mpeg.c

F:图像处理资料264264书籍ffmpeg-0.4.9-pre1VideoStream.rar 一个视频解压缩源代码

/*
 * MPEG1/2 mux/demux
 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
#include "avformat.h"

#define MAX_PAYLOAD_SIZE 4096
//#define DEBUG_SEEK

#undef NDEBUG
#include <assert.h>

typedef struct {
    uint8_t buffer[MAX_PAYLOAD_SIZE];
    int buffer_ptr;
    int nb_frames;    /* number of starting frame encountered (AC3) */
    int frame_start_offset; /* starting offset of the frame + 1 (0 if none) */
    uint8_t id;
    int max_buffer_size; /* in bytes */
    int packet_number;
    int64_t start_pts;
    int64_t start_dts;
    uint8_t lpcm_header[3];
    int lpcm_align;
} StreamInfo;

typedef struct {
    int packet_size; /* required packet size */
    int packet_number;
    int pack_header_freq;     /* frequency (in packets^-1) at which we send pack headers */
    int system_header_freq;
    int system_header_size;
    int mux_rate; /* bitrate in units of 50 bytes/s */
    /* stream info */
    int audio_bound;
    int video_bound;
    int is_mpeg2;
    int is_vcd;
    int is_svcd;
    int scr_stream_index; /* stream from which the system clock is
                             computed (VBR case) */
    int64_t last_scr; /* current system clock */

    double vcd_padding_bitrate;
    int64_t vcd_padding_bytes_written;

} MpegMuxContext;

#define PACK_START_CODE             ((unsigned int)0x000001ba)
#define SYSTEM_HEADER_START_CODE    ((unsigned int)0x000001bb)
#define SEQUENCE_END_CODE           ((unsigned int)0x000001b7)
#define PACKET_START_CODE_MASK      ((unsigned int)0xffffff00)
#define PACKET_START_CODE_PREFIX    ((unsigned int)0x00000100)
#define ISO_11172_END_CODE          ((unsigned int)0x000001b9)
  
/* mpeg2 */
#define PROGRAM_STREAM_MAP 0x1bc
#define PRIVATE_STREAM_1   0x1bd
#define PADDING_STREAM     0x1be
#define PRIVATE_STREAM_2   0x1bf


#define AUDIO_ID 0xc0
#define VIDEO_ID 0xe0
#define AC3_ID   0x80
#define LPCM_ID  0xa0

static const int lpcm_freq_tab[4] = { 48000, 96000, 44100, 32000 };

#ifdef CONFIG_ENCODERS
static AVOutputFormat mpeg1system_mux;
static AVOutputFormat mpeg1vcd_mux;
static AVOutputFormat mpeg2vob_mux;
static AVOutputFormat mpeg2svcd_mux;

static int put_pack_header(AVFormatContext *ctx, 
                           uint8_t *buf, int64_t timestamp)
{
    MpegMuxContext *s = ctx->priv_data;
    PutBitContext pb;
    
    init_put_bits(&pb, buf, 128);

    put_bits(&pb, 32, PACK_START_CODE);
    if (s->is_mpeg2) {
        put_bits(&pb, 2, 0x1);
    } else {
        put_bits(&pb, 4, 0x2);
    }
    put_bits(&pb, 3, (uint32_t)((timestamp >> 30) & 0x07));
    put_bits(&pb, 1, 1);
    put_bits(&pb, 15, (uint32_t)((timestamp >> 15) & 0x7fff));
    put_bits(&pb, 1, 1);
    put_bits(&pb, 15, (uint32_t)((timestamp) & 0x7fff));
    put_bits(&pb, 1, 1);
    if (s->is_mpeg2) {
        /* clock extension */
        put_bits(&pb, 9, 0);
    }
    put_bits(&pb, 1, 1);
    put_bits(&pb, 22, s->mux_rate);
    put_bits(&pb, 1, 1);
    if (s->is_mpeg2) {
        put_bits(&pb, 1, 1);
        put_bits(&pb, 5, 0x1f); /* reserved */
        put_bits(&pb, 3, 0); /* stuffing length */
    }
    flush_put_bits(&pb);
    return pbBufPtr(&pb) - pb.buf;
}

static int put_system_header(AVFormatContext *ctx, uint8_t *buf,int only_for_stream_id)
{
    MpegMuxContext *s = ctx->priv_data;
    int size, rate_bound, i, private_stream_coded, id;
    PutBitContext pb;

