mirror of https://bitbucket.org/ausocean/av.git
81 lines
2.3 KiB
Go
81 lines
2.3 KiB
Go
/*
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DESCRIPTION
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extract.go provides an Extractor to get JPEG images from an RTP/JPEG stream
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defined by RFC 2435 (see https://tools.ietf.org/html/rfc2435).
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AUTHOR
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Saxon Nelson-Milton <saxon@ausocean.org>
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LICENSE
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Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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package mjpeg
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import (
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"fmt"
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"io"
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"time"
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"bitbucket.org/ausocean/av/protocol/rtp"
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)
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const maxRTPSize = 1500 // Max ethernet transmission unit in bytes.
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// Extractor is an Extractor for extracting JPEG from an RTP stream.
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type Extractor struct {
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dst io.Writer // The destination we'll be writing extracted JPEGs to.
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}
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// NewExtractor returns a new Extractor.
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func NewExtractor() *Extractor { return &Extractor{} }
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// Extract will continously read RTP packets from src containing JPEG (in RTP
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// payload format) and extract the JPEG images, sending them to dst. This
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// function expects that each read from src will provide a single RTP packet.
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func (e *Extractor) Extract(dst io.Writer, src io.Reader, delay time.Duration) error {
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buf := make([]byte, maxRTPSize)
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c := NewCtx(dst)
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for {
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n, err := src.Read(buf)
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switch err {
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case nil: // Do nothing.
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case io.EOF:
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return nil
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default:
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return fmt.Errorf("source read error: %v\n", err)
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}
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// Get payload from RTP packet.
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p, err := rtp.Payload(buf[:n])
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if err != nil {
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return fmt.Errorf("could not get RTP payload: %w\n", err)
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}
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// Also grab the marker so that we know when the JPEG is finished.
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m, err := rtp.Marker(buf[:n])
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if err != nil {
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return fmt.Errorf("could not read RTP marker: %w", err)
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}
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err = c.ParsePayload(p, m)
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if err != nil {
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return fmt.Errorf("could not parse JPEG scan: %w", err)
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}
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}
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}
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