ffmpeg 帧率问题分析-白红宇

ffmpeg 帧率问题分析

阅读量：198 次

发布时间：2019-02-28

本文共 1415 字，大约阅读时间需要 4 分钟。

static int process_input_packet(InputStream *ist, const AVPacket *pkt, int no_eof)

{

/* 数据不需要解码只需要复制 */

if (!ist->decoding_needed) {

ist->dts = ist->next_dts;

switch (ist->dec_ctx->codec_type) {

case AVMEDIA_TYPE_AUDIO:

ist->next_dts += ((int64_t)AV_TIME_BASE * ist->dec_ctx->frame_size) /

ist->dec_ctx->sample_rate;

break;

//这个case里面专门处理帧率的问题当选择-re选项时会进入pkt->duration中此处为40000 大概是40ms 也就是25帧

case AVMEDIA_TYPE_VIDEO:

if (ist->framerate.num) {

// TODO: Remove work-around for c99-to-c89 issue 7

AVRational time_base_q = AV_TIME_BASE_Q;

int64_t next_dts = av_rescale_q(ist->next_dts, time_base_q, av_inv_q(ist->framerate));

ist->next_dts = av_rescale_q(next_dts + 1, av_inv_q(ist->framerate), time_base_q);

} else if (pkt->duration) {

ist->next_dts += av_rescale_q(pkt->duration, ist->st->time_base, AV_TIME_BASE_Q);

} else if(ist->dec_ctx->framerate.num != 0) {

int ticks= av_stream_get_parser(ist->st) ? av_stream_get_parser(ist->st)->repeat_pict + 1 : ist->dec_ctx->ticks_per_frame;

ist->next_dts += ((int64_t)AV_TIME_BASE *

ist->dec_ctx->framerate.den * ticks) /

ist->dec_ctx->framerate.num / ist->dec_ctx->ticks_per_frame;

}

break;

}

ist->pts = ist->dts;

ist->next_pts = ist->next_dts;

}

for (i = 0; pkt && i < nb_output_streams; i++) {

OutputStream *ost = output_streams[i];

if (!check_output_constraints(ist, ost) || ost->encoding_needed)

continue;

do_streamcopy(ist, ost, pkt);

}

return !eof_reached;

}

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