204 lines
6.8 KiB
C
204 lines
6.8 KiB
C
/*
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* RTP parser for H.261 payload format (RFC 4587)
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* Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include "avformat.h"
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#include "rtpdec_formats.h"
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#include "libavcodec/get_bits.h"
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#define RTP_H261_PAYLOAD_HEADER_SIZE 4
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struct PayloadContext {
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AVIOContext *buf;
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uint8_t endbyte;
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int endbyte_bits;
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uint32_t timestamp;
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};
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static av_cold PayloadContext *h261_new_context(void)
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{
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return av_mallocz(sizeof(PayloadContext));
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}
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static void h261_free_dyn_buffer(AVIOContext **dyn_buf)
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{
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uint8_t *ptr_dyn_buffer;
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avio_close_dyn_buf(*dyn_buf, &ptr_dyn_buffer);
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av_free(ptr_dyn_buffer);
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*dyn_buf = NULL;
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}
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static av_cold void h261_free_context(PayloadContext *pl_ctx)
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{
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/* return if context is invalid */
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if (!pl_ctx)
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return;
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/* free buffer if it is valid */
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if (pl_ctx->buf) {
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h261_free_dyn_buffer(&pl_ctx->buf);
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}
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/* free context */
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av_free(pl_ctx);
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}
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static av_cold int h261_init(AVFormatContext *ctx, int st_index,
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PayloadContext *data)
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{
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//av_log(ctx, AV_LOG_DEBUG, "h261_init() for stream %d\n", st_index);
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if (st_index < 0)
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return 0;
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ctx->streams[st_index]->need_parsing = AVSTREAM_PARSE_FULL;
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return 0;
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}
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int ff_h261_handle_packet(AVFormatContext *ctx, PayloadContext *data,
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AVStream *st, AVPacket *pkt, uint32_t *timestamp,
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const uint8_t *buf, int len, uint16_t seq, int flags)
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{
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int sbit, ebit, gobn, mbap, quant;
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int res;
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/* drop data of previous packets in case of non-continuous (loss) packet stream */
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if (data->buf && data->timestamp != *timestamp) {
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h261_free_dyn_buffer(&data->buf);
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}
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/* sanity check for size of input packet: 1 byte payload at least */
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if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) {
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av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len);
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return AVERROR_INVALIDDATA;
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}
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/*
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decode the H.261 payload header according to section 4.1 of RFC 4587:
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(uses 4 bytes between RTP header and H.261 stream per packet)
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0 1 2 3
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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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Start bit position (SBIT): 3 bits
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End bit position (EBIT): 3 bits
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INTRA-frame encoded data (I): 1 bit
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Motion Vector flag (V): 1 bit
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GOB number (GOBN): 4 bits
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Macroblock address predictor (MBAP): 5 bits
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Quantizer (QUANT): 5 bits
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Horizontal motion vector data (HMVD): 5 bits
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Vertical motion vector data (VMVD): 5 bits
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*/
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sbit = (buf[0] >> 5) & 0x07;
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ebit = (buf[0] >> 2) & 0x07;
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gobn = (buf[1] >> 4) & 0x0f;
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mbap = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01);
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quant = (buf[2] >> 2) & 0x1f;
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/* pass the H.261 payload header and continue with the actual payload */
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buf += RTP_H261_PAYLOAD_HEADER_SIZE;
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len -= RTP_H261_PAYLOAD_HEADER_SIZE;
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/* start frame buffering with new dynamic buffer */
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if (!data->buf) {
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/* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, uqnat=0 */
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if (!gobn && !sbit && !mbap && !quant){
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res = avio_open_dyn_buf(&data->buf);
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if (res < 0)
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return res;
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/* update the timestamp in the frame packet with the one from the RTP packet */
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data->timestamp = *timestamp;
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} else {
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/* frame not started yet, need more packets */
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return AVERROR(EAGAIN);
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}
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}
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/* do the "byte merging" at the boundaries of two consecutive frame fragments */
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if (data->endbyte_bits || sbit) {
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if (data->endbyte_bits == sbit) {
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data->endbyte |= buf[0] & (0xff >> sbit);
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data->endbyte_bits = 0;
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buf++;
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len--;
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avio_w8(data->buf, data->endbyte);
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} else {
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/* ebit/sbit values inconsistent, assuming packet loss */
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GetBitContext gb;
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init_get_bits(&gb, buf, len*8 - ebit);
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skip_bits(&gb, sbit);
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if (data->endbyte_bits) {
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data->endbyte |= get_bits(&gb, 8 - data->endbyte_bits);
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avio_w8(data->buf, data->endbyte);
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}
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while (get_bits_left(&gb) >= 8)
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avio_w8(data->buf, get_bits(&gb, 8));
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data->endbyte_bits = get_bits_left(&gb);
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if (data->endbyte_bits)
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data->endbyte = get_bits(&gb, data->endbyte_bits) <<
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(8 - data->endbyte_bits);
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ebit = 0;
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len = 0;
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}
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}
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if (ebit) {
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if (len > 0)
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avio_write(data->buf, buf, len - 1);
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data->endbyte_bits = 8 - ebit;
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data->endbyte = buf[len - 1] & (0xff << ebit);
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} else {
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avio_write(data->buf, buf, len);
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}
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/* RTP marker bit means: last fragment of current frame was received;
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otherwise, an additional fragment is needed for the current frame */
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if (!(flags & RTP_FLAG_MARKER))
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return AVERROR(EAGAIN);
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/* write the completed last byte from the "byte merging" */
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if (data->endbyte_bits)
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avio_w8(data->buf, data->endbyte);
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data->endbyte_bits = 0;
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/* close frame buffering and create resulting A/V packet */
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res = ff_rtp_finalize_packet(pkt, &data->buf, st->index);
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if (res < 0)
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return res;
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return 0;
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}
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RTPDynamicProtocolHandler ff_h261_dynamic_handler = {
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.enc_name = "H261",
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.codec_type = AVMEDIA_TYPE_VIDEO,
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.codec_id = AV_CODEC_ID_H261,
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.init = h261_init,
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.parse_packet = ff_h261_handle_packet,
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.alloc = h261_new_context,
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.free = h261_free_context,
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.static_payload_id = 31,
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};
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