https://blog.csdn.net/wishfly/article/details/51783809

av_write_frame 与 av_interleaved_write_frame

2016年06月29日 16:14:44 Tianyu-liu 阅读数：2563

1、函数介绍

av_interleaved_write_frame函数介绍：

[cpp] view plain copy

/**
* Write a packet to an output media file ensuring correct interleaving.
*
* This function will buffer the packets internally as needed to make sure the
* packets in the output file are properly interleaved in the order of
* increasing dts. Callers doing their own interleaving should call
* av_write_frame() instead of this function.
*
* @param s media file handle
* @param pkt The packet containing the data to be written.
*
* If the packet is reference-counted, this function will take
* ownership of this reference and unreference it later when it sees
* fit.
* The caller must not access the data through this reference after
* this function returns. If the packet is not reference-counted,
* libavformat will make a copy.
*
* This parameter can be NULL (at any time, not just at the end), to
* flush the interleaving queues.
*
* Packet's @ref AVPacket.stream_index "stream_index" field must be
* set to the index of the corresponding stream in @ref
* AVFormatContext.streams "s->streams". It is very strongly
* recommended that timing information (@ref AVPacket.pts "pts", @ref
* AVPacket.dts "dts", @ref AVPacket.duration "duration") is set to
* correct values.
*
* @return 0 on success, a negative AVERROR on error. Libavformat will always
* take care of freeing the packet, even if this function fails.
*
* @see av_write_frame(), AVFormatContext.max_interleave_delta
*/
int av_interleaved_write_frame(AVFormatContext *s, AVPacket *pkt);

av_write_frame函数介绍：

[cpp] view plain copy

/**
* Write a packet to an output media file.
*
* This function passes the packet directly to the muxer, without any buffering
* or reordering. The caller is responsible for correctly interleaving the
* packets if the format requires it. Callers that want libavformat to handle
* the interleaving should call av_interleaved_write_frame() instead of this
* function.
*
* @param s media file handle
* @param pkt The packet containing the data to be written. Note that unlike
* av_interleaved_write_frame(), this function does not take
* ownership of the packet passed to it (though some muxers may make
* an internal reference to the input packet).
*
* This parameter can be NULL (at any time, not just at the end), in
* order to immediately flush data buffered within the muxer, for
* muxers that buffer up data internally before writing it to the
* output.
*
* Packet's @ref AVPacket.stream_index "stream_index" field must be
* set to the index of the corresponding stream in @ref
* AVFormatContext.streams "s->streams". It is very strongly
* recommended that timing information (@ref AVPacket.pts "pts", @ref
* AVPacket.dts "dts", @ref AVPacket.duration "duration") is set to
* correct values.
* @return < 0 on error, = 0 if OK, 1 if flushed and there is no more data to flush
*
* @see av_interleaved_write_frame()
*/
int av_write_frame(AVFormatContext *s, AVPacket *pkt);

2、函数调用图

av_interleaved_write_frame函数调用图：

av_write_frame函数调用图：

3、函数代码

av_interleaved_write_frame函数代码：

[cpp] view plain copy

int av_interleaved_write_frame(AVFormatContext *s, AVPacket *pkt)
{
int ret, flush = 0;
//检查pkt是否合法
ret = check_packet(s, pkt);
if (ret < 0)
goto fail;
if (pkt) {
AVStream *st = s->streams[pkt->stream_index];
av_dlog(s, "av_interleaved_write_frame size:%d dts:%s pts:%s\n",
pkt->size, av_ts2str(pkt->dts), av_ts2str(pkt->pts));
if ((ret = compute_pkt_fields2(s, st, pkt)) < 0 && !(s->oformat->flags & AVFMT_NOTIMESTAMPS))//计算和检查pts、dts、duration
goto fail;
if (pkt->dts == AV_NOPTS_VALUE && !(s->oformat->flags & AVFMT_NOTIMESTAMPS)) {
ret = AVERROR(EINVAL);
goto fail;
}
} else {
av_dlog(s, "av_interleaved_write_frame FLUSH\n");
flush = 1;
}
for (;; ) {
AVPacket opkt;
int ret = interleave_packet(s, &opkt, pkt, flush);
if (pkt) {
memset(pkt, 0, sizeof(*pkt));
av_init_packet(pkt);
pkt = NULL;
}
if (ret <= 0) //FIXME cleanup needed for ret<0 ?
return ret;
ret = write_packet(s, &opkt);
if (ret >= 0)
s->streams[opkt.stream_index]->nb_frames++;
av_free_packet(&opkt);
if (ret < 0)
return ret;
if(s->pb && s->pb->error)
return s->pb->error;
}
fail:
av_packet_unref(pkt);
return ret;
}

