AVFormatContext *oc;

AVPicture spicture,
          dpicture;

enum AVPixelFormat sfmt = PIX_FMT_RGB32;

int iwidth = 1280;
int iheight = 360;

avformat_alloc_output_context2(&oc, NULL, "flv", fname);
avio_open(&oc->pb, URLBytes, AVIO_FLAG_WRITE);

AVCodec cvideo = avcodec_find_encoder(AV_CODEC_ID_H264);
AVStream svideo = avformat_new_stream(oc, cvideo);

svideo->codec->pix_fmt       = PIX_FMT_YUV420P;
svideo->codec->bit_rate      = 921000;
svideo->codec->width         = iwidth / 2;
svideo->codec->height        = iheight;
svideo->codec->time_base.num = 1;
svideo->codec->time_base.den = FLV_TIMEBASE;
svideo->codec->codec_tag     = FLV_TAG_TYPE_VIDEO;
svideo->codec->flags        |= CODEC_FLAG_GLOBAL_HEADER;

avcodec_open2(svideo->codec, cvideo, NULL);

avpicture_alloc(&spicture, sfmt, iwidth, iheight);
avpicture_alloc(&dpicture, svideo->codec->pix_fmt, iwidth, iheight * 2);

AVFrame *frame = avcodec_alloc_frame();

*((AVPicture *) frame) = dpicture;

// ...
// fill and scale dpicture

int w, h;
unsigned char *buffer = extractPixelBuffer(sampleBuffer, &w, &h);

avpicture_fill(&spicture, buffer, sfmt, w, h);

SwsContext *swsCtx = sws_getContext(w, h, sfmt,
                                    iwidth,
                                    iheight * 2,
                                    svideo->codec->pix_fmt,
                                    SWS_BICUBIC, NULL, NULL, NULL);

sws_scale(swsCtx,
          (const uint8_t * const *) spicture.data,
          spicture.linesize,
          0, iheight,
          dpicture.data,
          dpicture.linesize);

sws_freeContext(swsCtx);

// ...
// encode frame and write it to video

int succ, ret;

AVPacket pkt = {0};
av_init_packet(&pkt);

avcodec_encode_video2(svideo->codec, &pkt, frame, &succ);
av_interleaved_write_frame(oc, &pkt);