h264_mp4toannexb_bsf.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

/*
 * Copyright (c) 2007 Benoit Fouet <[e-mail]>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg 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 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg 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 FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "avcodec.h"

typedef struct H264BSFContext {
    uint8_t  length_size;
    uint8_t  first_idr;
    uint8_t *sps_pps_data;
    uint32_t size;
} H264BSFContext;

static void alloc_and_copy(uint8_t **poutbuf,          int *poutbuf_size,
                           const uint8_t *sps_pps, uint32_t sps_pps_size,
                           const uint8_t *in,      uint32_t in_size) {
    uint32_t offset = *poutbuf_size;
    uint8_t nal_header_size = offset ? 3 : 4;

    *poutbuf_size += sps_pps_size+in_size+nal_header_size;
    *poutbuf = av_realloc(*poutbuf, *poutbuf_size);
    if (sps_pps)
        memcpy(*poutbuf+offset, sps_pps, sps_pps_size);
    memcpy(*poutbuf+sps_pps_size+nal_header_size+offset, in, in_size);
    if (!offset)
        AV_WB32(*poutbuf+sps_pps_size, 1);
    else {
        (*poutbuf+offset)[0] = (*poutbuf+offset)[1] = 0;
        (*poutbuf+offset)[2] = 1;
    }
}

static int h264_mp4toannexb_filter(AVBitStreamFilterContext *bsfc,
                                   AVCodecContext *avctx, const char *args,
                                   uint8_t  **poutbuf, int *poutbuf_size,
                                   const uint8_t *buf, int      buf_size,
                                   int keyframe) {
    H264BSFContext *ctx = bsfc->priv_data;
    uint8_t unit_type;
    uint32_t nal_size, cumul_size = 0;

    /* nothing to filter */
    if (!avctx->extradata || avctx->extradata_size < 6) {
        *poutbuf = (uint8_t*) buf;
        *poutbuf_size = buf_size;
        return 0;
    }

    /* retrieve sps and pps NAL units from extradata */
    if (!ctx->sps_pps_data) {
        uint16_t unit_size;
        uint32_t total_size = 0;
        uint8_t *out = NULL, unit_nb, sps_done = 0;
        const uint8_t *extradata = avctx->extradata+4;
        static const uint8_t nalu_header[4] = {0, 0, 0, 1};

        /* retrieve length coded size */
        ctx->length_size = (*extradata++ & 0x3) + 1;
        if (ctx->length_size == 3)
            return AVERROR(EINVAL);

        /* retrieve sps and pps unit(s) */
        unit_nb = *extradata++ & 0x1f; /* number of sps unit(s) */
        if (!unit_nb) {
            unit_nb = *extradata++; /* number of pps unit(s) */
            sps_done++;
        }
        while (unit_nb--) {
            unit_size = AV_RB16(extradata);
            total_size += unit_size+4;
            if (extradata+2+unit_size > avctx->extradata+avctx->extradata_size) {
                av_free(out);
                return AVERROR(EINVAL);
            }
            out = av_realloc(out, total_size);
            if (!out)
                return AVERROR(ENOMEM);
            memcpy(out+total_size-unit_size-4, nalu_header, 4);
            memcpy(out+total_size-unit_size,   extradata+2, unit_size);
            extradata += 2+unit_size;

            if (!unit_nb && !sps_done++)
                unit_nb = *extradata++; /* number of pps unit(s) */
        }

        ctx->sps_pps_data = out;
        ctx->size = total_size;
        ctx->first_idr = 1;
    }

    *poutbuf_size = 0;
    *poutbuf = NULL;
    do {
        if (ctx->length_size == 1)
            nal_size = buf[0];
        else if (ctx->length_size == 2)
            nal_size = AV_RB16(buf);
        else
            nal_size = AV_RB32(buf);

        buf += ctx->length_size;
        unit_type = *buf & 0x1f;

        /* prepend only to the first type 5 NAL unit of an IDR picture */
        if (ctx->first_idr && unit_type == 5) {
            alloc_and_copy(poutbuf, poutbuf_size,
                           ctx->sps_pps_data, ctx->size,
                           buf, nal_size);
            ctx->first_idr = 0;
        }
        else {
            alloc_and_copy(poutbuf, poutbuf_size,
                           NULL, 0,
                           buf, nal_size);
            if (!ctx->first_idr && unit_type == 1)
                ctx->first_idr = 1;
        }

        buf += nal_size;
        cumul_size += nal_size + ctx->length_size;
    } while (cumul_size < buf_size);

    return 1;
}

static void h264_mp4toannexb_close(AVBitStreamFilterContext *bsfc)
{
    H264BSFContext *ctx = bsfc->priv_data;
    av_freep(&ctx->sps_pps_data);
}

AVBitStreamFilter h264_mp4toannexb_bsf = {
    "h264_mp4toannexb",
    sizeof(H264BSFContext),
    h264_mp4toannexb_filter,
    h264_mp4toannexb_close,
};