av_write_frame函数代码：

[cpp] view plain copy

int av_write_frame(AVFormatContext *s, AVPacket *pkt)
{
int ret;
ret = check_packet(s, pkt);
if (ret < 0)
return ret;
if (!pkt) {
if (s->oformat->flags & AVFMT_ALLOW_FLUSH) {
ret = s->oformat->write_packet(s, NULL);
if (s->flush_packets && s->pb && s->pb->error >= 0 && s->flags & AVFMT_FLAG_FLUSH_PACKETS)
avio_flush(s->pb);
if (ret >= 0 && s->pb && s->pb->error < 0)
ret = s->pb->error;
return ret;
}
return 1;
}
ret = compute_pkt_fields2(s, s->streams[pkt->stream_index], pkt);
if (ret < 0 && !(s->oformat->flags & AVFMT_NOTIMESTAMPS))
return ret;
ret = write_packet(s, pkt);
if (ret >= 0 && s->pb && s->pb->error < 0)
ret = s->pb->error;
if (ret >= 0)
s->streams[pkt->stream_index]->nb_frames++;
return ret;
}

4、解释

可以看出2个函数的区别在于av_interleaved_write_frame调用了interleave_packet，而av_write_frame没有调用，看看interleave_packet的代码：

[cpp] view plain copy

static int interleave_packet(AVFormatContext *s, AVPacket *out, AVPacket *in, int flush)
{
if (s->oformat->interleave_packet) {
int ret = s->oformat->interleave_packet(s, out, in, flush);
if (in)
av_free_packet(in);
return ret;
} else
return ff_interleave_packet_per_dts(s, out, in, flush);
}

代码非常简单，如果AVOutputFormat有interleave_packet函数指针，则调用，如果没有则调用ff_interleave_packet_per_dts，看看ff_interleave_packet_per_dts的代码：
[cpp] view plain copy

int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
AVPacket *pkt, int flush)
{
AVPacketList *pktl;
int stream_count = 0;
int noninterleaved_count = 0;
int i, ret;
if (pkt) {//把pkt加入到AVPacketList中去
if ((ret = ff_interleave_add_packet(s, pkt, interleave_compare_dts)) < 0)
return ret;
}
for (i = 0; i < s->nb_streams; i++) {
if (s->streams[i]->last_in_packet_buffer) {
++stream_count;
} else if (s->streams[i]->codec->codec_type != AVMEDIA_TYPE_ATTACHMENT &&
s->streams[i]->codec->codec_id != AV_CODEC_ID_VP8 &&
s->streams[i]->codec->codec_id != AV_CODEC_ID_VP9) {
++noninterleaved_count;
}
}
if (s->internal->nb_interleaved_streams == stream_count)
flush = 1;
if (s->max_interleave_delta > 0 &&
s->internal->packet_buffer &&
!flush &&
s->internal->nb_interleaved_streams == stream_count+noninterleaved_count
) {
AVPacket *top_pkt = &s->internal->packet_buffer->pkt;
int64_t delta_dts = INT64_MIN;
int64_t top_dts = av_rescale_q(top_pkt->dts,
s->streams[top_pkt->stream_index]->time_base,
AV_TIME_BASE_Q);
for (i = 0; i < s->nb_streams; i++) {
int64_t last_dts;
const AVPacketList *last = s->streams[i]->last_in_packet_buffer;
if (!last)
continue;
last_dts = av_rescale_q(last->pkt.dts,
s->streams[i]->time_base,
AV_TIME_BASE_Q);
delta_dts = FFMAX(delta_dts, last_dts - top_dts);
}
if (delta_dts > s->max_interleave_delta) {
av_log(s, AV_LOG_DEBUG,
"Delay between the first packet and last packet in the "
"muxing queue is %"PRId64" > %"PRId64": forcing output\n",
delta_dts, s->max_interleave_delta);
flush = 1;
}
}
if (stream_count && flush) {
AVStream *st;
pktl = s->internal->packet_buffer;
*out = pktl->pkt;
st = s->streams[out->stream_index];
s->internal->packet_buffer = pktl->next;
if (!s->internal->packet_buffer)
s->internal->packet_buffer_end = NULL;
if (st->last_in_packet_buffer == pktl)
st->last_in_packet_buffer = NULL;
av_freep(&pktl);
return 1;
} else {
av_init_packet(out);
return 0;
}
}

从代码中看到，函数ff_interleave_packet_per_dts调用ff_interleave_add_packet把pkt加入缓存，然后再从缓存中取出第一个pkt返回。
看看ff_interleave_add_packet的代码：[cpp] view plain copy

