Error in avcodec_receive_packet (gdi screenshot + ffmpeg) - c++

Question

I try to capture windows screen with ffmpeg.
All's working, but avcodec_receive_packet return error AVERROR(EAGAIN)
and I can't undestand why it's happenning.
Can anybody give advice?
SwsContext* convertContext = sws_getContext(c->width, c->height, AV_PIX_FMT_BGRA, c->width, c->height, c->pix_fmt, SWS_FAST_BILINEAR, NULL, NULL, NULL);
for (int i = 0; i < fps*seconds; i++)
{
fflush(stdout);
/* make sure the frame data is writable */
ret = av_frame_make_writable(frame);
if (ret < 0)
exit(1);
gdi->MakeScreenshoot();
OutFrame->pts = i;
int ret = av_image_fill_arrays(GDIFrame->data, GDIFrame->linesize, gdi->m_bufferGDIBits, AV_PIX_FMT_BGRA, c->width, c->height, 1);
ret = av_image_fill_arrays(OutFrame->data, OutFrame->linesize, outbuffer, c->pix_fmt, c->width, c->height, 1);
GDIFrame->data[0] += GDIFrame->linesize[0] * (c->height - 1); // flipping frame
GDIFrame->linesize[0] *= -1;
int hslice = sws_scale(convertContext, GDIFrame->data, GDIFrame->linesize, 0, c->height,OutFrame->data, OutFrame->linesize);
/* encode the image */
encode(c, OutFrame, pkt, f);
}
static void encode(AVCodecContext *enc_ctx, AVFrame *frame, AVPacket *pkt, FILE *outfile)
{
int ret = -1;
/* send the frame to the encoder */
/*if (frame)
printf("Send frame %3"PRId64"\n", frame->pts);*/
ret = avcodec_send_frame(enc_ctx, frame);
if (ret < 0)
{
fprintf(stderr, "Error sending a frame for encoding\n");
exit(1);
}
while (ret >= 0)
{
ret = avcodec_receive_packet(enc_ctx, pkt);
if (ret == AVERROR_EOF)
return;
if (ret == AVERROR(EAGAIN))
return;
else
if (ret < 0)
{
fprintf(stderr, "Error during encoding\n");
exit(1);
}
//printf("Write packet %3"PRId64" (size=%5d)\n", pkt->pts, pkt->size);
fwrite(pkt->data, 1, pkt->size, outfile);
av_packet_unref(pkt);
}
}
If I comment
if (ret == AVERROR_EOF)
return;
if (ret == AVERROR(EAGAIN))
return;
else
if (ret < 0)
{
fprintf(stderr, "Error during encoding\n");
exit(1);
}
in encode function - all is fine, file will be written and will be correct, but I want solve the problem.

Answer 1

Bit late to the party.
I am also trying this out with encode_video.c
Seems that avcodec_receive_packet() will return these "errors" when encoder does not have a complete packet ready... possibly next call to avcodec_send_frame() will result in a full packet.
So just keep going.
The final call to avcodec_send_frame() with NULL frame will flush the final packet.