OggReader.cc

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#include "OggReader.hh"
#include "MSXException.hh"
#include "yuv2rgb.hh"
#include "CliComm.hh"
#include "MemoryOps.hh"
#include "narrow.hh"
#include "one_of.hh"
#include "ranges.hh"
#include "stringsp.hh" // for strncasecmp
#include "view.hh"
#include "xrange.hh"
#include <cstdlib> // for atoi
#include <cctype> // for isspace
#include <memory>
 
// TODO
// - Improve error handling
// - When an non-ogg file is passed, the entire file is scanned
// - Clean up this mess!
namespace openmsx {
 
Frame::Frame(const th_ycbcr_buffer& yuv)
{
        unsigned y_size  = yuv[0].height * yuv[0].stride;
        unsigned uv_size = yuv[1].height * yuv[1].stride;
 
        buffer[0] = yuv[0];
        buffer[0].data = static_cast<unsigned char*>(
                        MemoryOps::mallocAligned(16, y_size));
        buffer[1] = yuv[1];
        buffer[1].data = static_cast<unsigned char*>(
                        MemoryOps::mallocAligned(16, uv_size));
        buffer[2] = yuv[2];
        buffer[2].data = static_cast<unsigned char*>(
                        MemoryOps::mallocAligned(16, uv_size));
}
 
Frame::~Frame()
{
        MemoryOps::freeAligned(buffer[0].data);
        MemoryOps::freeAligned(buffer[1].data);
        MemoryOps::freeAligned(buffer[2].data);
}
 
 
OggReader::OggReader(const Filename& filename, CliComm& cli_)
        : cli(cli_)
        , file(filename)
        , fileSize(file.getSize())
{
        th_info ti;
        th_comment tc;
        th_setup_info* tsi = nullptr;
 
        th_info_init(&ti);
        th_comment_init(&tc);
 
        vorbis_info_init(&vi);
        vorbis_comment_init(&vc);
 
        ogg_sync_init(&sync);
 
        ogg_page page;
 
        try {
                while ((audioHeaders || !theora) && nextPage(&page)) {
                        int serial = ogg_page_serialno(&page);
 
                        if (serial == audioSerial) {
                                vorbisHeaderPage(&page);
                                continue;
                        } else if (serial == videoSerial) {
                                theoraHeaderPage(&page, ti, tc, tsi);
                                continue;
                        } else if (serial == skeletonSerial) {
                                continue;
                        }
 
                        if (!ogg_page_bos(&page)) {
                                if (videoSerial == -1) {
                                        throw MSXException("No video track found");
                                }
 
                                if (audioSerial == -1) {
                                        throw MSXException("No audio track found");
                                }
 
                                // This should be unreachable, right?
                                continue;
                        }
 
                        ogg_stream_state stream;
                        ogg_packet packet;
 
                        ogg_stream_init(&stream, serial);
                        ogg_stream_pagein(&stream, &page);
                        if (ogg_stream_packetout(&stream, &packet) <= 0) {
                                ogg_stream_clear(&stream);
                                throw MSXException("Invalid header");
                        }
 
                        if (packet.bytes < 8) {
                                ogg_stream_clear(&stream);
                                throw MSXException("Header to small");
                        }
 
                        if (ranges::equal(std::span{packet.packet, 7}, std::array<uint8_t, 7>{1, 'v', 'o', 'r', 'b', 'i', 's'})) {
                                if (audioSerial != -1) {
                                        ogg_stream_clear(&stream);
                                        throw MSXException("Duplicate audio stream");
                                }
 
                                audioSerial = serial;
                                ogg_stream_init(&vorbisStream, serial);
 
                                vorbisHeaderPage(&page);
 
                        } else if (ranges::equal(std::span{packet.packet, 7}, std::array<uint8_t, 7>{128, 't', 'h', 'e', 'o', 'r', 'a'})) {
                                if (videoSerial != -1) {
                                        ogg_stream_clear(&stream);
                                        throw MSXException("Duplicate video stream");
                                }
 
                                videoSerial = serial;
                                ogg_stream_init(&theoraStream, serial);
 