    init_put_bits(&pb, buf, 128);

    put_bits(&pb, 32, SYSTEM_HEADER_START_CODE);
    put_bits(&pb, 16, 0);
    put_bits(&pb, 1, 1);
    
    rate_bound = s->mux_rate; /* maximum bit rate of the multiplexed stream */
    put_bits(&pb, 22, rate_bound);
    put_bits(&pb, 1, 1); /* marker */
    if (s->is_vcd && only_for_stream_id==VIDEO_ID) {
        /* This header applies only to the video stream (see VCD standard p. IV-7)*/
        put_bits(&pb, 6, 0);
    } else
        put_bits(&pb, 6, s->audio_bound);

    if (s->is_vcd) {
        /* see VCD standard, p. IV-7*/
        put_bits(&pb, 1, 0); 
        put_bits(&pb, 1, 1);
    } else {
        put_bits(&pb, 1, 0); /* variable bitrate*/
        put_bits(&pb, 1, 0); /* non constrainted bit stream */
    }
    
    if (s->is_vcd) {
        /* see VCD standard p IV-7 */
        put_bits(&pb, 1, 1); /* audio locked */
        put_bits(&pb, 1, 1); /* video locked */
    } else {
        put_bits(&pb, 1, 0); /* audio locked */
        put_bits(&pb, 1, 0); /* video locked */
    }

    put_bits(&pb, 1, 1); /* marker */

    if (s->is_vcd && only_for_stream_id==AUDIO_ID) {
        /* This header applies only to the audio stream (see VCD standard p. IV-7)*/
        put_bits(&pb, 5, 0);
    } else
        put_bits(&pb, 5, s->video_bound);

    put_bits(&pb, 8, 0xff); /* reserved byte */
    
    /* audio stream info */
    private_stream_coded = 0;
    for(i=0;i<ctx->nb_streams;i++) {
        StreamInfo *stream = ctx->streams[i]->priv_data;
        
        /* For VCDs, only include the stream info for the stream
           that the pack which contains this system belongs to.
           (see VCD standard p. IV-7) */
        if ( !s->is_vcd || stream->id==only_for_stream_id
            || only_for_stream_id==0) {

            id = stream->id;
            if (id < 0xc0) {
                /* special case for private streams (AC3 use that) */
                if (private_stream_coded)
                    continue;
                private_stream_coded = 1;
                id = 0xbd;
            }
            put_bits(&pb, 8, id); /* stream ID */
            put_bits(&pb, 2, 3);
            if (id < 0xe0) {
                /* audio */
                put_bits(&pb, 1, 0);
                put_bits(&pb, 13, stream->max_buffer_size / 128);
            } else {
                /* video */
                put_bits(&pb, 1, 1);
                put_bits(&pb, 13, stream->max_buffer_size / 1024);
            }
        }
    }
    flush_put_bits(&pb);
    size = pbBufPtr(&pb) - pb.buf;
    /* patch packet size */
    buf[4] = (size - 6) >> 8;
    buf[5] = (size - 6) & 0xff;

    return size;
}

static int get_system_header_size(AVFormatContext *ctx)
{
    int buf_index, i, private_stream_coded;
    StreamInfo *stream;

    buf_index = 12;
    private_stream_coded = 0;
    for(i=0;i<ctx->nb_streams;i++) {
        stream = ctx->streams[i]->priv_data;
        if (stream->id < 0xc0) {
            if (private_stream_coded)
                continue;
            private_stream_coded = 1;
        }
        buf_index += 3;
    }
    return buf_index;
}

static int mpeg_mux_init(AVFormatContext *ctx)
{
    MpegMuxContext *s = ctx->priv_data;
    int bitrate, i, mpa_id, mpv_id, ac3_id, lpcm_id, j;
    AVStream *st;
    StreamInfo *stream;
    int audio_bitrate;
    int video_bitrate;

    s->packet_number = 0;
    s->is_vcd = (ctx->oformat == &mpeg1vcd_mux);
    s->is_svcd = (ctx->oformat == &mpeg2svcd_mux);
    s->is_mpeg2 = (ctx->oformat == &mpeg2vob_mux || ctx->oformat == &mpeg2svcd_mux);
    
    if (s->is_vcd || s->is_svcd)
        s->packet_size = 2324; /* VCD/SVCD packet size */
    else
        s->packet_size = 2048;

