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
}