Example #1
0
/*----------------------------------------------------------------------
|   AP4_Processor::Process
+---------------------------------------------------------------------*/
AP4_Result
AP4_Processor::Process(AP4_ByteStream&   input, 
                       AP4_ByteStream&   output,
                       ProgressListener* listener,
                       AP4_AtomFactory&  atom_factory)
{
    // read all atoms 
    AP4_AtomParent top_level;
    AP4_Atom*      atom;
    while (AP4_SUCCEEDED(atom_factory.CreateAtomFromStream(input, atom))) {
        top_level.AddChild(atom);
    }

    // remove the [mdat] atom, keep a ref to [moov]
    AP4_MoovAtom* moov = NULL;
    AP4_List<AP4_Atom>::Item* atom_item = top_level.GetChildren().FirstItem();
    while (atom_item) {
        atom = atom_item->GetData();
        AP4_List<AP4_Atom>::Item* next = atom_item->GetNext();
        if (atom->GetType() == AP4_ATOM_TYPE_MDAT) {
            atom->Detach();
            delete atom;
        } else if (atom->GetType() == AP4_ATOM_TYPE_MOOV) {
            moov = (AP4_MoovAtom*)atom;
        }
        atom_item = next;
    }

    // initialize the processor
    AP4_Result result = Initialize(top_level, input);
    if (AP4_FAILED(result)) return result;

    // process the tracks if we have a moov atom
    AP4_Array<AP4_SampleLocator> locators;
    AP4_Cardinal                 track_count       = 0;
    AP4_List<AP4_TrakAtom>*      trak_atoms        = NULL;
    AP4_LargeSize                mdat_payload_size = 0;
    TrackHandler**               handlers          = NULL;
    AP4_SampleCursor*            cursors           = NULL;
    if (moov) {
        // build an array of track sample locators
        trak_atoms = &moov->GetTrakAtoms();
        track_count = trak_atoms->ItemCount();
        cursors = new AP4_SampleCursor[track_count];
        handlers = new TrackHandler*[track_count];
        for (AP4_Ordinal i=0; i<track_count; i++) {
            handlers[i] = NULL;
        }
        
        unsigned int index = 0;
        for (AP4_List<AP4_TrakAtom>::Item* item = trak_atoms->FirstItem(); item; item=item->GetNext()) {
            AP4_TrakAtom* trak = item->GetData();

            // find the stsd atom
            AP4_ContainerAtom* stbl = AP4_DYNAMIC_CAST(AP4_ContainerAtom, trak->FindChild("mdia/minf/stbl"));
            if (stbl == NULL) continue;
            
            // see if there's an external data source for this track
            AP4_ByteStream* trak_data_stream = &input;
            for (AP4_List<ExternalTrackData>::Item* ditem = m_ExternalTrackData.FirstItem(); ditem; ditem=ditem->GetNext()) {
                ExternalTrackData* tdata = ditem->GetData();
                if (tdata->m_TrackId == trak->GetId()) {
                    trak_data_stream = tdata->m_MediaData;
                    break;
                }
            }

            // create the track handler    
            handlers[index] = CreateTrackHandler(trak);
            cursors[index].m_Locator.m_TrakIndex   = index;
            cursors[index].m_Locator.m_SampleTable = new AP4_AtomSampleTable(stbl, *trak_data_stream);
            cursors[index].m_Locator.m_SampleIndex = 0;
            cursors[index].m_Locator.m_ChunkIndex  = 0;
            cursors[index].m_Locator.m_SampleTable->GetSample(0, cursors[index].m_Locator.m_Sample);

            index++;            
        }

        // figure out the layout of the chunks
        for (;;) {
            // see which is the next sample to write
            AP4_UI64 min_offset = (AP4_UI64)(-1);
            int cursor = -1;
            for (unsigned int i=0; i<track_count; i++) {
                if (!cursors[i].m_EndReached &&
                    cursors[i].m_Locator.m_Sample.GetOffset() <= min_offset) {
                    min_offset = cursors[i].m_Locator.m_Sample.GetOffset();
                    cursor = i;
                }
            }

            // stop if all cursors are exhausted
            if (cursor == -1) break;

            // append this locator to the layout list
            AP4_SampleLocator& locator = cursors[cursor].m_Locator;
            locators.Append(locator);

