp4 in files]
    mp4s = list(map(read_mp4, ins))
    moovs = list(map(lambda x: x[1], mp4s))
    mdats = list(map(lambda x: x[2], mp4s))
    moov = merge_moov(moovs, mdats)
    mdat = merge_mdats(mdats)
    with open(output, 'wb') as output:
        for x in mp4s[0][0]:
            if x.type == b'moov':
                moov.write(output)
            elif x.type == b'mdat':
                mdat.write(output)
            else:
                x.write(output)

##################################################
# main
##################################################

# TODO: FIXME: duplicate of join_flv

def guess_output(inputs):
    import os.path
    inputs = map(os.path.basename, inputs)
    n = min(map(len, inputs))
    for i in reversed(range(1, n)):
        if len(set(s[:i] for s in inputs)) == 1:
            return inputs[0][:i] + '.mp4'
    return 'output.mp4'

def concat_mp4(mp4s, output = None):
    assert mp4s, 'no mp4 file found'
    import os.path
    if not output:
        output = guess_output(mp4s)
    elif os.path.isdir(output):
        output = os.path.join(output, guess_output(mp4s))
    
    print('Merging video parts...')
    merge_mp4s(mp4s, output)
    
    return output

def usage():
    print('Usage: [python3] join_mp4.py --output TARGET.mp4 mp4...')

def main():
    import sys, getopt
    try:
        opts, args = getopt.getopt(sys.argv[1:], "ho:", ["help", "output="])
    except getopt.GetoptError as err:
        usage()
        sys.exit(1)
    output = None
    for o, a in opts:
        if o in ("-h", "--help"):
            usage()
            sys.exit()
        elif o in ("-o", "--output"):
            output = a
        else:
            usage()
            sys.exit(1)
    if not args:
        usage()
        sys.exit(1)
    
    concat_mp4(args, output)

if __name__ == '__main__':
    main()