                                theoraHeaderPage(&page, ti, tc, tsi);
 
                        } else if (ranges::equal(std::span{packet.packet, 8}, std::array<uint8_t, 8>{'f', 'i', 's', 'h', 'e', 'a', 'd', 0})) {
                                skeletonSerial = serial;
 
                        } else if (ranges::equal(std::span{packet.packet, 4}, std::array<uint8_t, 4>{'B', 'B', 'C', 'D'})) {
                                ogg_stream_clear(&stream);
                                throw MSXException("DIRAC not supported");
 
                        } else if (ranges::equal(std::span{packet.packet, 5}, std::array<uint8_t, 5>{127, 'F', 'L', 'A', 'C'})) {
                                ogg_stream_clear(&stream);
                                throw MSXException("FLAC not supported");
 
                        } else  {
                                ogg_stream_clear(&stream);
                                throw MSXException("Unknown stream in ogg file");
                        }
 
                        ogg_stream_clear(&stream);
                }
 
                if (videoSerial == -1) {
                        throw MSXException("No video track found");
                }
 
                if (audioSerial == -1) {
                        throw MSXException("No audio track found");
                }
 
                if (vi.channels != 2) {
                        throw MSXException("Audio must be stereo");
                }
 
                if (ti.frame_width != 640 || ti.frame_height != 480) {
                        throw MSXException("Video must be size 640x480");
                }
 
                if (ti.fps_numerator == 30000 && ti.fps_denominator == 1001) {
                        frameRate = 30;
                } else if (ti.fps_numerator == 60000 && ti.fps_denominator == 1001) {
                        frameRate = 60;
                } else {
                        throw MSXException("Video frame rate must be 59.94Hz or 29.97Hz");
                }
 
                // FIXME: Support YUV444 before release
                // It would be much better to use YUV444, however the existing
                // captures are in YUV420 format. yuv2rgb will have to be
                // updated too.
                if (ti.pixel_fmt != TH_PF_420) {
                        throw MSXException("Video must be YUV420");
                }
        } catch (MSXException&) {
                th_setup_free(tsi);
                th_info_clear(&ti);
                th_comment_clear(&tc);
                cleanup();
                throw;
        }
 
        th_setup_free(tsi);
        th_info_clear(&ti);
        th_comment_clear(&tc);
}
 
void OggReader::cleanup()
{
        if (audioHeaders == 0) {
                vorbis_dsp_clear(&vd);
                vorbis_block_clear(&vb);
        }
 
        th_decode_free(theora);
 
        vorbis_info_clear(&vi);
        vorbis_comment_clear(&vc);
        if (audioSerial != -1) {
                ogg_stream_clear(&vorbisStream);
        }
 
        if (videoSerial != -1) {
                ogg_stream_clear(&theoraStream);
        }
 
        ogg_sync_clear(&sync);
}
 
OggReader::~OggReader()
{
        cleanup();
}
 
void OggReader::vorbisFoundPosition()
{
        auto last = vorbisPos;
        for (auto& audioFrag : view::reverse(audioList)) {
                last -= audioFrag->length;
                audioFrag->position = last;
        }
 
        // last is now the first vorbis audio decoded
        if (last > currentSample) {
                cli.printWarning("missing part of audio stream");
        }
 
        if (vorbisPos > currentSample) {
                currentSample = vorbisPos;
        }
}
 
 
void OggReader::vorbisHeaderPage(ogg_page* page)
{
        ogg_stream_pagein(&vorbisStream, page);
 
        while (true) {
                ogg_packet packet;
 
                int res = ogg_stream_packetout(&vorbisStream, &packet);
                if (res < 0) {
                        throw MSXException("error in vorbis stream");
                }
                if (res == 0) break;
 
                if (audioHeaders == 0) {
                        // ignore, we'll seek to the beginning again before playing
                        continue;
                }
 
                if (packet.packetno <= 2) {
                        if (vorbis_synthesis_headerin(&vi, &vc, &packet) < 0) {
                                throw MSXException("invalid vorbis header");
                        }
                        --audioHeaders;
                }
 