            // move the cursor to the next sample
            locator.m_SampleIndex++;
            if (locator.m_SampleIndex == locator.m_SampleTable->GetSampleCount()) {
                // mark this track as completed
                cursors[cursor].m_EndReached = true;
            } else {
                // get the next sample info
                locator.m_SampleTable->GetSample(locator.m_SampleIndex, locator.m_Sample);
                AP4_Ordinal skip, sdesc;
                locator.m_SampleTable->GetChunkForSample(locator.m_SampleIndex,
                                                         locator.m_ChunkIndex,
                                                         skip, sdesc);
            }
        }

        // update the stbl atoms and compute the mdat size
        int current_track = -1;
        int current_chunk = -1;
        AP4_Position current_chunk_offset = 0;
        AP4_Size current_chunk_size = 0;
        for (AP4_Ordinal i=0; i<locators.ItemCount(); i++) {
            AP4_SampleLocator& locator = locators[i];
            if ((int)locator.m_TrakIndex  != current_track ||
                (int)locator.m_ChunkIndex != current_chunk) {
                // start a new chunk for this track
                current_chunk_offset += current_chunk_size;
                current_chunk_size = 0;
                current_track = locator.m_TrakIndex;
                current_chunk = locator.m_ChunkIndex;
                locator.m_SampleTable->SetChunkOffset(locator.m_ChunkIndex, current_chunk_offset);
            } 
            AP4_Size sample_size;
            TrackHandler* handler = handlers[locator.m_TrakIndex];
            if (handler) {
                sample_size = handler->GetProcessedSampleSize(locator.m_Sample);
                locator.m_SampleTable->SetSampleSize(locator.m_SampleIndex, sample_size);
            } else {
                sample_size = locator.m_Sample.GetSize();
            }
            current_chunk_size += sample_size;
            mdat_payload_size  += sample_size;
        }

        // process the tracks (ex: sample descriptions processing)
        for (AP4_Ordinal i=0; i<track_count; i++) {
            TrackHandler* handler = handlers[i];
            if (handler) handler->ProcessTrack();
        }
    }

    // initialize the processor
    Finalize(top_level);

    // calculate the size of all atoms combined
    AP4_UI64 atoms_size = 0;
    top_level.GetChildren().Apply(AP4_AtomSizeAdder(atoms_size));

    // see if we need a 64-bit or 32-bit mdat
    AP4_Size mdat_header_size = AP4_ATOM_HEADER_SIZE;
    if (mdat_payload_size+mdat_header_size > 0xFFFFFFFF) {
        // we need a 64-bit size
        mdat_header_size += 8;
    }
    
    // adjust the chunk offsets
    for (AP4_Ordinal i=0; i<track_count; i++) {
        AP4_TrakAtom* trak;
        trak_atoms->Get(i, trak);
        trak->AdjustChunkOffsets(atoms_size+mdat_header_size);
    }

    // write all atoms
    top_level.GetChildren().Apply(AP4_AtomListWriter(output));

    // write mdat header
    if (mdat_payload_size) {
        if (mdat_header_size == AP4_ATOM_HEADER_SIZE) {
            // 32-bit size
            output.WriteUI32((AP4_UI32)(mdat_header_size+mdat_payload_size));
            output.WriteUI32(AP4_ATOM_TYPE_MDAT);
        } else {
            // 64-bit size
            output.WriteUI32(1);
            output.WriteUI32(AP4_ATOM_TYPE_MDAT);
            output.WriteUI64(mdat_header_size+mdat_payload_size);
        }
    }
    
#if defined(AP4_DEBUG)
    AP4_Position before;
    output.Tell(before);
#endif

    // write the samples
    if (moov) {
        AP4_Sample     sample;
        AP4_DataBuffer data_in;
        AP4_DataBuffer data_out;
        for (unsigned int i=0; i<locators.ItemCount(); i++) {
            AP4_SampleLocator& locator = locators[i];
            locator.m_Sample.ReadData(data_in);
            TrackHandler* handler = handlers[locator.m_TrakIndex];
            if (handler) {
                result = handler->ProcessSample(data_in, data_out);
                if (AP4_FAILED(result)) return result;
                output.Write(data_out.GetData(), data_out.GetDataSize());
            } else {
                output.Write(data_in.GetData(), data_in.GetDataSize());            
            }

            // notify the progress listener
            if (listener) {
                listener->OnProgress(i+1, locators.ItemCount());
            }
        }

