MJPEGDecoder Class Reference

Motion-JPEG video decoder: wraps JPEGDecoder (https://github.com/Bodmer/JPEGDecoder) as a VideoDecoder, so it can be plugged directly into e.g. DemuxerAVI::setOutputVideo()/ DemuxerMP4::setOutputVideo() - the same role H264Decoder (CodecH264.h) and MPGDecoder (CodecMPG.h) play for their own codecs. Named "MJPEGDecoder" rather than reusing JPEGDecoder's own name to avoid shadowing that (global-namespace) class from within this one. More...

#include <CodecJPEG.h>

Inheritance diagram for MJPEGDecoder:

Public Member Functions
	MJPEGDecoder ()=default
	MJPEGDecoder (Print &out)
	MJPEGDecoder (VideoOutput &out)
bool	begin () override
	Initializes the decoder (allocates its picture buffers, etc).
void	end () override
	Releases the decoder's resources.
void	flush () override
void	setOutput (Print &out)
void	setOutput (VideoOutput &out)
void	setVideoFormat (VideoFormat format) override
VideoInfo	videoInfo () override
size_t	write (const uint8_t *data, size_t len) override

Protected Member Functions
void	decodeToFrameBuffer ()
size_t	writeToOutput (const uint8_t *data, size_t len)

Protected Attributes
Vector< uint8_t >	frame_buffer
uint16_t	height_ = 0
Vector< uint8_t >	img_vector
JPEGDecoder	jpeg_decoder
Print *	p_out = nullptr
VideoOutput *	p_out_video = nullptr
size_t	pos = 0
uint64_t	start_ms = 0
uint16_t	width_ = 0

Detailed Description

Motion-JPEG video decoder: wraps JPEGDecoder (https://github.com/Bodmer/JPEGDecoder) as a VideoDecoder, so it can be plugged directly into e.g. DemuxerAVI::setOutputVideo()/ DemuxerMP4::setOutputVideo() - the same role H264Decoder (CodecH264.h) and MPGDecoder (CodecMPG.h) play for their own codecs. Named "MJPEGDecoder" rather than reusing JPEGDecoder's own name to avoid shadowing that (global-namespace) class from within this one.

write()/flush() implement the VideoOutput contract (see Video.h), but unlike H264Decoder/MPGDecoder - which decode incrementally as Annex-B/ PES bytes arrive, with no separate "frame complete" signal needed - a bare JPEG byte stream has no equivalent self-framing a demuxer can use to decode early. write() therefore just accumulates one JPEG image's bytes, and flush() (called by e.g. DemuxerAVI/DemuxerMP4 at each frame boundary) decodes the assembled image directly into a full-frame RGB565 buffer and writes it to the target configured via setOutput(), one write() call per decoded picture - same convention as H264Decoder/ MPGDecoder, so any VideoOutput (OutputTFT_eSPI, OutputTinyGPU, OutputOpenCV, ...) works unchanged regardless of which codec produced the picture.

Author

Phil Schatzmann

Copyright

GPLv3

Constructor & Destructor Documentation

MJPEGDecoder() [1/3]

MJPEGDecoder ( )

default

MJPEGDecoder() [2/3]

MJPEGDecoder ( Print &  out )

inline

MJPEGDecoder() [3/3]

MJPEGDecoder ( VideoOutput &  out )

inline

Member Function Documentation

begin()

bool begin ( )

inlineoverridevirtual

Initializes the decoder (allocates its picture buffers, etc).

Implements VideoDecoder.

decodeToFrameBuffer()

void decodeToFrameBuffer ( )

inlineprotected

Reads every MCU block JPEGDecoder produces for the image just handed to decodeArray() and copies it into frame_buffer, row by row (source rows are MCUWidth pixels wide even for a right/bottom edge block narrower/shorter than that - only its top-left corner holds valid pixels - so a straight linear copy would misalign those edge blocks).

end()

void end ( )

inlineoverridevirtual

Releases the decoder's resources.

Implements VideoDecoder.

flush()

void flush ( )

inlineoverridevirtual

Decodes the assembled JPEG image and writes the resulting RGB565 frame to setOutput()'s target, then resets for the next frame - a no-op if write() hasn't accumulated anything since the last call.

Reimplemented from VideoOutput.

setOutput() [1/2]

void setOutput ( Print &  out )

inlinevirtual

Defines the target the decoded picture is written to, one write() call per decoded picture (RGB565 - the only format JPEGDecoder produces).

Implements VideoDecoder.

setOutput() [2/2]

void setOutput ( VideoOutput &  out )

inline

setVideoFormat()

void setVideoFormat ( VideoFormat  format )

inlineoverridevirtual

JPEGDecoder only ever produces RGB565 - any other value is logged and ignored.

Implements VideoDecoder.

videoInfo()

VideoInfo videoInfo ( )

inlineoverridevirtual

Reports the dimensions of the most recently decoded picture - 0 before any picture has been decoded.

Implements VideoDecoder.

write()

size_t write ( const uint8_t *  data, size_t  len  )

inlineoverridevirtual

Accumulates one JPEG image's bytes - may be called more than once per frame (e.g. from a demuxer that hands over payload in pieces). Decoding happens on flush(), not here.

Implements VideoOutput.

writeToOutput()

size_t writeToOutput ( const uint8_t *  data, size_t  len  )

inlineprotected

Member Data Documentation

frame_buffer

Vector<uint8_t> frame_buffer

protected

height_

uint16_t height_ = 0

protected

img_vector

Vector<uint8_t> img_vector

protected

jpeg_decoder

JPEGDecoder jpeg_decoder

protected

p_out

Print* p_out = nullptr

protected

p_out_video

VideoOutput* p_out_video = nullptr

protected

pos

size_t pos = 0

protected

start_ms

uint64_t start_ms = 0

protected

width_

uint16_t width_ = 0

protected

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The documentation for this class was generated from the following file:

• src/AudioTools/Video/CodecJPEG.h