    s->vcd_padding_bytes_written = 0;
    s->vcd_padding_bitrate=0;
        
    s->audio_bound = 0;
    s->video_bound = 0;
    mpa_id = AUDIO_ID;
    ac3_id = AC3_ID;
    mpv_id = VIDEO_ID;
    lpcm_id = LPCM_ID;
    s->scr_stream_index = -1;
    for(i=0;i<ctx->nb_streams;i++) {
        st = ctx->streams[i];
        stream = av_mallocz(sizeof(StreamInfo));
        if (!stream)
            goto fail;
        st->priv_data = stream;

        switch(st->codec.codec_type) {
        case CODEC_TYPE_AUDIO:
            if (st->codec.codec_id == CODEC_ID_AC3) {
                stream->id = ac3_id++;
            } else if (st->codec.codec_id == CODEC_ID_PCM_S16BE) {
                stream->id = lpcm_id++;
                for(j = 0; j < 4; j++) {
                    if (lpcm_freq_tab[j] == st->codec.sample_rate)
                        break;
                }
                if (j == 4)
                    goto fail;
                if (st->codec.channels > 8)
                    return -1;
                stream->lpcm_header[0] = 0x0c;
                stream->lpcm_header[1] = (st->codec.channels - 1) | (j << 4);
                stream->lpcm_header[2] = 0x80;
                stream->lpcm_align = st->codec.channels * 2;
            } else {
                stream->id = mpa_id++;
            }

            /* This value HAS to be used for VCD (see VCD standard, p. IV-7).
               Right now it is also used for everything else.*/
            stream->max_buffer_size = 4 * 1024; 
            s->audio_bound++;
            break;
        case CODEC_TYPE_VIDEO:
            /* by default, video is used for the SCR computation */
            if (s->scr_stream_index == -1)
                s->scr_stream_index = i;
            stream->id = mpv_id++;
            if (s->is_vcd)
                /* see VCD standard, p. IV-7*/
                stream->max_buffer_size = 46 * 1024; 
            else
                /* This value HAS to be used for SVCD (see SVCD standard, p. 26 V.2.3.2).
                   Right now it is also used for everything else.*/
                stream->max_buffer_size = 230 * 1024; 
            s->video_bound++;
            break;
        default:
            av_abort();
        }
    }
    /* if no SCR, use first stream (audio) */
    if (s->scr_stream_index == -1)
        s->scr_stream_index = 0;

    bitrate = 0;
    audio_bitrate = 0;
    video_bitrate = 0;
    for(i=0;i<ctx->nb_streams;i++) {
        st = ctx->streams[i];
        stream = (StreamInfo*) st->priv_data;
        
        bitrate += st->codec.bit_rate;

        if (stream->id==AUDIO_ID)
            audio_bitrate += st->codec.bit_rate;
        else if (stream->id==VIDEO_ID)
            video_bitrate += st->codec.bit_rate;
    }

    if (s->is_vcd) {
        double overhead_rate;

        /* The VCD standard mandates that the mux_rate field is 3528
           (see standard p. IV-6).
           The value is actually "wrong", i.e. if you calculate
           it using the normal formula and the 75 sectors per second transfer
           rate you get a different value because the real pack size is 2324,
           not 2352. But the standard explicitly specifies that the mux_rate
           field in the header must have this value.*/
        s->mux_rate=2352 * 75 / 50;    /* = 3528*/

        /* The VCD standard states that the muxed stream must be
           exactly 75 packs / second (the data rate of a single speed cdrom).
           Since the video bitrate (probably 1150000 bits/sec) will be below
           the theoretical maximum we have to add some padding packets
           to make up for the lower data rate.
           (cf. VCD standard p. IV-6 )*/

        /* Add the header overhead to the data rate.
           2279 data bytes per audio pack, 2294 data bytes per video pack*/
        overhead_rate = ((audio_bitrate / 8.0) / 2279) * (2324 - 2279);
        overhead_rate += ((video_bitrate / 8.0) / 2294) * (2324 - 2294);
        overhead_rate *= 8;
        
        /* Add padding so that the full bitrate is 2324*75 bytes/sec */
        s->vcd_padding_bitrate = 2324 * 75 * 8 - (bitrate + overhead_rate);

    } else {
        /* we increase slightly the bitrate to take into account the
           headers. XXX: compute it exactly */
        bitrate += 2000;
        s->mux_rate = (bitrate + (8 * 50) - 1) / (8 * 50);
    }