                if (packet.packetno == 2) {
                        vorbis_synthesis_init(&vd, &vi) ;
                        vorbis_block_init(&vd, &vb);
                }
        }
}
 
void OggReader::theoraHeaderPage(ogg_page* page, th_info& ti, th_comment& tc,
                                 th_setup_info*& tsi)
{
        ogg_stream_pagein(&theoraStream, page);
 
        while (true) {
                ogg_packet packet;
 
                int res = ogg_stream_packetout(&theoraStream, &packet);
                if (res < 0) {
                        throw MSXException("error in vorbis stream");
                }
                if (res == 0) break;
 
                if (theora) {
                        // ignore, we'll seek to the beginning again before playing
                        continue;
                }
 
                if (packet.packetno <= 2) {
                        res = th_decode_headerin(&ti, &tc, &tsi, &packet);
                        if (res <= 0) {
                                throw MSXException("invalid theora header");
                        }
                }
 
                if (packet.packetno == 2) {
                        theora = th_decode_alloc(&ti, tsi);
                        readMetadata(tc);
                        granuleShift = ti.keyframe_granule_shift;
                }
        }
}
 
void OggReader::readVorbis(ogg_packet* packet)
{
        // deal with header packets
        if (packet->packetno <= 2) [[unlikely]] {
                return;
        }
 
        if (state == FIND_LAST) {
                if (packet->granulepos != -1) {
                        if ((currentSample == AudioFragment::UNKNOWN_POS) ||
                            (size_t(packet->granulepos) > currentSample)) {
                                currentSample = packet->granulepos;
                        }
                }
                return;
 
        } else if (state == FIND_FIRST) {
                if (packet->granulepos != -1 &&
                                currentSample == AudioFragment::UNKNOWN_POS) {
                        currentSample = packet->granulepos;
                }
                return;
 
        } else if (state == FIND_KEYFRAME) {
                // Not relevant for vorbis
                return;
        }
 
        // generate pcm
        if (vorbis_synthesis(&vb, packet) != 0) {
                return;
        }
 
        vorbis_synthesis_blockin(&vd, &vb);
 
        float** pcm;
        int decoded = vorbis_synthesis_pcmout(&vd, &pcm);
        int pos = 0;
 
        while (pos < decoded)  {
                // Find memory to copy PCM into
                if (recycleAudioList.empty()) {
                        auto audio = std::make_unique<AudioFragment>();
                        audio->length = 0;
                        recycleAudioList.push_back(std::move(audio));
                }
                auto& audio = recycleAudioList.front();
                if (audio->length == 0) {
                        audio->position = vorbisPos;
                } else {
                        // first element was already partially filled
                }
 
                // Copy PCM
                auto len = std::min(decoded - pos,
                                    narrow<int>(AudioFragment::MAX_SAMPLES - audio->length));
 
                ranges::copy(std::span{&pcm[0][pos], size_t(len)}, &audio->pcm[0][audio->length]);
                ranges::copy(std::span{&pcm[1][pos], size_t(len)}, &audio->pcm[1][audio->length]);
                audio->length += len;
                pos += len;
 
                // Last packet or found position after seeking?
                bool last = (decoded == pos && (packet->e_o_s ||
                                 (vorbisPos == AudioFragment::UNKNOWN_POS &&
                                  packet->granulepos != -1)));
 
                if (vorbisPos != AudioFragment::UNKNOWN_POS) {
                        vorbisPos += len;
                        currentSample += len;
                }
 
                if (audio->length == AudioFragment::MAX_SAMPLES || last) {
                        audioList.push_back(recycleAudioList.pop_front());
                }
        }
 
        // The granulepos is the no. of samples since the beginning of the
        // stream. Only once per ogg page is this populated.
        if (packet->granulepos != -1) {
                if (vorbisPos == AudioFragment::UNKNOWN_POS) {
                        vorbisPos = packet->granulepos;
                        vorbisFoundPosition();
                } else {
                        if (vorbisPos != size_t(packet->granulepos)) {
                                cli.printWarning(
                                        "vorbis audio out of sync, expected ",
                                        vorbisPos, ", got ", packet->granulepos);
                                vorbisPos = packet->granulepos;
                        }
                }
        }
 
