static int pcx_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
                            AVPacket *avpkt) {
    const uint8_t *buf = avpkt->data;
    int buf_size = avpkt->size;
    PCXContext * const s = avctx->priv_data;
    AVFrame *picture = data;
    AVFrame * const p = &s->picture;
    int compressed, xmin, ymin, xmax, ymax;
    unsigned int w, h, bits_per_pixel, bytes_per_line, nplanes, stride, y, x,
                 bytes_per_scanline;
    uint8_t *ptr;
    uint8_t const *bufstart = buf;
    uint8_t *scanline;
    int ret = -1;

    if (buf[0] != 0x0a || buf[1] > 5) {
        av_log(avctx, AV_LOG_ERROR, "this is not PCX encoded data\n");
        return AVERROR_INVALIDDATA;
    }

    compressed = buf[2];
    xmin = AV_RL16(buf+ 4);
    ymin = AV_RL16(buf+ 6);
    xmax = AV_RL16(buf+ 8);
    ymax = AV_RL16(buf+10);

    if (xmax < xmin || ymax < ymin) {
        av_log(avctx, AV_LOG_ERROR, "invalid image dimensions\n");
        return AVERROR_INVALIDDATA;
    }

    w = xmax - xmin + 1;
    h = ymax - ymin + 1;

    bits_per_pixel     = buf[3];
    bytes_per_line     = AV_RL16(buf+66);
    nplanes            = buf[65];
    bytes_per_scanline = nplanes * bytes_per_line;

    if (bytes_per_scanline < w * bits_per_pixel * nplanes / 8) {
        av_log(avctx, AV_LOG_ERROR, "PCX data is corrupted\n");
        return AVERROR_INVALIDDATA;
    }

    switch ((nplanes<<8) + bits_per_pixel) {
        case 0x0308:
            avctx->pix_fmt = AV_PIX_FMT_RGB24;
            break;
        case 0x0108:
        case 0x0104:
        case 0x0102:
        case 0x0101:
        case 0x0401:
        case 0x0301:
        case 0x0201:
            avctx->pix_fmt = AV_PIX_FMT_PAL8;
            break;
        default:
            av_log(avctx, AV_LOG_ERROR, "invalid PCX file\n");
            return AVERROR_INVALIDDATA;
    }

    buf += 128;

    if (p->data[0])
        avctx->release_buffer(avctx, p);

    if (av_image_check_size(w, h, 0, avctx))
        return AVERROR_INVALIDDATA;
    if (w != avctx->width || h != avctx->height)
        avcodec_set_dimensions(avctx, w, h);
    if ((ret = avctx->get_buffer(avctx, p)) < 0) {
        av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
        return ret;
    }

    p->pict_type = AV_PICTURE_TYPE_I;

    ptr    = p->data[0];
    stride = p->linesize[0];

    scanline = av_malloc(bytes_per_scanline);
    if (!scanline)
        return AVERROR(ENOMEM);

    if (nplanes == 3 && bits_per_pixel == 8) {
        for (y=0; y<h; y++) {
            buf = pcx_rle_decode(buf, scanline, bytes_per_scanline, compressed);

            for (x=0; x<w; x++) {
                ptr[3*x  ] = scanline[x                    ];
                ptr[3*x+1] = scanline[x+ bytes_per_line    ];
                ptr[3*x+2] = scanline[x+(bytes_per_line<<1)];
            }

            ptr += stride;
        }

    } else if (nplanes == 1 && bits_per_pixel == 8) {
        const uint8_t *palstart = bufstart + buf_size - 769;

        for (y=0; y<h; y++, ptr+=stride) {
            buf = pcx_rle_decode(buf, scanline, bytes_per_scanline, compressed);
            memcpy(ptr, scanline, w);
        }

        if (buf != palstart) {
            av_log(avctx, AV_LOG_WARNING, "image data possibly corrupted\n");
            buf = palstart;
        }
        if (*buf++ != 12) {
            av_log(avctx, AV_LOG_ERROR, "expected palette after image data\n");
            ret = AVERROR_INVALIDDATA;
            goto end;
        }

    } else if (nplanes == 1) {   /* all packed formats, max. 16 colors */
        GetBitContext s;

        for (y=0; y<h; y++) {
            init_get_bits(&s, scanline, bytes_per_scanline<<3);

            buf = pcx_rle_decode(buf, scanline, bytes_per_scanline, compressed);

            for (x=0; x<w; x++)
                ptr[x] = get_bits(&s, bits_per_pixel);
            ptr += stride;
        }

    } else {    /* planar, 4, 8 or 16 colors */
        int i;

        for (y=0; y<h; y++) {
            buf = pcx_rle_decode(buf, scanline, bytes_per_scanline, compressed);

            for (x=0; x<w; x++) {
                int m = 0x80 >> (x&7), v = 0;
                for (i=nplanes - 1; i>=0; i--) {
                    v <<= 1;
                    v  += !!(scanline[i*bytes_per_line + (x>>3)] & m);
                }
                ptr[x] = v;
            }
            ptr += stride;
        }
    }

    if (nplanes == 1 && bits_per_pixel == 8) {
        pcx_palette(&buf, (uint32_t *) p->data[1], 256);
    } else if (bits_per_pixel * nplanes == 1) {
        AV_WN32A(p->data[1]  , 0xFF000000);
        AV_WN32A(p->data[1]+4, 0xFFFFFFFF);
    } else if (bits_per_pixel < 8) {
        const uint8_t *palette = bufstart+16;
        pcx_palette(&palette, (uint32_t *) p->data[1], 16);
    }

    *picture = s->picture;
    *data_size = sizeof(AVFrame);

    ret = buf - bufstart;
end:
    av_free(scanline);
    return ret;
}