        // cleanup
        for (AP4_Ordinal i=0; i<track_count; i++) {
            delete cursors[i].m_Locator.m_SampleTable;
            delete handlers[i];
        }
        delete[] cursors;
        delete[] handlers;
    }

#if defined(AP4_DEBUG)
    AP4_Position after;
    output.Tell(after);
    AP4_ASSERT(after-before == mdat_payload_size);
#endif

    return AP4_SUCCESS;
}
/*----------------------------------------------------------------------
|   main
+---------------------------------------------------------------------*/
int
main(int argc, char** argv)
{
    if (argc < 2) {
        PrintUsageAndExit();
    }
    
    // default options
    Options.verbose                = false;
    Options.input                  = NULL;
    Options.init_segment_name      = AP4_SPLIT_DEFAULT_INIT_SEGMENT_NAME;
    Options.media_segment_name     = AP4_SPLIT_DEFAULT_MEDIA_SEGMENT_NAME;
    Options.pattern_params         = AP4_SPLIT_DEFAULT_PATTERN_PARAMS;
    Options.start_number           = 1;
    Options.track_id               = 0;
    Options.audio_only             = false;
    Options.video_only             = false;
    Options.init_only              = false;
    Options.track_filter           = 0;
    
    // parse command line
    AP4_Result result;
    char** args = argv+1;
    while (const char* arg = *args++) {
        if (!strcmp(arg, "--verbose")) {
            Options.verbose = true;
        } else if (!strcmp(arg, "--init-segment")) {
            if (*args == NULL) {
                fprintf(stderr, "ERROR: missing argument after --init-segment option\n");
                return 1;
            }
            Options.init_segment_name = *args++;
        } else if (!strcmp(arg, "--media-segment")) {
            if (*args == NULL) {
                fprintf(stderr, "ERROR: missing argument after --media-segment option\n");
                return 1;
            }
            Options.media_segment_name = *args++;
        } else if (!strcmp(arg, "--pattern-parameters")) {
            if (*args == NULL) {
                fprintf(stderr, "ERROR: missing argument after --pattern-params option\n");
                return 1;
            }
            Options.pattern_params = *args++;
        } else if (!strcmp(arg, "--track-id")) {
            Options.track_id = strtoul(*args++, NULL, 10);
        } else if (!strcmp(arg, "--start-number")) {
            Options.start_number = strtoul(*args++, NULL, 10);
        } else if (!strcmp(arg, "--init-only")) {
            Options.init_only = true;
        } else if (!strcmp(arg, "--audio")) {
            Options.audio_only = true;
        } else if (!strcmp(arg, "--video")) {
            Options.video_only = true;
        } else if (Options.input == NULL) {
            Options.input = arg;
        } else {
            fprintf(stderr, "ERROR: unexpected argument\n");
            return 1;
        }
    }

    // check args
    if (Options.input == NULL) {
        fprintf(stderr, "ERROR: missing input file name\n");
        return 1;
    }
    if ((Options.audio_only && (Options.video_only || Options.track_id)) ||
        (Options.video_only && (Options.audio_only || Options.track_id)) ||
        (Options.track_id   && (Options.audio_only || Options.video_only))) {
        fprintf(stderr, "ERROR: --audio, --video and --track-id options are mutualy exclusive\n");
        return 1;
    }
    if (strlen(Options.pattern_params) < 1) {
        fprintf(stderr, "ERROR: --pattern-params argument is too short\n");
        return 1;
    }
    if (strlen(Options.pattern_params) > 2) {
        fprintf(stderr, "ERROR: --pattern-params argument is too long\n");
        return 1;
    }
    const char* cursor = Options.pattern_params;
    while (*cursor) {
        if (*cursor != 'I' && *cursor != 'N') {
            fprintf(stderr, "ERROR: invalid pattern parameter '%c'\n", *cursor);
            return 1;
        }
        ++cursor;
    }
    
	// create the input stream
    AP4_ByteStream* input = NULL;
    result = AP4_FileByteStream::Create(Options.input, AP4_FileByteStream::STREAM_MODE_READ, input);
    if (AP4_FAILED(result)) {
        fprintf(stderr, "ERROR: cannot open input (%d)\n", result);
        return 1;
    }
    
    // get the movie
    AP4_File* file = new AP4_File(*input, AP4_DefaultAtomFactory::Instance, true);
    AP4_Movie* movie = file->GetMovie();
    if (movie == NULL) {
        fprintf(stderr, "no movie found in file\n");
        return 1;
    }
    
