smc.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

                        pixels[block_ptr++] = pixel;
                    }
                    block_ptr += row_inc;
                }
                ADVANCE_BLOCK();
            }
            break;

        /* 2-color block encoding */
        case 0x80:
        case 0x90:
            n_blocks = (opcode & 0x0F) + 1;

            /* figure out which color pair to use to paint the 2-color block */
            if ((opcode & 0xF0) == 0x80) {
                /* fetch the next 2 colors from bytestream and store in next
                 * available entry in the color pair table */
                for (i = 0; i < CPAIR; i++) {
                    pixel = s->buf[stream_ptr++];
                    color_table_index = CPAIR * color_pair_index + i;
                    s->color_pairs[color_table_index] = pixel;
                }
                /* this is the base index to use for this block */
                color_table_index = CPAIR * color_pair_index;
                color_pair_index++;
                /* wraparound */
                if (color_pair_index == COLORS_PER_TABLE)
                    color_pair_index = 0;
            } else
                color_table_index = CPAIR * s->buf[stream_ptr++];

            while (n_blocks--) {
                color_flags = AV_RB16(&s->buf[stream_ptr]);
                stream_ptr += 2;
                flag_mask = 0x8000;
                block_ptr = row_ptr + pixel_ptr;
                for (pixel_y = 0; pixel_y < 4; pixel_y++) {
                    for (pixel_x = 0; pixel_x < 4; pixel_x++) {
                        if (color_flags & flag_mask)
                            pixel = color_table_index + 1;
                        else
                            pixel = color_table_index;
                        flag_mask >>= 1;
                        pixels[block_ptr++] = s->color_pairs[pixel];
                    }
                    block_ptr += row_inc;
                }
                ADVANCE_BLOCK();
            }
            break;

        /* 4-color block encoding */
        case 0xA0:
        case 0xB0:
            n_blocks = (opcode & 0x0F) + 1;

            /* figure out which color quad to use to paint the 4-color block */
            if ((opcode & 0xF0) == 0xA0) {
                /* fetch the next 4 colors from bytestream and store in next
                 * available entry in the color quad table */
                for (i = 0; i < CQUAD; i++) {
                    pixel = s->buf[stream_ptr++];
                    color_table_index = CQUAD * color_quad_index + i;
                    s->color_quads[color_table_index] = pixel;
                }
                /* this is the base index to use for this block */
                color_table_index = CQUAD * color_quad_index;
                color_quad_index++;
                /* wraparound */
                if (color_quad_index == COLORS_PER_TABLE)
                    color_quad_index = 0;
            } else
                color_table_index = CQUAD * s->buf[stream_ptr++];

            while (n_blocks--) {
                color_flags = AV_RB32(&s->buf[stream_ptr]);
                stream_ptr += 4;
                /* flag mask actually acts as a bit shift count here */
                flag_mask = 30;
                block_ptr = row_ptr + pixel_ptr;
                for (pixel_y = 0; pixel_y < 4; pixel_y++) {
                    for (pixel_x = 0; pixel_x < 4; pixel_x++) {
                        pixel = color_table_index +
                            ((color_flags >> flag_mask) & 0x03);
                        flag_mask -= 2;
                        pixels[block_ptr++] = s->color_quads[pixel];
                    }
                    block_ptr += row_inc;
                }
                ADVANCE_BLOCK();
            }
            break;

        /* 8-color block encoding */
        case 0xC0:
        case 0xD0:
            n_blocks = (opcode & 0x0F) + 1;

            /* figure out which color octet to use to paint the 8-color block */
            if ((opcode & 0xF0) == 0xC0) {
                /* fetch the next 8 colors from bytestream and store in next
                 * available entry in the color octet table */
                for (i = 0; i < COCTET; i++) {
                    pixel = s->buf[stream_ptr++];
                    color_table_index = COCTET * color_octet_index + i;
                    s->color_octets[color_table_index] = pixel;
                }
                /* this is the base index to use for this block */
                color_table_index = COCTET * color_octet_index;
                color_octet_index++;
                /* wraparound */
                if (color_octet_index == COLORS_PER_TABLE)
                    color_octet_index = 0;
            } else
                color_table_index = COCTET * s->buf[stream_ptr++];

