Offspeed playback in a video editing system of video data compressed using long groups of pictures

• US 20070133951A1
• Filed: 12/09/2005
• Published: 06/14/2007
• Est. Priority Date: 12/09/2005
• Status: Active Grant

• Current Assignee: Avid Technology Incorporated
• Original Assignee: Avid Technology Incorporated
• Inventors: Flecchia, Mark
• Granted Patent: US 8,300,701 B2
• Time in Patent Office: Days
• US Class Current: 386/346
• CPC Class Codes: G11B 27/005 Reproducing at a different information rate from the information rate of recording for television signals H04N5/783
• CPC Class Codes: G11B 27/034 on discs G11B27/036, G11B27/038 take precedence
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder

Abstract

An editing system handles offspeed and full speed playback of long GOP compressed video information by having one decoder for full-speed or slower forward playback of long GOP compressed motion video information, and a second single-frame, stateless decoder for use for off-speed playback. When compressed data is read from a file, the compressed data for at least one complete group of pictures is read into a buffer, herein called a compressed data buffer. A data structure, herein called a frame ring, is constructed to describe each image in the compressed data buffer. The single-frame, stateless decoder receives decompression parameters in addition to the compressed data for each image from this buffer. If the compressed data is a B-frame or P-frame, then uncompressed data for any other images (i.e., reference frames) required by the decoder to decompress the frame also is input to the single-frame, stateless decoder. If the uncompressed data for the reference frames is not already in a cache, these reference frames are decompressed and the uncompressed data for the reference frames as used by the decoder is stored in the cache prior to the decompression of the B-frame or P-frame.

Claims

1. A process for supporting off-speed playback of video data encoded using long groups of pictures, comprising:

reading compressed data for a group of pictures containing the single frame into a buffer;

displaying a single frame from among frames in the group of pictures by;

maintaining most recently used decompressed reference frames in a cache;

decompressing compressed data from the buffer for at least one reference frame of the group of pictures used to decompress the single frame, if uncompressed data for the at least one reference frame is not in the cache;

providing the uncompressed data for at least one reference frame from the cache, the compressed data from the buffer for the single frame and state information to a stateless, single frame decoder; and

receiving from the single frame decoder the decompressed data for the single frame.

2. A motion video editing system, comprising:

storage for making available data files containing video data encoded using long groups of pictures;

an editing interface enabling a user to specify a sequence of clips of video data from the data files in the storage;

a streaming decoder having an input for receiving video data encoded using long groups of pictures and an output for providing a stream of decompressed data for a sequence of images from the received video data;

a stateless, single frame decoder, having inputs for receiving uncompressed data for at least one reference frame from video data encoded using long groups of pictures, compressed data for a single frame from the encoded video data and state information for decompressing the encoded video data and an output for providing decompressed data for the single image;

wherein, in response to a request through the editing interface for playback of a plurality of images at full frame rates, the streaming decoder is used to playback the plurality of images; and

wherein, in response to a request through the editing interface for playback of one or more images at an offspeed rate, the stateless, single frame decoder is used to playback each of the one or more images.

3. The motion video editing system of claim 2, wherein the video data encoded using long groups of pictures includes MPEG-2 data.

4. A single-frame stateless decoder for decoding one or more images from video data encoded using long groups of pictures for use in offspeed playback of the one or more images, comprising:

inputs for receiving uncompressed data for at least one reference frame from video data encoded using long groups of pictures, and compressed data for a single frame from the encoded video data and state information for decompressing the encoded video data; and

a decoder for generating decompressed data for the single image from the uncompressed data for the at least one reference frame, the compressed data for a single frame from the encoded video data and state information for decompressing the encoded video data.

5. The single-frame stateless decoder for claim 4, further comprising:

an input for receiving compressed data for a group of pictures containing the single frame from a compressed data buffer; and

an input for receiving uncompressed data for a reference frame from a cache.

6. The single-frame stateless decoder for claim 4, wherein the decoder further comprises:

means for decompressing compressed data from the buffer for reference frames of the group of pictures used to decompress the single frame, if the uncompressed data for reference frames are not in the cache, and for updating the cache to include the uncompressed data for the reference frames.