    // filter tracks if required
    if (Options.audio_only) {
        AP4_Track* track = movie->GetTrack(AP4_Track::TYPE_AUDIO);
        if (track == NULL) {
            fprintf(stderr, "--audio option specified, but no audio track found\n");
            return 1;
        }
        Options.track_filter = track->GetId();
    } else if (Options.video_only) {
        AP4_Track* track = movie->GetTrack(AP4_Track::TYPE_VIDEO);
        if (track == NULL) {
            fprintf(stderr, "--video option specified, but no video track found\n");
            return 1;
        }
        Options.track_filter = track->GetId();
    } else if (Options.track_id) {
        AP4_Track* track = movie->GetTrack(Options.track_id);
        if (track == NULL) {
            fprintf(stderr, "--track-id option specified, but no such track found\n");
            return 1;
        }
        Options.track_filter = track->GetId();
    }
    
    // save the init segment
    AP4_ByteStream* output = NULL;
    result = AP4_FileByteStream::Create(Options.init_segment_name, AP4_FileByteStream::STREAM_MODE_WRITE, output);
    if (AP4_FAILED(result)) {
        fprintf(stderr, "ERROR: cannot open output file (%d)\n", result);
        return 1;
    }
    AP4_FtypAtom* ftyp = file->GetFileType(); 
    if (ftyp) {
        result = ftyp->Write(*output);
        if (AP4_FAILED(result)) {
            fprintf(stderr, "ERROR: cannot write ftyp segment (%d)\n", result);
            return 1;
        }
    }
    if (Options.track_filter) {
        AP4_MoovAtom* moov = movie->GetMoovAtom();
        
        // only keep the 'trak' atom that we need
        AP4_List<AP4_Atom>::Item* child = moov->GetChildren().FirstItem();
        while (child) {
            AP4_Atom* atom = child->GetData();
            child = child->GetNext();
            if (atom->GetType() == AP4_ATOM_TYPE_TRAK) {
                AP4_TrakAtom* trak = (AP4_TrakAtom*)atom;
                AP4_TkhdAtom* tkhd = (AP4_TkhdAtom*)trak->GetChild(AP4_ATOM_TYPE_TKHD);
                if (tkhd && tkhd->GetTrackId() != Options.track_filter) {
                    atom->Detach();
                    delete atom;
                }
            }
        }

        // only keep the 'trex' atom that we need
        AP4_ContainerAtom* mvex = AP4_DYNAMIC_CAST(AP4_ContainerAtom, moov->GetChild(AP4_ATOM_TYPE_MVEX));
        if (mvex) {
            child = mvex->GetChildren().FirstItem();
            while (child) {
                AP4_Atom* atom = child->GetData();
                child = child->GetNext();
                if (atom->GetType() == AP4_ATOM_TYPE_TREX) {
                    AP4_TrexAtom* trex = AP4_DYNAMIC_CAST(AP4_TrexAtom, atom);
                    if (trex && trex->GetTrackId() != Options.track_filter) {
                        atom->Detach();
                        delete atom;
                    }
                }
            }
        }
    }
    result = movie->GetMoovAtom()->Write(*output);
    if (AP4_FAILED(result)) {
        fprintf(stderr, "ERROR: cannot write init segment (%d)\n", result);
        return 1;
    }
        
    AP4_Atom* atom = NULL;
    unsigned int track_id = 0;
    for (;!Options.init_only;) {
        // process the next atom
        result = AP4_DefaultAtomFactory::Instance.CreateAtomFromStream(*input, atom);
        if (AP4_FAILED(result)) break;
        
        if (atom->GetType() == AP4_ATOM_TYPE_MOOF) {
            AP4_ContainerAtom* moof = AP4_DYNAMIC_CAST(AP4_ContainerAtom, atom);

            unsigned int traf_count = 0;
            AP4_ContainerAtom* traf = NULL;
            do {
                traf = AP4_DYNAMIC_CAST(AP4_ContainerAtom, moof->GetChild(AP4_ATOM_TYPE_TRAF, traf_count));
                if (traf == NULL) break;
                AP4_TfhdAtom* tfhd = AP4_DYNAMIC_CAST(AP4_TfhdAtom, traf->GetChild(AP4_ATOM_TYPE_TFHD));
                if (tfhd == NULL) {
                    fprintf(stderr, "ERROR: invalid media format\n");
                    return 1;                    
                }
                track_id = tfhd->GetTrackId();
                traf_count++;
            } while (traf);
    
