annotate ffmpeg/libavformat/rtpdec_vp8.c @ 13:844d341cf643 tip

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/*
 * RTP VP8 Depacketizer
 * Copyright (c) 2010 Josh Allmann
 * Copyright (c) 2012 Martin Storsjo
 *
 * 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
 */

/**
 * @file
 * @brief RTP support for the VP8 payload
 * @author Josh Allmann <[e-mail]>
 * @see http://tools.ietf.org/html/draft-ietf-payload-vp8-05
 */

#include "libavcodec/bytestream.h"

#include "rtpdec_formats.h"

struct PayloadContext {
    AVIOContext *data;
    uint32_t     timestamp;
    int          is_keyframe;
    /* If sequence_ok is set, we keep returning data (even if we might have
     * lost some data, but we haven't lost any too critical data that would
     * cause the decoder to desynchronize and output random garbage).
     */
    int          sequence_ok;
    int          first_part_size;
    uint16_t     prev_seq;
    int          prev_pictureid;
    int          broken_frame;
    /* If sequence_dirty is set, we have lost some data (critical or
     * non-critical) and decoding will have some sort of artefacts, and
     * we thus should request a new keyframe.
     */
    int          sequence_dirty;
    int          got_keyframe;
};

static void vp8_free_buffer(PayloadContext *vp8)
{
    uint8_t *tmp;
    if (!vp8->data)
        return;
    avio_close_dyn_buf(vp8->data, &tmp);
    av_free(tmp);
    vp8->data = NULL;
}

static int vp8_broken_sequence(AVFormatContext *ctx, PayloadContext *vp8,
                               const char *msg)
{
    vp8->sequence_ok = 0;
    av_log(ctx, AV_LOG_WARNING, "%s", msg);
    vp8_free_buffer(vp8);
    return AVERROR(EAGAIN);
}

static int vp8_handle_packet(AVFormatContext *ctx, PayloadContext *vp8,
                             AVStream *st, AVPacket *pkt, uint32_t *timestamp,
                             const uint8_t *buf, int len, uint16_t seq,
                             int flags)
{
    int start_partition, end_packet;
    int extended_bits, part_id;
    int pictureid_present = 0, tl0picidx_present = 0, tid_present = 0,
        keyidx_present = 0;
    int pictureid = -1, pictureid_mask = 0;
    int returned_old_frame = 0;
    uint32_t old_timestamp = 0;

    if (!buf) {
        if (vp8->data) {
            int ret = ff_rtp_finalize_packet(pkt, &vp8->data, st->index);
            if (ret < 0)
                return ret;
            *timestamp = vp8->timestamp;
            if (vp8->sequence_dirty)
                pkt->flags |= AV_PKT_FLAG_CORRUPT;
            return 0;
        }
        return AVERROR(EAGAIN);
    }

    if (len < 1)
        return AVERROR_INVALIDDATA;

    extended_bits   = buf[0] & 0x80;
    start_partition = buf[0] & 0x10;
    part_id         = buf[0] & 0x0f;
    end_packet      = flags & RTP_FLAG_MARKER;
    buf++;
    len--;
    if (extended_bits) {
        if (len < 1)
            return AVERROR_INVALIDDATA;
        pictureid_present = buf[0] & 0x80;
        tl0picidx_present = buf[0] & 0x40;
        tid_present       = buf[0] & 0x20;
        keyidx_present    = buf[0] & 0x10;
        buf++;
        len--;
    }
    if (pictureid_present) {
        if (len < 1)
            return AVERROR_INVALIDDATA;
        if (buf[0] & 0x80) {
            if (len < 2)
                return AVERROR_INVALIDDATA;
            pictureid = AV_RB16(buf) & 0x7fff;
            pictureid_mask = 0x7fff;
            buf += 2;
            len -= 2;
        } else {
            pictureid = buf[0] & 0x7f;
            pictureid_mask = 0x7f;
            buf++;
            len--;
        }
    }
    if (tl0picidx_present) {
        // Ignoring temporal level zero index
        buf++;
        len--;
    }
    if (tid_present || keyidx_present) {
        // Ignoring temporal layer index, layer sync bit and keyframe index
        buf++;
        len--;
    }
    if (len < 1)
        return AVERROR_INVALIDDATA;