        // done with PCM data
        vorbis_synthesis_read(&vd, decoded);
}
 
size_t OggReader::frameNo(ogg_packet* packet) const
{
        if (packet->granulepos == -1) {
                return size_t(-1);
        }
 
        size_t intra = packet->granulepos & ((size_t(1) << granuleShift) - 1);
        size_t key = packet->granulepos >> granuleShift;
        return key + intra;
}
 
void OggReader::readMetadata(th_comment& tc)
{
        char* metadata = nullptr;
        for (auto i : xrange(tc.comments)) {
                if (!strncasecmp(tc.user_comments[i], "location=",
                                 strlen("location="))) {
                        metadata = tc.user_comments[i] + strlen("location=");
                        break;
                }
        }
        if (!metadata) {
                return;
        }
 
        // Maybe there is a better way of doing this parsing in C++
        char* p = metadata;
        while (p) {
                while (isspace(*p)) {
                        p++;
                }
                if (strncasecmp(p, "chapter: ", 9) == 0) {
                        int chapter = atoi(p + 9);
                        p = strchr(p, ',');
                        if (!p) break;
                        ++p;
                        size_t frame = atol(p);
                        if (frame) {
                                chapters.emplace_back(ChapterFrame{chapter, frame});
                        }
                } else if (strncasecmp(p, "stop: ", 6) == 0) {
                        size_t stopFrame = atol(p + 6);
                        if (stopFrame) {
                                stopFrames.push_back(stopFrame);
                        }
                }
                p = strchr(p, '\n');
                if (p) ++p;
        }
        ranges::sort(stopFrames);
        ranges::sort(chapters, {}, &ChapterFrame::chapter);
}
 
void OggReader::readTheora(ogg_packet* packet)
{
        if (th_packet_isheader(packet)) {
                return;
        }
 
        size_t frameno = frameNo(packet);
 
        // If we're seeking, we're only interested in packets with
        // frame numbers
        if ((state != PLAYING) && (frameno == size_t(-1))) {
                return;
        }
 
        if (state == FIND_LAST) {
                if ((currentFrame == size_t(-1)) || (currentFrame < frameno)) {
                        currentFrame = frameno;
                }
                return;
 
        } else if (state == FIND_FIRST) {
                if ((currentFrame == size_t(-1)) || (currentFrame > frameno)) {
                        currentFrame = frameno;
                }
                return;
 
        } else if (state == FIND_KEYFRAME) {
                if (frameno < currentFrame) {
                        keyFrame = packet->granulepos >> granuleShift;
                } else if (currentFrame == frameno) {
                        keyFrame = packet->granulepos >> granuleShift;
                        currentSample = 1;
                } else if (frameno > currentFrame) {
                        currentSample = 1;
                }
                return;
        }
 
        if ((keyFrame != size_t(-1)) && (frameno != size_t(-1)) &&
            (frameno < keyFrame)) {
                // We're reading before the keyframe, discard
                return;
        }
 
        if (packet->bytes == 0 && frameList.empty()) {
                // No use passing empty packets (which represent dup frame)
                // before we've read any frame.
                return;
        }
 
        keyFrame = size_t(-1);
 
        int rc = th_decode_packetin(theora, packet, nullptr);
        switch (rc) {
        case TH_DUPFRAME:
                if (frameList.empty()) {
                        cli.printWarning("Theora error: dup frame encountered "
                                         "without preceding frame");
                } else {
                        frameList.back()->length++;
                }
                break;
        case TH_EIMPL:
                cli.printWarning("Theora error: not capable of reading this");
                break;
        case TH_EFAULT:
                cli.printWarning("Theora error: API not used correctly");
                break;
        case TH_EBADPACKET:
                cli.printWarning("Theora error: bad packet");
                break;
        case 0:
                break;
        default:
                cli.printWarning("Theora error: unknown error ", rc);
                break;
        }
 
        if (rc) {
                return;
        }
 
        th_ycbcr_buffer yuv;
 