int ff_interleave_add_packet(AVFormatContext *s, AVPacket *pkt,
int (*compare)(AVFormatContext *, AVPacket *, AVPacket *))
{
int ret;
AVPacketList **next_point, *this_pktl;
AVStream *st = s->streams[pkt->stream_index];
int chunked = s->max_chunk_size || s->max_chunk_duration;
this_pktl = av_mallocz(sizeof(AVPacketList));
if (!this_pktl)
return AVERROR(ENOMEM);
this_pktl->pkt = *pkt;
#if FF_API_DESTRUCT_PACKET
FF_DISABLE_DEPRECATION_WARNINGS
pkt->destruct = NULL; // do not free original but only the copy
FF_ENABLE_DEPRECATION_WARNINGS
#endif
pkt->buf = NULL;
pkt->side_data = NULL;
pkt->side_data_elems = 0;
if ((pkt->flags & AV_PKT_FLAG_UNCODED_FRAME)) {
av_assert0(pkt->size == UNCODED_FRAME_PACKET_SIZE);
av_assert0(((AVFrame *)pkt->data)->buf);
} else {
// Duplicate the packet if it uses non-allocated memory
if ((ret = av_dup_packet(&this_pktl->pkt)) < 0) {
av_free(this_pktl);
return ret;
}
}
if (s->streams[pkt->stream_index]->last_in_packet_buffer) {
next_point = &(st->last_in_packet_buffer->next);
} else {
next_point = &s->internal->packet_buffer;
}
if (chunked) {
uint64_t max= av_rescale_q_rnd(s->max_chunk_duration, AV_TIME_BASE_Q, st->time_base, AV_ROUND_UP);
st->interleaver_chunk_size += pkt->size;
st->interleaver_chunk_duration += pkt->duration;
if ( (s->max_chunk_size && st->interleaver_chunk_size > s->max_chunk_size)
|| (max && st->interleaver_chunk_duration > max)) {
st->interleaver_chunk_size = 0;
this_pktl->pkt.flags |= CHUNK_START;
if (max && st->interleaver_chunk_duration > max) {
int64_t syncoffset = (st->codec->codec_type == AVMEDIA_TYPE_VIDEO)*max/2;
int64_t syncto = av_rescale(pkt->dts + syncoffset, 1, max)*max - syncoffset;
st->interleaver_chunk_duration += (pkt->dts - syncto)/8 - max;
} else
st->interleaver_chunk_duration = 0;
}
}
if (*next_point) {
if (chunked && !(this_pktl->pkt.flags & CHUNK_START))
goto next_non_null;
if (compare(s, &s->internal->packet_buffer_end->pkt, pkt)) {
while ( *next_point
&& ((chunked && !((*next_point)->pkt.flags&CHUNK_START))
|| !compare(s, &(*next_point)->pkt, pkt)))
next_point = &(*next_point)->next;
if (*next_point)
goto next_non_null;
} else {
next_point = &(s->internal->packet_buffer_end->next);
}
}
av_assert1(!*next_point);
s->internal->packet_buffer_end = this_pktl;
next_non_null:
this_pktl->next = *next_point;
s->streams[pkt->stream_index]->last_in_packet_buffer =
*next_point = this_pktl;
return 0;
}

代码中可以看到，函数ff_interleave_add_packet把pkt经过排序（如果缓存中有pkt的话）加入到缓存中，这个排序是根据ff_interleave_packet_per_dts函数传入的compare（其实就是函数interleave_compare_dts）指针做的，来看看interleave_compare_dts函数的代码：[cpp] view plain copy

static int interleave_compare_dts(AVFormatContext *s, AVPacket *next,
AVPacket *pkt)
{
AVStream *st = s->streams[pkt->stream_index];
AVStream *st2 = s->streams[next->stream_index];
int comp = av_compare_ts(next->dts, st2->time_base, pkt->dts,
st->time_base);
if (s->audio_preload && ((st->codec->codec_type == AVMEDIA_TYPE_AUDIO) != (st2->codec->codec_type == AVMEDIA_TYPE_AUDIO))) {
int64_t ts = av_rescale_q(pkt ->dts, st ->time_base, AV_TIME_BASE_Q) - s->audio_preload*(st ->codec->codec_type == AVMEDIA_TYPE_AUDIO);
int64_t ts2= av_rescale_q(next->dts, st2->time_base, AV_TIME_BASE_Q) - s->audio_preload*(st2->codec->codec_type == AVMEDIA_TYPE_AUDIO);
if (ts == ts2) {
ts= ( pkt ->dts* st->time_base.num*AV_TIME_BASE - s->audio_preload*(int64_t)(st ->codec->codec_type == AVMEDIA_TYPE_AUDIO)* st->time_base.den)*st2->time_base.den
-( next->dts*st2->time_base.num*AV_TIME_BASE - s->audio_preload*(int64_t)(st2->codec->codec_type == AVMEDIA_TYPE_AUDIO)*st2->time_base.den)* st->time_base.den;
ts2=0;
}
comp= (ts>ts2) - (ts<ts2);
}
if (comp == 0)
return pkt->stream_index < next->stream_index;
return comp > 0;
}

从代码中可以看到interleave_compare_dts函数其实就是在比较传入的2个pkt的dts值，其实就是比那个的dts更早，如果有音频还有audio_preload（音频预加载时间）的话，还需要把音频包的预加载时间算进去。

好了，现在整体逻辑就清晰了，得出的结论是：在有多个流的情况下要用av_interleaved_write_frame，只有单一流2个函数都可以用。

http://blog.csdn.net/dancing_night/article/details/46469865