Video Processing Dinesh Ganotra. Terminologies Frames = Images frame size : WxH Color depth : Pixel...
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Transcript of Video Processing Dinesh Ganotra. Terminologies Frames = Images frame size : WxH Color depth : Pixel...
Terminologies
• Frames = Images• frame size : WxH• Color depth : Pixel represented by fixed amount of bits• Duration: T• FPS: Frames per Second• Pixel per frame: WxHxCD• Bits per frame: • Bit rate:• Video Size:• Low Level profile: Minimum video specification that any video
decoder should be able to handle
Peak Signal-to-Noise Ratio (PSNR), a metric for the "quality" of compressed video images, while the horizontal axis shows the transmission bit rate.10 frames per second, 176x144 (QCIF) resolution, 10 seconds of video, (100 frames)
Microsoft
• AVI : Audio/Video Interleaved File Format• ( Video for Windows: 1992)• Do not have pixel aspect ratio information
Hdrl tagWidth , height , frame rate
movi tagAudio , video data
Idex1 tagIndexing info
Apple
• MOV: Quicktime File FormatContainer file that contains one or more
tracks, each of which stores a particular type of data: audio, video, effects, or text (e.g. for subtitles).– Can also be data reference to the media stream
located in another file– Suited for editing.
MPEG-1
• color-space is transformed to YCbCr• Chroma is also sub-sampled to 4:2:0, meaning it is
reduced by one half vertically and one half horizontally
• Because of sub-sampling, YCbCr video must always be stored using even dimensions (divisible by 2), otherwise chroma mismatch ("ghosts") will occur, and it will appear as if the color is ahead of, or behind the rest of the video, much like a shadow.
Frame Types• Intra-frames: can be decoded independently of any other frame.
Effectively identical to baseline JPEG. • GOP: group of pictures: typically 17-18 non I-frames are their
between two I –frames• Predicted-frames: improve compression by exploiting the temporal
(over time) redundancy in a video. P-frames store only the difference in image from the frame (either an I-frame or P-frame) immediately preceding it.
• Bidirectional Frames: Can make prediction using both previous and future frames. Often avoided, not fully supported by hardware.
• D-frame: only DC component is encoded. Poor quality images, only used to find frames in videos. Obsolete.
MacroBlocks
• 8x8 blocks for quantization. However, because chroma (color) is subsampled by a factor of 4, each pair of (red and blue) chroma blocks corresponds to 4 different luma blocks. This set of 6 blocks, with a resolution of 16x16, is called a macroblock.
Motion Vector
The encoder compares the current frame with adjacent parts of the video from the anchor frame (previous I- or P- frame) in a diamond pattern, up to a (encoder-specific) predefined radius limit from the area of the current macroblock. If a match is found, only the direction and distance (i.e. the vector of the motion) from the previous video area to the current macroblock need to be encoded into the inter-frame (P- or B- frame).
DIVX
• Digital Video Express• Interactive video menus • Multiple subtitles (XSUB) • Multiple audio tracks
FLV
• Flash Live Video• Originally developed by Macromedia , now
maintained by Adobe Systems• Contain material encoded with codecs
following the Sorenson Spark or VP6 video compression formats, protected by patents
Year Wise Progress• Year Standard Application• 1984 H.120 • 1990 H.261 Videoconferencing, Videotelephony • 1993 MPEG-1 ISO, IEC Video-CD • 1995 H.262/MPEG-2 DVD Video , Blu-Ray , Digital
Video Broadcasting, SVCD • 1996 H.263 T Videoconferencing, Videotelephony,
Video on Mobile Phones (3GP) • 1999 MPEG-4 Video on Internet (DivX, Xvid
...) • 2003 H.264/MPEG-4 Blu-Ray , Digital Video Broadcasting,
iPod Video , HD DVD
Video Codecs are generally installed in the windows installation
mrle Microsoft Run Length Encoding (msrle32.dll) msvc Microsoft Video 1 (msvidc32.dll) i420 Intel Indeo 4 codec (iyuv_32.dll) cvid Supermac Cinepak (iccvid.dll)
8,8 ,16 ,16
• All the video compression algorithms work on the DCT 8 cross 8 pixel blocks and macro-blocks are 16 cross 16 pixels block. So, its advisable to work with frames whose sizes are multiples of 16 and avoid exception handling algorithms and unnecessarily slowing down the compression/decompression algorithms.
Support for B-frames
Variable bit rate audio Variable frame rate Captions (Subtitles)
Video formats supported
Audio formats supported
Metadata/Tags supported Menu Support
3GP Yes Yes Yes 3GPP Timed Text
H.263, MPEG-4 Part 2 and H.264/MPEG-4 AVC
AMR-NB, AMR-WB, AMR-WB+, AAC, HE-AAC and HE-AAC v2 ? No
FLV Yes ? Yes No
Sorenson, VP6, Screen Video, H.264/MPEG-4 AVC
MP3, Nellymoser, ADPCM, Linear PCM, AAC[9], Speex[10] Yes No
mov Yes Yes Yes Yes
Limited to what is available to the QuickTime codec manager
Limited to what is available to Sound Manager or CoreAudio Yes
Can be done by using sprite tracks
divx Yes Yes Yes Yes
MPEG-4 Part 2 video encoded to meet DivX profiles MP3, PCM, AC-3 ? Yes
wmv Yes Yes Yes Yes
Almost anything through VFW or DMO; H.264/AVC is problematic
Almost anything through ACM or DMO; Vorbis is problematic Yes ?
AVI Yes Yes Yes Yes
Almost anything through VFW; H.264/AVC is problematic due to the limited B-frame support
Almost anything through ACM; Vorbis is problematic [5] not officially No
mpeg Yes Yes Yes No MPEG-1, MPEG-2
MPEG-1 Layers I, II, III (mp3), other formats only in private streams: LPCM[15] No No
Algorithm for m2v format
• BitStream [];• BitStream = Alignbits(BitStream)• BitStream = PutSequenceHeader(BitStream)• BitStream = Alignbits(BitStream)• BitStream = PutSequenceExtension(BitStream)• BitStream = Alignbits(BitStream)• BitStream = PutSequenceDisplayExtension(BitStream)• BitStream = Alignbits(BitStream)• BitStream = PutGOPHeader(BitStream)
• frame_Y_trfmd(row:row+7,col:col+7) = floor(dct2(frame_Y(row:row+7, col:col+7)) + 0.5);
• BitStream = PutPictureHeader(BitStream);• BitStream = Alignbits(BitStream);• BitStream = PutPictureCodingExtn(BitStream);• frame_Y_trfmd_Quant(row:row+7,col:col+7) =
round((frame_Y_trfmd(row:row+7,col:col+7)./(intra_quant_mat.*QUANT)).*tempmat);
• BitStream = Alignbits(BitStream);• BitStream = PutSliceHeader(ind_slice, BitStream); % Each row
is a slice•