// buffer allocation code omitted

codec = avcodec_find_encoder(CODEC_ID_MSMPEG4V1);

if (!codec)
{
    NSLog("Couldn't init codec");
    abort();
}

codecContext = avcodec_alloc_context();
codecContext->bit_rate = 384000;
codecContext->width = FRAME_WIDTH;
codecContext->height = FRAME_HEIGHT;
codecContext->time_base = (AVRational) {
    1,
    FPS
};

codecContext->pix_fmt = PIX_FMT_YUV420P;

int codec_open_result = avcodec_open(codecContext, codec);

if (codec_open_result < 0)
{
    NSLog(@"Couldn't open codec");
    abort();
}

/* previously defined
#define FRAME_WIDTH  320
#define FRAME_HEIGHT 480
*/

uint8_t *rgb_data = buffer + (frameSize * ((*totalCaptured - 1) % BUFFER_FRAME_MAX_COUNT));

uint8_t *rgb_src[3] = {
    rgb_data,
    NULL,
    NULL
};

int rgb_stride[3] = {
    4 * FRAME_WIDTH,
    0,
    0
};

uint8_t *src[4] = {
    scaleBuffer,
    scaleBuffer + FRAME_WIDTH * FRAME_HEIGHT,
    scaleBuffer + ( FRAME_WIDTH * FRAME_HEIGHT ) + ( FRAME_WIDTH * FRAME_HEIGHT / 4 ),
    NULL
};

int stride[4] = {
    FRAME_WIDTH,
    FRAME_WIDTH / 2,
    FRAME_WIDTH / 2,
    0
};

struct SwsContext *sws;

sws = sws_getContext(FRAME_WIDTH,       // src width
                     FRAME_HEIGHT,      // src height
                     PIX_FMT_RGB32,     // src pixel format ,
                     FRAME_WIDTH,       // dest width
                     FRAME_HEIGHT,      // dest height
                     PIX_FMT_YUV420P,   // dest pix format
                     SWS_BILINEAR,      // FLAGS
                     NULL,
                     NULL,
                     NULL);


int sliceHeight = sws_scale(sws,
                            rgb_src,
                            rgb_stride,
                            0,
                            FRAME_HEIGHT,
                            src,
                            stride);

// the "sliceHeight" variable evaluates to 480 in GDB at this point, which seems correct

if (sliceHeight <= 0)
{
    NSLog(@"couldn't scale");
    abort();
}

sws_freeContext(sws);

currentPicture->data[0] = src[0];
currentPicture->data[1] = src[1];
currentPicture->data[2] = src[2];
currentPicture->data[3] = src[3];

currentPicture->linesize[0] = stride[0];
currentPicture->linesize[1] = stride[1];
currentPicture->linesize[2] = stride[2];
currentPicture->linesize[3] = stride[3];

int out_size = avcodec_encode_video(codecContext, encodeBuffer, frameSize, currentPicture);

// the "out_size" variable evaluates to 4 in GDB, which seems incorrect