int ff_h261_handle_packet(AVFormatContext *ctx, PayloadContext *data, AVStream *st, AVPacket *pkt, uint32_t *timestamp, const uint8_t *buf, int len, uint16_t seq, int flags) { int sbit, ebit, gobn, mbap, quant; int res; //av_log(ctx, AV_LOG_DEBUG, "got h261 RTP packet with time: %u\n", timestamp); /* drop data of previous packets in case of non-continuous (loss) packet stream */ if (data->buf && data->timestamp != *timestamp) { h261_free_dyn_buffer(&data->buf); } /* sanity check for size of input packet */ if (len < 5 /* 4 bytes header and 1 byte payload at least */) { av_log(ctx, AV_LOG_ERROR, "Too short H.261 RTP packet\n"); return AVERROR_INVALIDDATA; } /* decode the H.261 payload header according to section 4.1 of RFC 4587: (uses 4 bytes between RTP header and H.261 stream per packet) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Start bit position (SBIT): 3 bits End bit position (EBIT): 3 bits INTRA-frame encoded data (I): 1 bit Motion Vector flag (V): 1 bit GOB number (GOBN): 4 bits Macroblock address predictor (MBAP): 5 bits Quantizer (QUANT): 5 bits Horizontal motion vector data (HMVD): 5 bits Vertical motion vector data (VMVD): 5 bits */ sbit = (buf[0] >> 5) & 0x07; ebit = (buf[0] >> 2) & 0x07; gobn = (buf[1] >> 4) & 0x0f; mbap = ((buf[1] << 1) & 0x1e) | ((buf[1] >> 7) & 0x01); quant = (buf[1] >> 4) & 0x0f; /* pass the H.261 payload header and continue with the actual payload */ buf += RTP_H261_PAYLOAD_HEADER_SIZE; len -= RTP_H261_PAYLOAD_HEADER_SIZE; /* start frame buffering with new dynamic buffer */ if (!data->buf) { /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, uqnat=0 */ if (!gobn && !sbit && !mbap && !quant){ res = avio_open_dyn_buf(&data->buf); if (res < 0) return res; /* update the timestamp in the frame packet with the one from the RTP packet */ data->timestamp = *timestamp; } else { /* frame not started yet, need more packets */ return AVERROR(EAGAIN); } } /* do the "byte merging" at the boundaries of two consecutive frame fragments */ if (data->endbyte_bits || sbit) { if (data->endbyte_bits == sbit) { data->endbyte |= buf[0] & (0xff >> sbit); data->endbyte_bits = 0; buf++; len--; avio_w8(data->buf, data->endbyte); } else { /* ebit/sbit values inconsistent, assuming packet loss */ GetBitContext gb; init_get_bits(&gb, buf, len*8 - ebit); skip_bits(&gb, sbit); if (data->endbyte_bits) { data->endbyte |= get_bits(&gb, 8 - data->endbyte_bits); avio_w8(data->buf, data->endbyte); } while (get_bits_left(&gb) >= 8) avio_w8(data->buf, get_bits(&gb, 8)); data->endbyte_bits = get_bits_left(&gb); if (data->endbyte_bits) data->endbyte = get_bits(&gb, data->endbyte_bits) << (8 - data->endbyte_bits); ebit = 0; len = 0; } } if (ebit) { if (len > 0) avio_write(data->buf, buf, len - 1); data->endbyte_bits = 8 - ebit; data->endbyte = buf[len - 1] & (0xff << ebit); } else { avio_write(data->buf, buf, len); } /* RTP marker bit means: last fragment of current frame was received; otherwise, an additional fragment is needed for the current frame */ if (!(flags & RTP_FLAG_MARKER)) return AVERROR(EAGAIN); /* write the completed last byte from the "byte merging" */ if (data->endbyte_bits) avio_w8(data->buf, data->endbyte); data->endbyte_bits = 0; /* close frame buffering and create resulting A/V packet */ res = ff_rtp_finalize_packet(pkt, &data->buf, st->index); if (res < 0) return res; return 0; }