        if (th_decode_ycbcr_out(theora, yuv) != 0) {
                return;
        }
 
        if ((frameno != size_t(-1)) && (frameno < currentFrame)) {
                return;
        }
 
        currentFrame = frameno + 1;
 
        std::unique_ptr<Frame> frame;
        if (recycleFrameList.empty()) {
                frame = std::make_unique<Frame>(yuv);
        } else {
                frame = std::move(recycleFrameList.back());
                recycleFrameList.pop_back();
        }
 
        size_t y_size  = yuv[0].height * size_t(yuv[0].stride);
        size_t uv_size = yuv[1].height * size_t(yuv[1].stride);
        ranges::copy(std::span{yuv[0].data,  y_size}, frame->buffer[0].data);
        ranges::copy(std::span{yuv[1].data, uv_size}, frame->buffer[1].data);
        ranges::copy(std::span{yuv[2].data, uv_size}, frame->buffer[2].data);
 
        // At lot of frames have frame number -1, only some have the correct
        // frame number. We continue counting from the previous known
        // postion
        Frame* last = frameList.empty() ? nullptr : frameList.back().get();
        if (last && (last->no != size_t(-1))) {
                if (frameno != one_of(size_t(-1), last->no + last->length)) {
                        cli.printWarning("Theora frame sequence wrong");
                } else {
                        frameno = last->no + last->length;
                }
        }
 
        frame->no = frameno;
        frame->length = 1;
 
        // We may read some frames before we encounter one with a proper
        // frame number. When we do, go back and populate the frame
        // numbers correctly
        if (!frameList.empty() && (frameno != size_t(-1)) &&
            (frameList[0]->no == size_t(-1))) {
                for (auto& frm : view::reverse(frameList)) {
                        frameno -= frm->length;
                        frm->no = frameno;
                }
        }
 
        frameList.push_back(std::move(frame));
}
 
void OggReader::getFrameNo(RawFrame& rawFrame, size_t frameno)
{
        Frame* frame;
        while (true) {
                // If there are no frames or the frames we have read
                // does not include a proper frame number, just read
                // more data
                if (frameList.empty() || (frameList[0]->no == size_t(-1))) {
                        if (!nextPacket()) {
                                return;
                        }
                        continue;
                }
 
                // Remove unneeded frames. Note that at 60Hz the odd and
                // and even frame are displayed during still, so we can
                // only throw away the one two frames ago
                while (frameList.size() >= 3 && frameList[2]->no <= frameno) {
                        recycleFrameList.push_back(frameList.pop_front());
                }
 
                if (!frameList.empty() && frameList[0]->no > frameno) {
                        // we're missing frames!
                        frame = frameList[0].get();
                        cli.printWarning(
                                        "Cannot find frame ", frameno, " using ",
                                frame->no, " instead");
                        break;
                }
 
                if ((frameList.size() >= 2) &&
                    ((frameno >= frameList[0]->no) &&
                     (frameno <  frameList[1]->no))) {
                        frame = frameList[0].get();
                        break;
                }
 
                if ((frameList.size() >= 3) &&
                    ((frameno >= frameList[1]->no) &&
                     (frameno <  frameList[2]->no))) {
                        frame = frameList[1].get();
                        break;
                }
 
                // Sanity check, should not happen
                if (frameList.size() > (size_t(2) << granuleShift)) {
                        // We've got more than twice as many frames
                        // as the maximum distance between key frames.
                        cli.printWarning("Cannot find frame ", frameno);
                        return;
                }
 
                // ..add read some new ones
                if (!nextPacket()) {
                        return;
                }
        }
 
        yuv2rgb::convert(frame->buffer, rawFrame);
}
 
void OggReader::recycleAudio(std::unique_ptr<AudioFragment> audio)
{
        audio->length = 0;
        recycleAudioList.push_back(std::move(audio));
}
 
const AudioFragment* OggReader::getAudio(size_t sample)
{
        // Read while position is unknown
        while (audioList.empty() ||
               audioList.front()->position == AudioFragment::UNKNOWN_POS) {
                if (!nextPacket()) {
                        return nullptr;
                }
        }
 
        auto it = begin(audioList);
        while (true) {
                auto& audio = *it;
                if (audio->position + audio->length + getSampleRate() <= sample) {
                        // Dispose if this, more than 1 second old
                        recycleAudio(std::move(*it));
                        it = audioList.erase(it);
                } else if (audio->position + audio->length <= sample) {
                        ++it;
                } else {
                        if (audio->position <= sample) {
                                return audio.get();
                        } else {
                                // gone too far?
                                return nullptr;
                        }
                }
 