            // check if this fragment has more than one traf
            if (traf_count > 1) {
                if (Options.audio_only) {
                    fprintf(stderr, "ERROR: --audio option incompatible with multi-track fragments");
                    return 1;
                }
                if (Options.video_only) {
                    fprintf(stderr, "ERROR: --video option incompatible with multi-track fragments");
                    return 1;
                }
                track_id = 0;
            }
            
            // open a new file for this fragment
            if (output) {
                output->Release();
                output = NULL;
            }
            char segment_name[4096];
            if (Options.track_filter == 0 || Options.track_filter == track_id) {
                AP4_UI64 p[2] = {0,0};
                unsigned int params_len = strlen(Options.pattern_params);
                for (unsigned int i=0; i<params_len; i++) {
                    if (Options.pattern_params[i] == 'I') {
                        p[i] = track_id;
                    } else if (Options.pattern_params[i] == 'N') {
                        p[i] = NextFragmentIndex(track_id)+Options.start_number;
                    }
                }
                switch (params_len) {
                    case 1:
                        sprintf(segment_name, Options.media_segment_name, p[0]);
                        break;
                    case 2:
                        sprintf(segment_name, Options.media_segment_name, p[0], p[1]);
                        break;
                    default:
                        segment_name[0] = 0;
                        break;
                }
                result = AP4_FileByteStream::Create(segment_name, AP4_FileByteStream::STREAM_MODE_WRITE, output);
                if (AP4_FAILED(result)) {
                    fprintf(stderr, "ERROR: cannot open output file (%d)\n", result);
                    return 1;
                }
            }
        }
        
        // write the atom
        if (output && atom->GetType() != AP4_ATOM_TYPE_MFRA) {
            atom->Write(*output);
        }
        delete atom;
    }

    // cleanup
    delete file;
    if (input) input->Release();
    if (output) output->Release();
    
    return 0;
}
Example #3
0
/*----------------------------------------------------------------------
|       AP4_MoovAtom::AP4_MoovAtom
+---------------------------------------------------------------------*/
AP4_MoovAtom::AP4_MoovAtom(AP4_Size         size,
                           AP4_ByteStream&  stream,
                           AP4_AtomFactory& atom_factory) :
    AP4_ContainerAtom(AP4_ATOM_TYPE_MOOV, size, false, stream, atom_factory),
    m_TimeScale(0)
{
	if(AP4_ContainerAtom* cmov = dynamic_cast<AP4_ContainerAtom*>(GetChild(AP4_ATOM_TYPE_CMOV)))
	{
		AP4_DcomAtom* dcom = dynamic_cast<AP4_DcomAtom*>(cmov->GetChild(AP4_ATOM_TYPE_DCOM));
		AP4_CmvdAtom* cmvd = dynamic_cast<AP4_CmvdAtom*>(cmov->GetChild(AP4_ATOM_TYPE_CMVD));

		if(dcom && dcom->GetCompressorSubType() == AP4_ATOM_TYPE('z','l','i','b') && cmvd)
		{
			const AP4_DataBuffer& data = cmvd->GetDataBuffer();

			z_stream d_stream;
			d_stream.zalloc = (alloc_func)0;
			d_stream.zfree = (free_func)0;
			d_stream.opaque = (voidpf)0;

			int res;

			if(Z_OK == (res = inflateInit(&d_stream)))
			{
				d_stream.next_in = (Bytef*)data.GetData();
				d_stream.avail_in = data.GetDataSize();

				unsigned char* dst = NULL;
				int n = 0;
				
				do
				{
					dst = (unsigned char*)realloc(dst, ++n*1000);
					d_stream.next_out = &dst[(n-1)*1000];
					d_stream.avail_out = 1000;

					if(Z_OK != (res = inflate(&d_stream, Z_NO_FLUSH)) && Z_STREAM_END != res)
					{
						free(dst);
						dst = NULL;
						break;
					}
				}
				while(0 == d_stream.avail_out && 0 != d_stream.avail_in && Z_STREAM_END != res);

				inflateEnd(&d_stream);

				if(dst)
				{
					AP4_ByteStream* s = new AP4_MemoryByteStream(dst, d_stream.total_out);
					ReadChildren(atom_factory, *s, d_stream.total_out);
					s->Release();
					free(dst);
				}