    if (start_partition && part_id == 0 && len >= 3) {
        int res;
        int non_key = buf[0] & 0x01;
        if (!non_key) {
            vp8_free_buffer(vp8);
            // Keyframe, decoding ok again
            vp8->sequence_ok = 1;
            vp8->sequence_dirty = 0;
            vp8->got_keyframe = 1;
        } else {
            int can_continue = vp8->data && !vp8->is_keyframe &&
                               avio_tell(vp8->data) >= vp8->first_part_size;
            if (!vp8->sequence_ok)
                return AVERROR(EAGAIN);
            if (!vp8->got_keyframe)
                return vp8_broken_sequence(ctx, vp8, "Keyframe missing\n");
            if (pictureid >= 0) {
                if (pictureid != ((vp8->prev_pictureid + 1) & pictureid_mask)) {
                    return vp8_broken_sequence(ctx, vp8,
                                               "Missed a picture, sequence broken\n");
                } else {
                    if (vp8->data && !can_continue)
                        return vp8_broken_sequence(ctx, vp8,
                                                   "Missed a picture, sequence broken\n");
                }
            } else {
                uint16_t expected_seq = vp8->prev_seq + 1;
                int16_t diff = seq - expected_seq;
                if (vp8->data) {
                    // No picture id, so we can't know if missed packets
                    // contained any new frames. If diff == 0, we did get
                    // later packets from the same frame (matching timestamp),
                    // so we know we didn't miss any frame. If diff == 1 and
                    // we still have data (not flushed by the end of frame
                    // marker), the single missed packet must have been part
                    // of the same frame.
                    if ((diff == 0 || diff == 1) && can_continue) {
                        // Proceed with what we have
                    } else {
                        return vp8_broken_sequence(ctx, vp8,
                                                   "Missed too much, sequence broken\n");
                    }
                } else {
                    if (diff != 0)
                        return vp8_broken_sequence(ctx, vp8,
                                                   "Missed unknown data, sequence broken\n");
                }
            }
            if (vp8->data) {
                vp8->sequence_dirty = 1;
                if (avio_tell(vp8->data) >= vp8->first_part_size) {
                    int ret = ff_rtp_finalize_packet(pkt, &vp8->data, st->index);
                    if (ret < 0)
                        return ret;
                    pkt->flags |= AV_PKT_FLAG_CORRUPT;
                    returned_old_frame = 1;
                    old_timestamp = vp8->timestamp;
                } else {
                    // Shouldn't happen
                    vp8_free_buffer(vp8);
                }
            }
        }
        vp8->first_part_size = (AV_RL16(&buf[1]) << 3 | buf[0] >> 5) + 3;
        if ((res = avio_open_dyn_buf(&vp8->data)) < 0)
            return res;
        vp8->timestamp = *timestamp;
        vp8->broken_frame = 0;
        vp8->prev_pictureid = pictureid;
        vp8->is_keyframe = !non_key;
    } else {
        uint16_t expected_seq = vp8->prev_seq + 1;

        if (!vp8->sequence_ok)
            return AVERROR(EAGAIN);

        if (vp8->timestamp != *timestamp) {
            // Missed the start of the new frame, sequence broken
            return vp8_broken_sequence(ctx, vp8,
                                       "Received no start marker; dropping frame\n");
        }

        if (seq != expected_seq) {
            if (vp8->is_keyframe) {
                return vp8_broken_sequence(ctx, vp8,
                                           "Missed part of a keyframe, sequence broken\n");
            } else if (vp8->data && avio_tell(vp8->data) >= vp8->first_part_size) {
                vp8->broken_frame = 1;
                vp8->sequence_dirty = 1;
            } else {
                return vp8_broken_sequence(ctx, vp8,
                                           "Missed part of the first partition, sequence broken\n");
            }
        }
    }

    if (!vp8->data)
        return vp8_broken_sequence(ctx, vp8, "Received no start marker\n");

    vp8->prev_seq = seq;
    if (!vp8->broken_frame)
        avio_write(vp8->data, buf, len);

    if (returned_old_frame) {
        *timestamp = old_timestamp;
        return end_packet ? 1 : 0;
    }

    if (end_packet) {
        int ret;
        ret = ff_rtp_finalize_packet(pkt, &vp8->data, st->index);
        if (ret < 0)
            return ret;
        if (vp8->sequence_dirty)
            pkt->flags |= AV_PKT_FLAG_CORRUPT;
        return 0;
    }

    return AVERROR(EAGAIN);
}

static PayloadContext *vp8_new_context(void)
{
    PayloadContext *vp8 = av_mallocz(sizeof(PayloadContext));
    if (!vp8)
        return NULL;
    vp8->sequence_ok = 1;
    return vp8;
}

static void vp8_free_context(PayloadContext *vp8)
{
    vp8_free_buffer(vp8);
    av_free(vp8);
}

static int vp8_need_keyframe(PayloadContext *vp8)
{
    return vp8->sequence_dirty || !vp8->sequence_ok;
}

RTPDynamicProtocolHandler ff_vp8_dynamic_handler = {
    .enc_name       = "VP8",
    .codec_type     = AVMEDIA_TYPE_VIDEO,
    .codec_id       = AV_CODEC_ID_VP8,
    .alloc          = vp8_new_context,
    .free           = vp8_free_context,
    .parse_packet   = vp8_handle_packet,
    .need_keyframe  = vp8_need_keyframe,
};