                // read more if we're at the end of the list
                if (it == end(audioList)) {
                        size_t size = audioList.size();
                        while (size == audioList.size()) {
                                if (!nextPacket()) {
                                        return nullptr;
                                }
                        }
 
                        // reset the iterator to not point to the end
                        it = begin(audioList);
                }
        }
}
 
bool OggReader::nextPacket()
{
        ogg_packet packet;
        ogg_page page;
 
        while (true) {
                int ret = ogg_stream_packetout(&vorbisStream, &packet);
                if (ret == 1) {
                        readVorbis(&packet);
                        return true;
                } else if (ret == -1) {
                        // recoverable error
                        continue;
                }
 
                ret = ogg_stream_packetout(&theoraStream, &packet);
                if (ret == 1) {
                        readTheora(&packet);
                        return true;
                } else if (ret == -1) {
                        // recoverable error
                        continue;
                }
 
                if (!nextPage(&page)) {
                        return false;
                }
 
                int serial = ogg_page_serialno(&page);
                if (serial == audioSerial) {
                        if (ogg_stream_pagein(&vorbisStream, &page)) {
                                cli.printWarning("Failed to submit vorbis page");
                        }
                } else if (serial == videoSerial) {
                        if (ogg_stream_pagein(&theoraStream, &page)) {
                                cli.printWarning("Failed to submit theora page");
                        }
                } else if (serial != skeletonSerial) {
                        cli.printWarning("Unexpected stream with serial ",
                                         serial, " in ogg file");
                }
        }
}
 
 
bool OggReader::nextPage(ogg_page* page)
{
        static constexpr size_t CHUNK = 4096;
 
        long ret;
        while ((ret = ogg_sync_pageseek(&sync, page)) <= 0) {
                if (ret < 0) {
                        //throw MSXException("Invalid Ogg file");
                }
 
                size_t chunk;
                if (fileSize - fileOffset >= CHUNK) {
                        chunk = CHUNK;
                } else if (fileOffset < fileSize) {
                        chunk = fileSize - fileOffset;
                } else {
                        return false;
                }
 
                char* buffer = ogg_sync_buffer(&sync, long(chunk));
                file.read(std::span{buffer, chunk});
                fileOffset += chunk;
 
                if (ogg_sync_wrote(&sync, long(chunk)) == -1) {
                        cli.printWarning("Internal error: ogg_sync_wrote failed");
                }
        }
 
        return true;
}
 
size_t OggReader::bisection(
        size_t frame, size_t sample,
        size_t maxOffset, size_t maxSamples, size_t maxFrames)
{
        // Defined to be a power-of-two such that the calculations can be done faster.
        // Note that the sample-number is in the range of: 1..(44100*60*60)
        constexpr uint64_t SHIFT = 0x20000000ull;
 
        uint64_t offsetA = 0, offsetB = maxOffset;
        uint64_t sampleA = 0, sampleB = maxSamples;
        uint64_t frameA = 1, frameB = maxFrames;
 
        while (true) {
                uint64_t ratio = (frame - frameA) * SHIFT / (frameB - frameA);
                if (ratio < 5) {
                        return offsetA;
                }
 
                uint64_t frameOffset = ratio * (offsetB - offsetA) / SHIFT + offsetA;
                ratio = (sample - sampleA) * SHIFT / (sampleB - sampleA);
                if (ratio < 5) {
                        return offsetA;
                }
                uint64_t sampleOffset = ratio * (offsetB - offsetA) / SHIFT + offsetA;
                auto offset = std::min(sampleOffset, frameOffset);
 