				if(AP4_MoovAtom* moov = dynamic_cast<AP4_MoovAtom*>(GetChild(AP4_ATOM_TYPE_MOOV)))
				{
					AP4_List<AP4_Atom> Children;

					for(AP4_List<AP4_Atom>::Item* item = moov->GetChildren().FirstItem(); 
						item; 
						item = item->GetNext())
					{
						Children.Add(item->GetData());
					}

					for(AP4_List<AP4_Atom>::Item* item = Children.FirstItem(); 
						item; 
						item = item->GetNext())
					{
						AP4_Atom* atom = item->GetData();
						atom->Detach();
						atom->SetParent(this);
						m_Children.Add(atom);
					}

					moov->Detach();
					delete moov;
				}
			}
		}
	}

    // collect all trak atoms
    m_Children.Apply(AP4_TrakAtomCollector(&m_TrakAtoms));    
}
Example #4
0
/*----------------------------------------------------------------------
|       AP4_Processor::Process
+---------------------------------------------------------------------*/
AP4_Result
AP4_Processor::Process(AP4_ByteStream&  input, 
                       AP4_ByteStream&  output,
                       AP4_AtomFactory& atom_factory)
{
    // read all atoms 
    AP4_AtomParent top_level;
    AP4_Atom* atom;
    while (AP4_SUCCEEDED(atom_factory.CreateAtomFromStream(input, atom))) {
        top_level.AddChild(atom);
    }

    // remove the [mdat] and [free] atoms, keep a ref to [moov]
    AP4_MoovAtom* moov = NULL;
    AP4_List<AP4_Atom>::Item* atom_item = top_level.GetChildren().FirstItem();
    while (atom_item) {
        atom = atom_item->GetData();
        AP4_List<AP4_Atom>::Item* next = atom_item->GetNext();
        if (//atom->GetType() == AP4_ATOM_TYPE_FREE ||
            atom->GetType() == AP4_ATOM_TYPE_MDAT) {
            atom->Detach();
            delete atom;
        } else if (atom->GetType() == AP4_ATOM_TYPE_MOOV) {
            moov = (AP4_MoovAtom*)atom;
        }
        atom_item = next;
    }

    // check that we have a moov atom
    if (moov == NULL) return AP4_FAILURE;

    // initialize the processor
    AP4_Result result = Initialize(top_level);
    if (AP4_FAILED(result)) return result;

    // build an array of track sample cursors
    AP4_List<AP4_TrakAtom>& trak_atoms = moov->GetTrakAtoms();
    AP4_Cardinal track_count = trak_atoms.ItemCount();
    AP4_SampleCursor* cursors = new AP4_SampleCursor[track_count];
    TrackHandler** handlers = new TrackHandler*[track_count];
    AP4_List<AP4_TrakAtom>::Item* item = trak_atoms.FirstItem();
    unsigned int index = 0;
    while (item) {
        // create the track handler    // find the stsd atom
        AP4_ContainerAtom* stbl = dynamic_cast<AP4_ContainerAtom*>(
            item->GetData()->FindChild("mdia/minf/stbl"));
        if (stbl == NULL) continue;
        handlers[index] = CreateTrackHandler(item->GetData());
        cursors[index].m_Locator.m_TrakIndex = index;
        cursors[index].m_Locator.m_SampleTable = new AP4_AtomSampleTable(stbl, input);
        cursors[index].m_Locator.m_SampleIndex = 0;
        cursors[index].m_Locator.m_SampleTable->GetSample(0, cursors[index].m_Locator.m_Sample);
        cursors[index].m_Locator.m_Chunk = 1;
        index++;
        item = item->GetNext();
    }

    // figure out the layout of the chunks
    AP4_Array<AP4_SampleLocator> locators;
    for (;;) {
        // see which is the next sample to write
        unsigned int min_offset = 0xFFFFFFFF;
        int cursor = -1;
        for (unsigned int i=0; i<track_count; i++) {
            if (cursors[i].m_Locator.m_SampleTable &&
                cursors[i].m_Locator.m_Sample.GetOffset() <= min_offset) {
                    min_offset = cursors[i].m_Locator.m_Sample.GetOffset();
                    cursor = i;
            }
        }

        // stop if all cursors are exhausted
        if (cursor == -1) break;

