C / C++ / MFC

ffmpeg -i SampleVideo_1280x720_1mb.mp4 -vcodec copy -acodec copy
-encryption_scheme cenc-aes-ctr -encryption_key
76a6c65c5ea762046bd749a2e632ccbb -encryption_kid
a7e61c373e219033c21091fa607bf3b8 SampleVideo_1280x720_1mb_encrypted.mp4

ffplay SampleVideo_1280x720_1mb_encrypted.mp4 -decryption_key
76a6c65c5ea762046bd749a2e632ccbb

typedef void (*readDataResultCallback_t)(uint8_t* readData, uint16_t sizeOfReadData);

typedef enum {
    STATE1 = 0,
    STATE2 = 1,
    STATE3 = 2,
} stateMachineState_e;

typedef struct __attribute__((__packed__)) {
    stateMachineState_e      state;
    uint32_t                 startAddr;
    uint16_t                 numRegsToRead;
    readDataResultCallback_t readDataResultCallback;
} stateMachineStep_s;

static stateMachineState_e state = STATE1;

stateMachineStep_s stateMachineSteps[3] = {
    {STATE1,    10, 2, { (uint8_t* readData, uint16_t sizeOfReadData) {
                         if (stringCompare(readData, "AB") {
                             ... Do stuff here...
                             state = STATE_2;
                         } else {
                             ... Do stuff here...
                             state = STATE_3;
                         }}},
    {STATE2,    20, 3, { (uint8_t* readData, uint16_t sizeOfReadData) {
                         if (stringCompare(readData, "ABC") {
                             ... Do stuff here...
                             state = STATE_1;
                         } else {
                             ... Do stuff here...
                             state = STATE_3;
                         }}},
    {STATE3,    30,  4, { (uint8_t* readData, uint16_t sizeOfReadData) {
                          if (stringCompare(readData, "ABCD") {
                              ... Do stuff here...
                               state = STATE_3;
                          } else {
                              ... Do stuff here...
                              state = STATE_2;
                          }}},
};