                file.seek(offset);
                fileOffset = offset;
                ogg_sync_reset(&sync);
                currentFrame = size_t(-1);
                currentSample = AudioFragment::UNKNOWN_POS;
                state = FIND_FIRST;
 
                while (((currentFrame == size_t(-1)) ||
                        (currentSample == AudioFragment::UNKNOWN_POS)) &&
                       nextPacket()) {
                        // continue reading
                }
 
                state = PLAYING;
 
                if (currentSample > sample || currentFrame > frame) {
                        offsetB = offset;
                        sampleB = currentSample;
                        frameB = currentFrame;
                } else if (currentSample + getSampleRate() < sample &&
                                currentFrame + 64 < frame) {
                        offsetA = offset;
                        sampleA = currentSample;
                        frameA = currentFrame;
                } else {
                        return offset;
                }
        }
}
 
size_t OggReader::findOffset(size_t frame, size_t sample)
{
        static constexpr size_t STEP = 32 * 1024;
 
        // first calculate total length in bytes, samples and frames
 
        // The file might have changed since we last requested its size,
        // we assume that only data will be added to it and the ogg streams
        // are exactly as before
        fileSize = file.getSize();
        auto offset = fileSize - 1;
 
        while (offset > 0) {
                if (offset > STEP) {
                        offset -= STEP;
                } else {
                        offset = 0;
                }
 
                file.seek(offset);
                fileOffset = offset;
                ogg_sync_reset(&sync);
                currentFrame = size_t(-1);
                currentSample = AudioFragment::UNKNOWN_POS;
                state = FIND_LAST;
 
                while (nextPacket()) {
                        // continue reading
                }
 
                state = PLAYING;
 
                if ((currentFrame != size_t(-1)) &&
                    (currentSample != AudioFragment::UNKNOWN_POS)) {
                        break;
                }
        }
 
        totalFrames = currentFrame;
 
        // If we're close to beginning, don't bother searching for it,
        // just start at the beginning (arbitrary boundary of 1 second).
        if (sample < getSampleRate() || frame <= 30) {
                keyFrame = 1;
                return 0;
        }
 
        auto maxOffset = offset;
        auto maxSamples = currentSample;
        auto maxFrames = currentFrame;
 
        if ((sample > maxSamples) || (frame > maxFrames)) {
                sample = maxSamples;
                frame = maxFrames;
        }
 
        offset = bisection(frame, sample, maxOffset, maxSamples, maxFrames);
 
        // Find key frame
        file.seek(offset);
        fileOffset = offset;
        ogg_sync_reset(&sync);
        currentFrame = frame;
        currentSample = 0;
        keyFrame = size_t(-1);
        state = FIND_KEYFRAME;
 
        while (currentSample == 0 && nextPacket()) {
                // continue reading
        }
 
        state = PLAYING;
 
        if (keyFrame == one_of(size_t(-1), frame)) {
                return offset;
        }
 
        return bisection(keyFrame, sample, maxOffset, maxSamples, maxFrames);
}
 
bool OggReader::seek(size_t frame, size_t samples)
{
        // Remove all queued frames
        recycleFrameList.insert(end(recycleFrameList),
                std::move_iterator(begin(frameList)),
                std::move_iterator(end  (frameList)));
        frameList.clear();
 
        // Remove all queued audio
        if (!recycleAudioList.empty()) {
                recycleAudioList.front()->length = 0;
        }
        for (auto& a : audioList) {
                recycleAudio(std::move(a));
        }
        audioList.clear();
 
        fileOffset = findOffset(frame, samples);
        file.seek(fileOffset);
 
        ogg_sync_reset(&sync);
 
        vorbisPos = AudioFragment::UNKNOWN_POS;
        currentFrame = frame;
        currentSample = samples;
 
        vorbis_synthesis_restart(&vd);
 
        return true;
}
 
bool OggReader::stopFrame(size_t frame) const
{
        return ranges::binary_search(stopFrames, frame);
}
 
size_t OggReader::getChapter(int chapterNo) const
{
        auto c = binary_find(chapters, chapterNo, {}, &ChapterFrame::chapter);
        return c ? c->frame : 0;
}
 
} // namespace openmsx