MovieVideoChart

This sample code demonstrates direct access to video samples in movie

files using the new, B-frame-aware APIs in QuickTime 7.  

Requires: Mac OS X 10.4. Xcode 2.1 and later projects build universal binary.

To use this sample, open a movie in the MovieVideoChart application.  

A window will appear containing a scrolling chart showing the internal 

structure of the movie's video track.  The horizontal scroll bar lets 

you browse through time; a slider in the lower left corner lets you 

adjust the magnification.

At the bottom of the window, the frames in the media are displayed in 

decode order; above that is their permutation into display order, if any;

above that is any rearrangement due to track edits.

To gather information about many samples at once (in this case, to 

draw the decode-to-display reordering), the application uses 

CopyMediaMutableSampleTable, which returns a QTSampleTable, which is

a CF-style object that holds information about samples.  

To gather information about a single sample, and to read it into memory

(to draw the thumbnails), the application uses GetMediaSample2.

To render the frames as thumbnails, the application uses 

ICMDecompressionSessions.  Care must be taken to ensure that frames 

are decompressed in correct decode order, walking forward from the 

previous key frame when appropriate.

In many cases, it is not necessary to reach down to these low-level APIs.

You can use QTOpenGLTextureContexts and QTPixelBufferVisualContexts to

render frames from movies without needing to deal with the complexities 

of B frames and inter-frame dependencies.