            while (n_blocks--) {
                /*
                  For this input of 6 hex bytes:
                    01 23 45 67 89 AB
                  Mangle it to this output:
                    flags_a = xx012456, flags_b = xx89A37B
                */
                /* build the color flags */
                color_flags_a = color_flags_b = 0;
                color_flags_a =
                    (s->buf[stream_ptr + 0] << 16) |
                    ((s->buf[stream_ptr + 1] & 0xF0) << 8) |
                    ((s->buf[stream_ptr + 2] & 0xF0) << 4) |
                    ((s->buf[stream_ptr + 2] & 0x0F) << 4) |
                    ((s->buf[stream_ptr + 3] & 0xF0) >> 4);
                color_flags_b =
                    (s->buf[stream_ptr + 4] << 16) |
                    ((s->buf[stream_ptr + 5] & 0xF0) << 8) |
                    ((s->buf[stream_ptr + 1] & 0x0F) << 8) |
                    ((s->buf[stream_ptr + 3] & 0x0F) << 4) |
                    (s->buf[stream_ptr + 5] & 0x0F);
                stream_ptr += 6;

                color_flags = color_flags_a;
                /* flag mask actually acts as a bit shift count here */
                flag_mask = 21;
                block_ptr = row_ptr + pixel_ptr;
                for (pixel_y = 0; pixel_y < 4; pixel_y++) {
                    /* reload flags at third row (iteration pixel_y == 2) */
                    if (pixel_y == 2) {
                        color_flags = color_flags_b;
                        flag_mask = 21;
                    }
                    for (pixel_x = 0; pixel_x < 4; pixel_x++) {
                        pixel = color_table_index +
                            ((color_flags >> flag_mask) & 0x07);
                        flag_mask -= 3;
                        pixels[block_ptr++] = s->color_octets[pixel];
                    }
                    block_ptr += row_inc;
                }
                ADVANCE_BLOCK();
            }
            break;

        /* 16-color block encoding (every pixel is a different color) */
        case 0xE0:
            n_blocks = (opcode & 0x0F) + 1;

            while (n_blocks--) {
                block_ptr = row_ptr + pixel_ptr;
                for (pixel_y = 0; pixel_y < 4; pixel_y++) {
                    for (pixel_x = 0; pixel_x < 4; pixel_x++) {
                        pixels[block_ptr++] = s->buf[stream_ptr++];
                    }
                    block_ptr += row_inc;
                }
                ADVANCE_BLOCK();
            }
            break;

        case 0xF0:
            av_log(s->avctx, AV_LOG_INFO, "0xF0 opcode seen in SMC chunk (contact the developers)\n");
            break;
        }
    }
}

static int smc_decode_init(AVCodecContext *avctx)
{
    SmcContext *s = avctx->priv_data;

    s->avctx = avctx;
    avctx->pix_fmt = PIX_FMT_PAL8;
    dsputil_init(&s->dsp, avctx);

    s->frame.data[0] = NULL;

    return 0;
}

static int smc_decode_frame(AVCodecContext *avctx,
                             void *data, int *data_size,
                             uint8_t *buf, int buf_size)
{
    SmcContext *s = avctx->priv_data;

    s->buf = buf;
    s->size = buf_size;

    s->frame.reference = 1;
    s->frame.buffer_hints = FF_BUFFER_HINTS_VALID | FF_BUFFER_HINTS_PRESERVE |
                            FF_BUFFER_HINTS_REUSABLE | FF_BUFFER_HINTS_READABLE;
    if (avctx->reget_buffer(avctx, &s->frame)) {
        av_log(s->avctx, AV_LOG_ERROR, "reget_buffer() failed\n");
        return -1;
    }

    smc_decode_stream(s);

    *data_size = sizeof(AVFrame);
    *(AVFrame*)data = s->frame;

    /* always report that the buffer was completely consumed */
    return buf_size;
}

static int smc_decode_end(AVCodecContext *avctx)
{
    SmcContext *s = avctx->priv_data;

    if (s->frame.data[0])
        avctx->release_buffer(avctx, &s->frame);

    return 0;
}

AVCodec smc_decoder = {
    "smc",
    CODEC_TYPE_VIDEO,
    CODEC_ID_SMC,
    sizeof(SmcContext),
    smc_decode_init,
    NULL,
    smc_decode_end,
    smc_decode_frame,
    CODEC_CAP_DR1,
};