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https://gitee.com/openharmony/third_party_ffmpeg
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9200514ad8
Currently, AVStream contains an embedded AVCodecContext instance, which
is used by demuxers to export stream parameters to the caller and by
muxers to receive stream parameters from the caller. It is also used
internally as the codec context that is passed to parsers.
In addition, it is also widely used by the callers as the decoding (when
demuxer) or encoding (when muxing) context, though this has been
officially discouraged since Libav 11.
There are multiple important problems with this approach:
- the fields in AVCodecContext are in general one of
* stream parameters
* codec options
* codec state
However, it's not clear which ones are which. It is consequently
unclear which fields are a demuxer allowed to set or a muxer allowed to
read. This leads to erratic behaviour depending on whether decoding or
encoding is being performed or not (and whether it uses the AVStream
embedded codec context).
- various synchronization issues arising from the fact that the same
context is used by several different APIs (muxers/demuxers,
parsers, bitstream filters and encoders/decoders) simultaneously, with
there being no clear rules for who can modify what and the different
processes being typically delayed with respect to each other.
- avformat_find_stream_info() making it necessary to support opening
and closing a single codec context multiple times, thus
complicating the semantics of freeing various allocated objects in the
codec context.
Those problems are resolved by replacing the AVStream embedded codec
context with a newly added AVCodecParameters instance, which stores only
the stream parameters exported by the demuxers or read by the muxers.
146 lines
4.2 KiB
C
146 lines
4.2 KiB
C
/*
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* Copyright (C) 2008 Ramiro Polla
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*
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* This file is part of Libav.
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*
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* Libav 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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* Libav 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 Libav; 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 "libavcodec/bytestream.h"
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#include "avformat.h"
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#include "internal.h"
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#define HEADER_SIZE 24
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/*
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* Header structure:
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* uint16_t ss; // struct size
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* uint16_t width; // frame width
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* uint16_t height; // frame height
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* uint16_t ff; // keyframe + some other info(???)
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* uint32_t size; // size of data
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* uint32_t fourcc; // ML20
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* uint32_t u3; // ?
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* uint32_t ts; // time
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*/
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static int msnwc_tcp_probe(AVProbeData *p)
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{
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int i;
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for (i = 0; i + HEADER_SIZE <= p->buf_size; i++) {
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uint16_t width, height;
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uint32_t fourcc;
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const uint8_t *bytestream = p->buf + i;
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if (bytestream_get_le16(&bytestream) != HEADER_SIZE)
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continue;
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width = bytestream_get_le16(&bytestream);
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height = bytestream_get_le16(&bytestream);
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if (!(width == 320 &&
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height == 240) && !(width == 160 && height == 120))
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continue;
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bytestream += 2; // keyframe
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bytestream += 4; // size
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fourcc = bytestream_get_le32(&bytestream);
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if (fourcc != MKTAG('M', 'L', '2', '0'))
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continue;
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if (i) {
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if (i < 14) /* starts with SwitchBoard connection info */
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return AVPROBE_SCORE_MAX / 2;
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else /* starts in the middle of stream */
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return AVPROBE_SCORE_MAX / 3;
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} else {
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return AVPROBE_SCORE_MAX;
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}
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}
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return 0;
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}
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static int msnwc_tcp_read_header(AVFormatContext *ctx)
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{
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AVIOContext *pb = ctx->pb;
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AVCodecParameters *par;
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AVStream *st;
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st = avformat_new_stream(ctx, NULL);
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if (!st)
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return AVERROR(ENOMEM);
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par = st->codecpar;
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par->codec_type = AVMEDIA_TYPE_VIDEO;
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par->codec_id = AV_CODEC_ID_MIMIC;
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par->codec_tag = MKTAG('M', 'L', '2', '0');
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avpriv_set_pts_info(st, 32, 1, 1000);
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/* Some files start with "connected\r\n\r\n".
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* So skip until we find the first byte of struct size */
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while (avio_r8(pb) != HEADER_SIZE && !pb->eof_reached) ;
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if (pb->eof_reached) {
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av_log(ctx, AV_LOG_ERROR, "Could not find valid start.");
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return AVERROR_INVALIDDATA;
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}
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return 0;
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}
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static int msnwc_tcp_read_packet(AVFormatContext *ctx, AVPacket *pkt)
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{
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AVIOContext *pb = ctx->pb;
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uint16_t keyframe;
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uint32_t size, timestamp;
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int ret;
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avio_skip(pb, 1); /* one byte has been read ahead */
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avio_skip(pb, 2);
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avio_skip(pb, 2);
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keyframe = avio_rl16(pb);
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size = avio_rl32(pb);
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avio_skip(pb, 4);
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avio_skip(pb, 4);
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timestamp = avio_rl32(pb);
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if (!size)
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return AVERROR_INVALIDDATA;
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if ((ret = av_get_packet(pb, pkt, size)) < 0)
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return ret;
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avio_skip(pb, 1); /* Read ahead one byte of struct size like read_header */
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pkt->pts = timestamp;
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pkt->dts = timestamp;
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pkt->stream_index = 0;
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/* Some aMsn generated videos (or was it Mercury Messenger?) don't set
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* this bit and rely on the codec to get keyframe information */
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if (keyframe & 1)
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pkt->flags |= AV_PKT_FLAG_KEY;
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return HEADER_SIZE + size;
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}
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AVInputFormat ff_msnwc_tcp_demuxer = {
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.name = "msnwctcp",
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.long_name = NULL_IF_CONFIG_SMALL("MSN TCP Webcam stream"),
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.read_probe = msnwc_tcp_probe,
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.read_header = msnwc_tcp_read_header,
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.read_packet = msnwc_tcp_read_packet,
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};
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