Mac Forum / Programming / Mac Programming / April 2007

I am trying to read pixels from a quicktime movie on windows. I am aparently
loading the movie and creating a matching 32 bit per pixel gworld and
finding an interesting time, but the pixels are white.

I am very new to this and may have overlooked something important. It seems
that everything is fine except the actual pixels.

first I call my own function int error = getMovie("filename.mov", movie,
width, height, duration, frames);
to get the movie handle and its size and duration ect

That returns valid values

Then I call GWorldPtr gworld = createGWorld(width,height,pixMapHandle);

to get a gworld. It is always 32 bit no matter what the movie might
originally is. I need it in that format.

Then I call SetMovieGWorld(movie, gworld, GetGWorldDevice(gworld)); to bind
the movie to the gworld.

Next I call my own function renderNextFrame(movie); which finds the next
interesting time and renders it.. or so I hope.

After all this I et the baseaddress of the pixmap and look at the bytes,
which are all 255.

It is next to impossible (for me) to tell where the error is, but I append
all the code of the sample app, in which I have declared the above mentioned
functions. It would be greatly appresiated if someone would take a quick
look at the code and point out the error.

I _assume_ that the problem is related to locking the pixmap or the setting
of a new time and rendering. When exactly should I lock, and should I not
unlock as well?

-------------------

void main()

{

OSErr errCode = InitializeQTML(0);

EnterMovies();

Movie movie;

int width;

int height;

float duration;

int frames;

int error = getMovie("c:\\a.mov", movie, width, height, duration, frames);

PixMapHandle pixMapHandle;

GWorldPtr gworld = createGWorld(width,height,pixMapHandle);

SetMovieGWorld(movie, gworld, GetGWorldDevice(gworld));

renderNextFrame(movie);

Ptr data = GetPixBaseAddr(pixMapHandle);

for(int i=0;i<100;i++) //just looking at the 25 first pixels

{

unsigned char a = *((unsigned char*)data++);

unsigned char r = *((unsigned char*)data++);

unsigned char g = *((unsigned char*)data++);

unsigned char b = *((unsigned char*)data++);

}

getch();

}

int getMovie(char* fileName, Movie& movie, int& width, int& height, float&
duration, int& frames)

{

FSSpec spec;

short refNumber=0;

OSErr errCode = NativePathNameToFSSpec(fileName, &spec, 0);

if(errCode) return 2;

errCode = OpenMovieFile(&spec,&refNumber, fsRdPerm);

if(errCode) return 3;

errCode = NewMovieFromFile(&movie, refNumber, 0,NULL,0,0);

if(errCode) return 4;

TimeValue tv = GetMovieDuration(movie);

Rect r;

GetMovieBox(movie, &r);

width=r.right;

height=r.bottom;

TimeScale ts = GetMovieTimeScale(movie);//fps

Fixed ffr=GetMoviePreferredRate(movie);

duration = (float)tv/(float)ts;

Track track = GetMovieIndTrackType(movie,1, 'vfrr',
movieTrackCharacteristic);

Media media = GetTrackMedia(track);

frames = GetMediaSampleCount(media);

return 0;

}

GWorldPtr createGWorld(int width, int height, PixMapHandle &pixMapHandle)

{

GWorldPtr gworld;

Rect bounds;

OSErr errCode;

bounds.top = bounds.left = 0;

bounds.right = width;

bounds.bottom = height;

errCode = QTNewGWorld(&gworld,32,&bounds,NULL,NULL,NULL);

if(errCode) return 0;

//clear the first frame.. is this nessesary?

LockPixels(GetGWorldPixMap(gworld));

SetGWorld(gworld,NULL);

Rect rect;

rect.left = rect.top = 0;

rect.right = width;

rect.bottom = height;

EraseRect(&rect);

pixMapHandle = GetGWorldPixMap(gworld);

return gworld;

}

void renderNextFrame(Movie movie)

{

short flags = nextTimeMediaSample;

OSType whichMediaType = 'vide';

//flags |= nextTimeEdgeOK;

TimeValue movieTime=0;

TimeValue duration;

GetMovieNextInterestingTime(movie,

flags,

1,

&whichMediaType,

movieTime,

0,

&movieTime,

&duration);

SetMovieTimeValue(movie,movieTime);

MoviesTask(movie,0);

}