        // append this locator to the layout list
        AP4_SampleLocator& locator = cursors[cursor].m_Locator;
        locators.Append(locator);
        //AP4_Debug("NEXT: track %d, sample %d:%d: offset=%d, size=%d\n",
        //    locator.m_TrakIndex, 
        //    locator.m_Chunk,
        //    locator.m_SampleIndex,
        //    locator.m_Sample.GetOffset(),
        //    locator.m_Sample.GetSize());

        // move the cursor to the next sample
        locator.m_SampleIndex++;
        if (locator.m_SampleIndex == locator.m_SampleTable->GetSampleCount()) {
            // mark this track as completed
            locator.m_SampleTable = NULL;
        } else {
            // get the next sample info
            locator.m_SampleTable->GetSample(locator.m_SampleIndex, 
                locator.m_Sample);
            AP4_Ordinal skip, sdesc;
            locator.m_SampleTable->GetChunkForSample(locator.m_SampleIndex+1, // the internal API is 1-based
                locator.m_Chunk,
                skip, sdesc);
        }
    }

    // update the stbl atoms and compute the mdat size
    AP4_Size mdat_size = 0;
    int current_track  = -1;
    int current_chunk  = -1;
    AP4_Offset current_chunk_offset = 0;
    AP4_Size current_chunk_size = 0;
    for (AP4_Ordinal i=0; i<locators.ItemCount(); i++) {
        AP4_SampleLocator& locator = locators[i];
        if ((int)locator.m_TrakIndex != current_track ||
            (int)locator.m_Chunk     != current_chunk) {
            // start a new chunk for this track
            current_chunk_offset += current_chunk_size;
            current_chunk_size = 0;
            current_track = locator.m_TrakIndex;
            current_chunk = locator.m_Chunk;
            locator.m_SampleTable->SetChunkOffset(locator.m_Chunk, 
                current_chunk_offset);
        } 
        AP4_Size sample_size;
        TrackHandler* handler = handlers[locator.m_TrakIndex];
        if (handler) {
            sample_size = handler->GetProcessedSampleSize(locator.m_Sample);
            locator.m_SampleTable->SetSampleSize(locator.m_SampleIndex+1, sample_size);
        } else {
            sample_size = locator.m_Sample.GetSize();
        }
        current_chunk_size += sample_size;
        mdat_size += sample_size;
    }

    // process the tracks (ex: sample descriptions processing)
    for (AP4_Ordinal i=0; i<track_count; i++) {
        TrackHandler* handler = handlers[i];
        if (handler) handler->ProcessTrack();
    }

    // initialize the processor
    Finalize(top_level);

    // calculate the size of all atoms combined
    AP4_Size atoms_size = 0;
    top_level.GetChildren().Apply(AP4_AtomSizeAdder(atoms_size));

    // adjust the chunk offsets
    for (AP4_Ordinal i=0; i<track_count; i++) {
        AP4_TrakAtom* trak;
        trak_atoms.Get(i, trak);
        trak->AdjustChunkOffsets(atoms_size+AP4_ATOM_HEADER_SIZE);
    }

    // write all atoms
    top_level.GetChildren().Apply(AP4_AtomListWriter(output));

    // write mdat header
    output.WriteUI32(mdat_size+AP4_ATOM_HEADER_SIZE);
    output.WriteUI32(AP4_ATOM_TYPE_MDAT);

#if defined(AP4_DEBUG)
    AP4_Offset before;
    output.Tell(before);
#endif

    // write the samples
    AP4_Sample sample;
    AP4_DataBuffer data_in;
    AP4_DataBuffer data_out;
    for (unsigned int i=0; i<locators.ItemCount(); i++) {
        AP4_SampleLocator& locator = locators[i];
        locator.m_Sample.ReadData(data_in);
        TrackHandler* handler = handlers[locator.m_TrakIndex];
        if (handler) {
            handler->ProcessSample(data_in, data_out);
            output.Write(data_out.GetData(), data_out.GetDataSize());
        } else {
            output.Write(data_in.GetData(), data_in.GetDataSize());            
        }
    }

#if defined(AP4_DEBUG)
    AP4_Offset after;
    output.Tell(after);
    AP4_ASSERT(after-before == mdat_size);
#endif

    // cleanup
    delete[] cursors;
    for (unsigned int i=0; i<track_count; i++) {
        delete handlers[i];
    }
    delete[] handlers;

    return AP4_SUCCESS;
}