Exemple #1
0
func Rescale(a, b, c int64) int64 {
	return int64(C.av_rescale(C.int64_t(a), C.int64_t(b), C.int64_t(c)))
}
// ImageWxH returns a screenshot at the ts milliseconds, scaled to the specified width and height.
func (g *Generator) ImageWxH(ts int64, width, height int) (image.Image, error) {
	img := image.NewRGBA(image.Rect(0, 0, width, height))
	frame := C.av_frame_alloc()
	defer C.av_frame_free(&frame)
	frameNum := C.av_rescale(
		C.int64_t(ts),
		C.int64_t(g.streams[g.vStreamIndex].time_base.den),
		C.int64_t(g.streams[g.vStreamIndex].time_base.num),
	) / 1000
	if C.avformat_seek_file(
		g.avfContext,
		C.int(g.vStreamIndex),
		0,
		frameNum,
		frameNum,
		C.AVSEEK_FLAG_FRAME,
	) < 0 {
		return nil, errors.New("can't seek to timestamp")
	}
	C.avcodec_flush_buffers(g.avcContext)
	var pkt C.struct_AVPacket
	var frameFinished C.int
	for C.av_read_frame(g.avfContext, &pkt) == 0 {
		if int(pkt.stream_index) != g.vStreamIndex {
			C.av_free_packet(&pkt)
			continue
		}
		if C.avcodec_decode_video2(g.avcContext, frame, &frameFinished, &pkt) <= 0 {
			C.av_free_packet(&pkt)
			return nil, errors.New("can't decode frame")
		}
		C.av_free_packet(&pkt)
		if frameFinished == 0 || pkt.dts < frameNum {
			continue
		}
		ctx := C.sws_getContext(
			C.int(g.Width),
			C.int(g.Height),
			g.avcContext.pix_fmt,
			C.int(width),
			C.int(height),
			C.PIX_FMT_RGBA,
			C.SWS_BICUBIC,
			nil,
			nil,
			nil,
		)
		if ctx == nil {
			return nil, errors.New("can't allocate scaling context")
		}
		srcSlice := (**C.uint8_t)(&frame.data[0])
		srcStride := (*C.int)(&frame.linesize[0])
		dst := (**C.uint8_t)(unsafe.Pointer(&img.Pix))
		dstStride := (*C.int)(unsafe.Pointer(&[1]int{img.Stride}))
		C.sws_scale(
			ctx,
			srcSlice,
			srcStride,
			0,
			g.avcContext.height,
			dst,
			dstStride,
		)
		break
	}
	return img, nil
}