FFMPEG (C++) convert & compress a single image out of buffer - c++

Question

i try to encode (with compression) and decode (without compression) a image with ffmpeg. But if i want to get the sent image back with avcodec_receive_packet i get only the error AVERROR(EAGAIN).
It doesnt matter what i change ... allways AVERROR(EAGAIN) is the outcome. Is it maybe a problem of sending just one single frame to the encoder? And if yes, how to fix it?
Code (only relevant stuff shown):
avcodec_register_all();
/* ------ init codec ------------------*/
AVCodec *codec;
codec = avcodec_find_decoder(AV_CODEC_ID_H264);
if (!codec)
{
print("compressH264, could not find decoder:\"AV_CODEC_ID_H264\"!!!");
return false;
}
AVCodec *nVidiaCodec = avcodec_find_encoder_by_name("h264_nvenc");
if (!nVidiaCodec)
{
print("err");
}
/* ------ ------------ ------------------*/
/* ------ init context ------------------*/
AVCodecContext* av_codec_context_ = NULL;
av_codec_context_ = avcodec_alloc_context3(nVidiaCodec);
if (!av_codec_context_)
{
print("compressH264, avcodec_alloc_context3 failed!!!");
return false;
}
int w = imgSrc.width();
int h = imgSrc.height();
if ((w % 2) != 0)
{
++w;
}
if ((h % 2) != 0)
{
++h;
}
av_codec_context_->width = w;
av_codec_context_->height = h;
av_codec_context_->pix_fmt = AV_PIX_FMT_YUV420P;
av_codec_context_->gop_size = 1;
av_codec_context_->max_b_frames = 1;
av_codec_context_->bit_rate = 400000;
av_codec_context_->time_base.den = 1;
av_codec_context_->time_base.num = 1;
av_opt_set(av_codec_context_->priv_data, "preset", "slow", 0);
int ret = avcodec_open2(av_codec_context_, nVidiaCodec, NULL);
if (0 > ret)
{
print("compressH264, could not open codec context for decoder:\"AV_CODEC_ID_H264\"!!!");
return false;
}
AVFrame *picture = av_frame_alloc();
picture->format = AV_PIX_FMT_RGB24;
picture->width = w;
picture->height = h;
ret = avpicture_fill((AVPicture *)picture, imgSrc.bits(), AV_PIX_FMT_RGB24, w, h);
if (0 > ret)
{
print("compressH264, avpicture_fill - failed!!!");
return false;
}
AVFrame *tmp_picture = av_frame_alloc();
tmp_picture->format = AV_PIX_FMT_YUV420P;
tmp_picture->width = w;
tmp_picture->height = h;
ret = av_frame_get_buffer(tmp_picture, 32);
SwsContext *img_convert_ctx = sws_getContext(av_codec_context_->width, av_codec_context_->height, AV_PIX_FMT_RGB24, av_codec_context_->width, av_codec_context_->height, av_codec_context_->pix_fmt, SWS_BICUBIC, NULL, NULL, NULL);
ret = sws_scale(img_convert_ctx, picture->data, picture->linesize, 0, av_codec_context_->height, tmp_picture->data, tmp_picture->linesize);
int h264Size = avpicture_get_size(AV_PIX_FMT_YUV420P, w, h);
ret = avcodec_send_frame(av_codec_context_, tmp_picture);
if (0 > ret)
{
char err[AV_ERROR_MAX_STRING_SIZE];
av_make_error_string(err, AV_ERROR_MAX_STRING_SIZE, ret);
print("compressH264, avcodec_send_frame: %s", err);
}
AVPacket *pkt = av_packet_alloc();
while (ret >= 0)
{
ret = avcodec_receive_packet(av_codec_context_, pkt);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
{
break;
}
else if (ret < 0)
{
fprintf(stderr, "Error during encoding\n");
exit(1);
}
av_packet_unref(pkt);
}
print("success");
Everything works well until:
- avcodec_receive_packet ... i get all time the error AVERROR(EAGAIN).
I can start decoding just if i have the compressed image.
Thanks for your help guys.
Edit:
If i do now the following code, i get a packet and ret == 0, but i have to send 46 times the same image ... for me this makes no sence.
do
{
ret = avcodec_receive_packet(av_codec_context_, &pkt);
if (ret == 0)
{
break;
}
else if ((ret < 0) && (ret != AVERROR(EAGAIN)))
{
coutF("error");
}
else if (ret == AVERROR(EAGAIN))
{
ret = avcodec_send_frame(av_codec_context_, tmp_picture);
if (0 > ret)
{
char err[AV_ERROR_MAX_STRING_SIZE];
av_make_error_string(err, AV_ERROR_MAX_STRING_SIZE, ret);
coutFRed("compressH264, avcodec_send_frame: %s", err);
}
coutF("cnt:%d", ++cnt);
}
} while (ret == 0);
Edit:
Good morning,
after more invest, i got the issue. I have to send the same frame a lot of time, because of the keyframe stuff for h264. The question now is, if it is possible to remove the h264 standart stuff from the encoder and just let FFMPEG convert one single frame.

Answer 1

I am not sure but following an ffmpeg example it seems that that just means it is done and you should return like they do in this code snippet:
/* if no more frames for output - returns AVERROR(EAGAIN)
* if flushed and no more frames for output - returns AVERROR_EOF
* rewrite retcode to 0 to show it as normal procedure completion
*/
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
ret = 0;
In their comments they seem to imply that it signals "normal procedure completion"

Answer 2

the answer for this issue is this:
do
{
ret = avcodec_receive_packet(av_codec_context_, &pkt);
if (ret == 0)
{
break;
}
else if ((ret < 0) && (ret != AVERROR(EAGAIN)))
{
return false;
}
else if (ret == AVERROR(EAGAIN))
{
ret = avcodec_send_frame(av_codec_context_, NULL);
if (0 > ret)
{
return false;
}
}
} while (ret == 0);
The NULL frame will flush the buffer and we are able to get the encoded frame.