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<meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">When open input decoder, there is an option that set how many frame will be buffer on decoder side: <div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class=""><div class="">for (i = 0; i < ifmt_ctx->nb_streams; i++) {</div></div><div class=""><div class=""> AVStream *stream;</div></div><div class=""><div class=""> AVCodecContext *codec_ctx;</div></div><div class=""><div class=""> stream = ifmt_ctx->streams[i];</div></div><div class=""><div class=""> codec_ctx = stream->codec;</div></div><div class=""><div class=""> codec_ctx->delay = 5;</div></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>…..</div><div class=""><br class=""></div><div class=""><br class=""></div></blockquote><div class="">Notice option delay = 5, with that option set, there’s always 5 frames buffered even when you’ve finished decode/encode steps (at least with h264 decoder)</div><div class="">To disable delay, set coder_ctx->delay = 0 (correct me if I am wrong) or you have to do something like this:</div><div class=""><br class=""></div><div class="">1. set a counting variable to count how many frame was left on decoder: </div><div class="">int skip_frame = 0; </div><div class=""><br class=""></div><div class="">2. Whenever decoder fail to produce frame when decoding avpacket, ++ skip_frame: </div><div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class="">if (!got_frame): ++ skip_frame; </div></blockquote><div class=""><br class=""></div><div class="">3. When everything is finished, do something like this: </div><div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class=""><div class=""> for (int i = skip_frame; i > 0; i--) {</div></div><div class=""><div class=""> stream_index = packet.stream_index;</div></div><div class=""><div class=""> type = ifmt_ctx->streams[packet.stream_index]->codec->codec_type;</div></div><div class=""><div class=""> if (type == AVMEDIA_TYPE_VIDEO) {</div></div><div class=""><div class=""> frame = av_frame_alloc();</div></div><div class=""><div class=""> ret = avcodec_decode_video2(ifmt_ctx->streams[stream_index]->codec</div></div><div class=""><div class=""> , frame, &got_frame, &packet);</div></div><div class=""><div class=""> if (got_frame) {</div></div><div class=""><div class=""> frame->pts = av_frame_get_best_effort_timestamp(frame);</div></div><div class=""><div class=""> ret = filter_encode_write_frame(frame, stream_index);</div></div><div class=""><div class=""> av_frame_free(&frame);</div></div><div class=""><div class=""> if (ret < 0)</div></div><div class=""><div class=""> goto end;</div></div><div class=""><div class=""> }</div></div><div class=""><div class=""> }</div></div><div class=""><div class=""> }</div></div></blockquote><div class=""><br class=""></div><div class=""><br class=""></div><div class="">That’s what I figured out after weeks working with libavcodec. </div><div class=""><br class=""></div><div class="">Hope this help.</div><div class=""><br class=""></div><div class="">--</div><br class=""><div class=""><div apple-content-edited="true" class="">
<div class="">Hung Nguyen</div><div class=""><a href="mailto:hungnv@opensource.com" class="">hungnv@opensource.com</a>.vn</div><br class="Apple-interchange-newline">
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<br class=""><div><blockquote type="cite" class=""><div class="">On Dec 5, 2014, at 5:12 AM, Hendrik Leppkes <<a href="mailto:h.leppkes@gmail.com" class="">h.leppkes@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><br class=""><div class="gmail_extra"><br class=""><div class="gmail_quote">On Thu, Dec 4, 2014 at 2:31 PM, Alina lifshits <span dir="ltr" class=""><<a href="mailto:alina@vicon.co.il" target="_blank" class="">alina@vicon.co.il</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple" class=""><div class=""><p class="MsoNormal">Hello,<u class=""></u><u class=""></u></p><p class="MsoNormal"><u class=""></u> <u class=""></u></p><p class="MsoNormal">I am using avcodec decoder to decode h264 stream. I noticed that the decoder buffers a few first frames before returning a decoded picture. <u class=""></u><u class=""></u></p><p class="MsoNormal">The stream is from a live source and does not contains B frames. Is there a way to tell the decoder not to buffer frames, or maybe to buffer just 1 or 2 at most?<u class=""></u><u class=""></u></p><p class="MsoNormal">Since I am working with a live video, it very important for me to keep small latency.<u class=""></u><u class=""></u></p><p class="MsoNormal"><u class=""></u> <u class=""></u></p><p class="MsoNormal"><br class=""></p></div></div></blockquote><div class=""><br class=""></div><div class="">To minimize latency, make sure you turn off frame-threaded decoding. You can still use slice-threading (if your video has slices), but frame-threading has an inherent delay.</div><div class="">Additionally, there is a flag to force low delay decoding, but I'm not certain it work for H.264. You could look into that.</div><div class=""><br class=""></div><div class="">- Hendrik</div></div></div></div>
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