Method SeekTo

src/core/videosource.cpp:803–848

}

bool FFMS_VideoSource::SeekTo(int n, int SeekOffset) {
    bool ForceSeek = false;
    if (Stage == DecodeStage::INITIALIZE_SOURCE) {
        ForceSeek = true;
        Stage = DecodeStage::INITIALIZE;
    }

    // The semantics here are basically "return true if we don't know exactly where our seek ended up (destination isn't frame 0)"
    if (SeekMode >= 0) {
        int TargetFrame = n + SeekOffset;
        if (TargetFrame < 0)
            throw FFMS_Exception(FFMS_ERROR_SEEKING, FFMS_ERROR_UNKNOWN,
                "Frame accurate seeking is not possible in this file");

        // Seeking too close to the end of the stream can result in a different decoder delay since
        // frames are returned as soon as draining starts, so avoid this to keep the delay predictable.
        // Is the +1 necessary here? Not sure, but let's keep it to be safe.
        int EndOfStreamDist = CodecContext->has_b_frames + 1;

        if (CodecContext->codec_id == AV_CODEC_ID_H264)
            // Work around a bug in ffmpeg's h264 decoder where frames are skipped when seeking too
            // close to the end in open-gop files: https://trac.ffmpeg.org/ticket/10936
            EndOfStreamDist *= 2;

        TargetFrame = std::min(TargetFrame, Frames.RealFrameNumber(std::max(0, VP.NumFrames - 1 - EndOfStreamDist)));

        if (SeekMode < 3)
            TargetFrame = Frames.FindClosestVideoKeyFrame(TargetFrame);

        if (SeekMode == 0) {
            if (n < CurrentFrame) {
                Seek(Frames[0].OriginalPos);
            }
        } else {
            // 10 frames is used as a margin to prevent excessive seeking since the predicted best keyframe isn't always selected by avformat
            if (ForceSeek || n < CurrentFrame || TargetFrame > CurrentFrame + 10 || (SeekMode == 3 && n > CurrentFrame + 10)) {
                Seek(TargetFrame);
                return true;
            }
        }
    } else if (n < CurrentFrame) {
        throw FFMS_Exception(FFMS_ERROR_SEEKING, FFMS_ERROR_INVALID_ARGUMENT,
            "Non-linear access attempted");
    }
    return false;
}

FFMS_Frame *FFMS_VideoSource::GetFrame(int n) {
    GetFrameCheck(n);