FFmpeg源码分析：av_parser_parse2

解析报文

/**
 * Parse a packet.
 *
 * @param s             parser context. 解析器上下文
 * @param avctx         codec context. 解码器上下文
 * @param poutbuf       set to pointer to parsed buffer or NULL if not yet finished. 输出数据地址
 * @param poutbuf_size  set to size of parsed buffer or zero if not yet finished. 输出数据大小
 * @param buf           input buffer. 输入数据
 * @param buf_size      buffer size in bytes without the padding. I.e. the full buffer 输入数据大小
                        size is assumed to be buf_size + AV_INPUT_BUFFER_PADDING_SIZE.
                        To signal EOF, this should be 0 (so that the last frame
                        can be output).
 * @param pts           input presentation timestamp.
 * @param dts           input decoding timestamp.
 * @param pos           input byte position in stream.
 * @return the number of bytes of the input bitstream used. 返回使用数据大小
 *
 * Example:
 * @code
 *   while(in_len){
 *       len = av_parser_parse2(myparser, AVCodecContext, &data, &size,
 *                                        in_data, in_len,
 *                                        pts, dts, pos);
 *       in_data += len;
 *       in_len  -= len;
 *
 *       if(size)
 *          decode_frame(data, size);
 *   }
 * @endcode
 */
int av_parser_parse2(AVCodecParserContext *s,
                     AVCodecContext *avctx,
                     uint8_t **poutbuf, int *poutbuf_size,
                     const uint8_t *buf, int buf_size,
                     int64_t pts, int64_t dts,
                     int64_t pos);

实现

int av_parser_parse2(AVCodecParserContext *s, AVCodecContext *avctx,
                     uint8_t **poutbuf, int *poutbuf_size,
                     const uint8_t *buf, int buf_size,
                     int64_t pts, int64_t dts, int64_t pos)
{
    int index, i;
    uint8_t dummy_buf[AV_INPUT_BUFFER_PADDING_SIZE];

    av_assert1(avctx->codec_id != AV_CODEC_ID_NONE);

    /* Parsers only work for the specified codec ids. */
    av_assert1(avctx->codec_id == s->parser->codec_ids[0] ||
               avctx->codec_id == s->parser->codec_ids[1] ||
               avctx->codec_id == s->parser->codec_ids[2] ||
               avctx->codec_id == s->parser->codec_ids[3] ||
               avctx->codec_id == s->parser->codec_ids[4]);

    if (!(s->flags & PARSER_FLAG_FETCHED_OFFSET)) {
        s->next_frame_offset =
        s->cur_offset        = pos;
        s->flags            |= PARSER_FLAG_FETCHED_OFFSET;
    }

    if (buf_size == 0) {
        /* padding is always necessary even if EOF, so we add it here */
        memset(dummy_buf, 0, sizeof(dummy_buf));
        buf = dummy_buf;
    } else if (s->cur_offset + buf_size != s->cur_frame_end[s->cur_frame_start_index]) { /* skip remainder packets */
        /* add a new packet descriptor */
        i = (s->cur_frame_start_index + 1) & (AV_PARSER_PTS_NB - 1);
        s->cur_frame_start_index = i;
        s->cur_frame_offset[i]   = s->cur_offset;
        s->cur_frame_end[i]      = s->cur_offset + buf_size;
        s->cur_frame_pts[i]      = pts;
        s->cur_frame_dts[i]      = dts;
        s->cur_frame_pos[i]      = pos;
    }

    if (s->fetch_timestamp) {
        s->fetch_timestamp = 0;
        s->last_pts        = s->pts;
        s->last_dts        = s->dts;
        s->last_pos        = s->pos;
        ff_fetch_timestamp(s, 0, 0, 0);
    }
    /* WARNING: the returned index can be negative */
    index = s->parser->parser_parse(s, avctx, (const uint8_t **) poutbuf,
                                    poutbuf_size, buf, buf_size);
    av_assert0(index > -0x20000000); // The API does not allow returning AVERROR codes
#define FILL(name) if(s->name > 0 && avctx->name <= 0) avctx->name = s->name
    if (avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
        FILL(field_order);
    }

    /* update the file pointer */
    if (*poutbuf_size) {
        /* fill the data for the current frame */
        s->frame_offset = s->next_frame_offset;

        /* offset of the next frame */
        s->next_frame_offset = s->cur_offset + index;
        s->fetch_timestamp   = 1;
    }
    if (index < 0)
        index = 0;
    s->cur_offset += index;
    return index;
}

这里就是调对应的解析器解析数据，返回使用的数据大小。