/*

 * RTP parser for H.261 payload format (RFC 4587)

 * Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com>

 *

 * 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 "libavcodec/get_bits.h"

#include "avformat.h"

#include "avio_internal.h"

#include "rtpdec_formats.h"

#define RTP_H261_PAYLOAD_HEADER_SIZE 4

struct PayloadContext {

    AVIOContext *buf;

    uint8_t      endbyte;

    int          endbyte_bits;

    uint32_t     timestamp;

};

static av_cold void h261_close_context(PayloadContext *pl_ctx)

{

    /* return if context is invalid */

    if (!pl_ctx)

        return;

    /* free buffer if it is valid */

    ffio_free_dyn_buf(&pl_ctx->buf);

}

static int h261_handle_packet(AVFormatContext *ctx, PayloadContext *rtp_h261_ctx,

                              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;

    /* drop data of previous packets in case of non-continuous (lossy) packet stream */

    if (rtp_h261_ctx->buf && rtp_h261_ctx->timestamp != *timestamp) {

        ffio_free_dyn_buf(&rtp_h261_ctx->buf);

        rtp_h261_ctx->endbyte_bits = 0;

    }

    /* sanity check for size of input packet: 1 byte payload at least */

    if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) {

        av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len);

        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[2] >> 7) & 0x01);

    quant =  (buf[2] >> 2) & 0x1f;

    /* 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 (!rtp_h261_ctx->buf) {

        /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, quant=0 */

        if (!gobn && !sbit && !mbap && !quant) {

            res = avio_open_dyn_buf(&rtp_h261_ctx->buf);

            if (res < 0)

                return res;

            /* update the timestamp in the frame packet with the one from the RTP packet */

            rtp_h261_ctx->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 (rtp_h261_ctx->endbyte_bits || sbit) {

        if (rtp_h261_ctx->endbyte_bits == sbit) {

            rtp_h261_ctx->endbyte     |= buf[0] & (0xff >> sbit);

            rtp_h261_ctx->endbyte_bits = 0;

            buf++;

            len--;

            avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);

        } else {

            /* ebit/sbit values inconsistent, assuming packet loss */

            GetBitContext gb;

            res = init_get_bits(&gb, buf, len*8 - ebit);

            if (res < 0)

                return res;

            skip_bits(&gb, sbit);

            if (rtp_h261_ctx->endbyte_bits) {

                rtp_h261_ctx->endbyte |= get_bits(&gb, 8 - rtp_h261_ctx->endbyte_bits);

                avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);

            }

            while (get_bits_left(&gb) >= 8)

                avio_w8(rtp_h261_ctx->buf, get_bits(&gb, 8));

            rtp_h261_ctx->endbyte_bits = get_bits_left(&gb);

            if (rtp_h261_ctx->endbyte_bits)

                rtp_h261_ctx->endbyte = get_bits(&gb, rtp_h261_ctx->endbyte_bits) <<

                                        (8 - rtp_h261_ctx->endbyte_bits);

            ebit = 0;

            len  = 0;

        }

    }

    if (ebit) {

        if (len > 0)

            avio_write(rtp_h261_ctx->buf, buf, len - 1);

        rtp_h261_ctx->endbyte_bits = 8 - ebit;

        rtp_h261_ctx->endbyte      = buf[len - 1] & (0xff << ebit);

    } else {

        avio_write(rtp_h261_ctx->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 (rtp_h261_ctx->endbyte_bits)

        avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);

    rtp_h261_ctx->endbyte_bits = 0;

    /* close frame buffering and create resulting A/V packet */

    res = ff_rtp_finalize_packet(pkt, &rtp_h261_ctx->buf, st->index);

    if (res < 0)

        return res;

    return 0;

}

const RTPDynamicProtocolHandler ff_h261_dynamic_handler = {

    .enc_name          = "H261",

    .codec_type        = AVMEDIA_TYPE_VIDEO,

    .codec_id          = AV_CODEC_ID_H261,

    .need_parsing      = AVSTREAM_PARSE_FULL,

    .priv_data_size    = sizeof(PayloadContext),

    .close             = h261_close_context,

    .parse_packet      = h261_handle_packet,

    .static_payload_id = 31,

};