Trick-mode processing for digital video
A method for processing digital video data intended for normal mode display to obtain corresponding digital video data for trick-mode display includes modifying the normal mode digital video data to achieve a substantially uniform delivery rate to a video client. This results in smoother trick-mode playback. The modified normal mode digital video data is saved as a trick-mode file. When trick-mode playback is requested, a video-server retrieves data from the trick-mode file.
1. A method for processing digital video data for trick-mode display, said digital video data having an ordered sequence of frames, said method comprising:
specifying a range of delivery intervals;
selecting a set of frames from said ordered sequence of frames, each frame in said selected set including data representative of a selected image and associated with a corresponding delivery interval; and
for each frame in the selected set, generating a modified frame for trick-mode display according to whether the corresponding delivery interval of said selected frame is less than a lower bound of the range or greater than an upper bound of the range, said modified frame including data representative of said selected image modified for delivery at a delivery interval within said range of delivery intervals.
2. The method of claim 1 further comprising including said modified frame in a sequence of modified frames to be displayed in trick-mode.
3. The method of claim 2 further comprising saving said sequence of modified frames in a trick-file.
4. The method of claim 3 wherein saving said sequence comprises saving said trick-file in a mass-storage subsystem.
5. The method of claim 4 further comprising selecting said mass-storage subsystem from a group consisting of: a magnetic disk, an optical disk, and a magnetic tape.
6. The method of claim 3 wherein said digital video file is an MPEG file and saving said sequence of modified frames in a trick-file comprises interleaving said modified frames with frames specifying zero motion.
7. The method of claim 2 further comprising transmitting said sequence of modified frames to a video client.
8. The method of claim 1 wherein generating a modified frame comprises
specifying a range of frame sizes on the basis of said specified range of delivery intervals; and
processing said data representative of said selected image to create a modified frame having a modified-frame size within said range of frame sizes.
9. The method of claim 8 wherein processing said data representative of said selected image comprises padding said data to enable said modified-frame size to be within said specified range of frame sizes.
10. The method of claim 9 wherein padding said data comprises adding null packets to said data.
11. The method of claim 8 wherein processing said data representative of said selected image comprises degrading said data representative of said selected image such that said modified frame size is less than an upper bound of said range of frame sizes.
12. The method of claim 11 wherein degrading comprises discarding selected high frequency coefficients from said data representative of said selected image.
13. The method of claim 11 wherein degrading comprises changing a quantizer scale associated with said data representative of said selected image.
14. The method of claim 11 wherein degrading comprises
selecting a first portion of said selected image;
selecting a second portion of said selected image; and
degrading data representative of said first portion differently from data representative of said second portion.
15. The method of claim 14 further comprising selecting said second portion to be a central portion of said selected frame and selecting said first portion to be a peripheral portion of said selected frame.
16. The method of claim 1 further comprising selecting said digital video file to be an MPEG file.
17. The method of claim 16 further comprising selecting said ordered sequence of frames to be a sequence of intra-coded frames.
18. The method of claim 1 further comprising selecting said digital video file to include an image encoded by a wavelet transform.
19. The method of claim 1 wherein said selected frame includes interlaced video data and said method further comprises removing said interlaced data.
20. The method of claim 19 wherein removing said interlaced video data from said frame comprises overwriting a second field of said frame with a first field of said frame.
21. The method of claim 1 further comprising indexing said modified frame to said selected frame thereby enabling transition between a normal mode, in which data representative of said image is obtained from said selected frame, and a trick-mode in which data representative of said image is obtained from said modified frame.
22. The method of claim 1 wherein said range of delivery intervals is a range of substantially equal delivery intervals.
23. Computer-readable media having encoded thereon software for processing digital video data for trick-mode display, said software including instructions for causing a computer to:
receive a range of delivery intervals;
select a set of frames from an ordered sequence of frames from said digital video data, each frame in said selected set being associated with a corresponding delivery interval; and
for each frame in the selected set, generate a modified frame for trick-mode display according to whether the corresponding delivery interval of said selected frame is less than a lower bound of the range or greater than an upper bound of the range, said modified frame including data representative of said selected image modified for delivery at a delivery interval within said range of delivery intervals.
24. The computer-readable media of claim 23 wherein said range of delivery intervals is a range of substantially equal delivery intervals.