mp4dbuff.c

Intel提供的在Sitsang等嵌入式开发平台上使用Linux操作系统

/******************************************************************************
//               INTEL CORPORATION PROPRIETARY INFORMATION
//  This software is supplied under the terms of a license agreement or
//  nondisclosure agreement with Intel Corporation and may not be copied
//  or disclosed except in accordance with the terms of that agreement.
//        Copyright (c) 2003 Intel Corporation. All Rights Reserved.
//
//  Description:    Stream buffer processing functions of MPEG-4 video decoder
//                  sample code for Intel(R) Integrated Performance Primitives.
//  Functions List:
//		get_bits_mpeg4()
//      load_video_buffer()
//		rewind_buffer_mpeg4()
//      init_input_video_buffer()
//		release_input_video_buffer()
******************************************************************************/

#include <stdlib.h>
#include <memory.h>
#include "sampmp4.h"

/******************************************************************************
// Name:            rewind_buffer_mpeg4
// Description:     Skip N bits back in video buffer
// Input Arguments: 
//      stream_buf          - Pointer to the source compressed video bitstream
//      n_bits              - Number of bits to skip back
//
//  Output Arguments:
//      stream_buf          - Pointer to the updated source video stream after
//                            the N bits is skipped back
//
//  Returns:    
//      None
******************************************************************************/
void rewind_buffer_mpeg4 (sample_bitstream *stream_buf, int n_bits)
{
    int n_bytes;
    
    n_bytes  = (n_bits  >> 3);
    n_bits  -= (n_bytes << 3);

    if (stream_buf->bs_cur_bitoffset < n_bits) {
        stream_buf->bs_cur_byte -= 1;
        stream_buf->bs_cur_bitoffset += 8;
    }
    stream_buf->bs_cur_byte    -= n_bytes;
    stream_buf->bs_cur_bitoffset -= n_bits;
}
/******************************************************************************
// Name:                get_bits_mpeg4
// Description:         Read N bits from video buffer
// Input Arguments: 
//      stream_buf      - Pointer to the source compressed video bitstream
//      n_bits          - Number of bits to read, i.e., N. (N <= 32)
//
//  Output Arguments:
//      stream_buf      - Pointer to the updated source video stream after
//                        the N bits is taken out
//
//  Returns:    
//      the value of the N bits in big endian
******************************************************************************/
Ipp32u  get_bits_mpeg4 (sample_bitstream *stream_buf, int n_bits)
{
    Ipp32u  code = 0;
    int     n_head_bits, n_tail_bits, n_bytes;

    n_head_bits = stream_buf->bs_cur_bitoffset;
    
    n_bytes   = (n_head_bits + n_bits + 7) / 8;

    n_tail_bits = n_bytes * 8 - n_head_bits - n_bits;
    
    while (n_bytes--) {
        code = (code << 8) | (*(stream_buf->bs_cur_byte)++);
    }

    code = (code >> n_tail_bits) & bits_mask_tbl[n_bits];   

    if (n_tail_bits) {
        stream_buf->bs_cur_byte--;
        stream_buf->bs_cur_bitoffset = 8 - n_tail_bits;
    }
    else {
        stream_buf->bs_cur_bitoffset = 0;
    }

    return code;
}

/***************************************************************************
// Name:                    release_input_video_buffer
// Description:             Release the input video bitstream buffer
//
// Input Arguments:
//      stream_buf          Pointer to input video bitstream buffer
//
// Output Arguments:
//      stream_buf          Pointer to released video bitstream buffer
//
// Returns:
//     SAMPLE_STATUS_NOERR  If succeeds
*****************************************************************************/
sample_status release_input_video_buffer (sample_bitstream *stream_buf)
{
    if (stream_buf->bs_buffer) {
        free(stream_buf->bs_buffer);
        stream_buf->bs_buffer = NULL;
    }

    return SAMPLE_STATUS_NOERR;
}

/***************************************************************************
// Name:                        init_input_video_buffer
// Description:                 Initialize the input video bitstream buffer
//
// Input Arguments:
//      stream_buf              Pointer to input video bitstream buffer
//
// Output Arguments:
//      stream_buf              Pointer to initialized video bitstream buffer
//
// Returns:
//     SAMPLE_STATUS_NOERR      If succeeds
//     SAMPLE_STATUS_NOMEM_ERR  If memory allocation fails
*****************************************************************************/
sample_status init_input_video_buffer (sample_bitstream *stream_buf)
{
    /* reset the struct to zeroes */
    memset((void*)stream_buf, 0, sizeof(sample_bitstream));

    /* initialize the input video bitstream buffer which is large enough
    // to store two frames of raw data at least to reduce reload times,
    // note to allocate extra 3 bytes for the final sync code insertion */
    stream_buf->bs_buffer = (Ipp8u*)malloc(SAMPLE_VIDEO_STREAM_BUF_SIZE
        + MPEG4_SC_LEN);

    if (NULL == stream_buf->bs_buffer) {
        /* memory allocation fails */
        return SAMPLE_STATUS_NOMEM_ERR;
    }
    else {
        /* reset the newly allocated buffer to zeroes */
        memset (stream_buf->bs_buffer, 0, SAMPLE_VIDEO_STREAM_BUF_SIZE
            + MPEG4_SC_LEN);
    }

    /* set current pointer to the end of buffer for there's no data loaded
    // at beginning */

    stream_buf->bs_cur_byte = stream_buf->bs_buffer
        + SAMPLE_VIDEO_STREAM_BUF_SIZE;
    stream_buf->bs_cur_bitoffset = 0;
    stream_buf->bs_bytelen = 0;

    return SAMPLE_STATUS_NOERR;
}

/***************************************************************************
// Name:                    load_video_buffer
// Description:             Load input video bitstream into buffer
//
// Input Arguments:
//      stream_buf          Pointer to the video bitstream buffer
//      fpin                Pointer to the input file stream
//
// Output Arguments:
//      stream_buf          Pointer to updated video bitstream buffer
//
// Returns:
//      SAMPLE_STATUS_NOERR If succeeds
//      SAMPLE_STATUS_ERR   If no data read from the file stream
*****************************************************************************/
sample_status load_video_buffer(sample_bitstream *stream_buf, FILE *fpin)
{
    int     offset; 
    int     remain_len;
    
    offset = stream_buf->bs_cur_byte - stream_buf->bs_buffer;
    remain_len = SAMPLE_VIDEO_STREAM_BUF_SIZE - offset;
    
    /* round the buffer */
    if (0 != remain_len) {
        memcpy (stream_buf->bs_buffer, stream_buf->bs_cur_byte, remain_len);
    }
    
    /* fill up the buffer by loading new data into the buffer */
    stream_buf->bs_bytelen = remain_len + fread(stream_buf->bs_buffer
        + remain_len, 1, offset, fpin);

    /* no new data loaded */
    if (stream_buf->bs_bytelen == remain_len) {
        return SAMPLE_STATUS_ERR;
    }
    
    stream_buf->bs_cur_byte = stream_buf->bs_buffer;    
    return SAMPLE_STATUS_NOERR;
}