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POChoppy sound when using ffmpeg
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  1. POChoppy sound when using ffmpeg
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    copied!<p>I suffered some choppy audio when i try to capture audio from a live stream. Another essential problem which could explain the problem is that the Wav file created is twice longer than the capture time.</p> <p>The audio is perfect when i play the avs input file with ffplay, so the avs is ok, the problem is after whether in the capture or in the Wav writing.</p> <p>To capture :</p> <pre><code>av_read_frame(pFormatCtx, &amp;packet) if(packet.stream_index == mAudioStream) { int buff_size = sizeof(mAudioBuffer); std::cout &lt;&lt; "Buff_size " &lt;&lt; buff_size &lt;&lt; std::endl; len = avcodec_decode_audio3(pAudioCodecCtx,(int16_t*)mAudioBuffer, &amp;buff_size,&amp;packet); if(len &lt; 0){ qDebug("Extractor - Audio isEnd = -1;"); mAudioBufferSize = 0; isEnd = ERROR_; return isEnd; } // Set packet result type mFrameType = AUDIO_PKT; mAudioBufferSize = buff_size; //store audio synchronization informations: if(packet.pts != AV_NOPTS_VALUE) { mAudioPts_ = av_q2d(pFormatCtx-&gt;streams[mAudioStream]-&gt;time_base); mAudioPts_ *= packet.pts; } } // store a copy of current audio frame in _frame _frame.audioFrame = new decoded_frame_t::audio_frame_t(); _frame.audioFrame-&gt;sampleRate = mediaInfos.audioSampleRate; _frame.audioFrame-&gt;sampleSize = mediaInfos.audioSampleSize; _frame.audioFrame-&gt;nbChannels = mediaInfos.audioNbChannels; _frame.audioFrame-&gt;nbSamples = mAudioBufferSize / ((mediaInfos.audioSampleSize/8) * mediaInfos.audioNbChannels); _frame.audioFrame-&gt;buf.resize(mAudioBufferSize); memcpy(&amp;_frame.audioFrame-&gt;buf[0],mAudioBuffer,mAudioBufferSize); </code></pre> <p>Then i store in a Wav File using libsndfile :</p> <pre><code>SNDFILE* fd; SF_INFO sfInf; sfInf.frames = 0; sfInf.channels = p_capt-&gt;ui_nbChannels; sfInf.samplerate = p_capt-&gt;ui_sampleRate; sfInf.format = SF_FORMAT_WAV | SF_FORMAT_PCM_U8; sfInf.sections = 0; sfInf.seekable = 0; if (sf_format_check(&amp;sfInf) == FALSE) std::cout &lt;&lt; "Format parameter are uncorrect ! Exit saving !" &lt;&lt; std::endl; else { fd = sf_open(fileName.toStdString().c_str(), SFM_WRITE, &amp;sfInf); if (fd == NULL) { std::cout &lt;&lt; "Unable to open the file " &lt;&lt; fileName.toStdString() &lt;&lt; std::endl; return GRAB_ST_NOK; } //little trick because v_buf is a uint8_t vector sf_count_t l = sf_write_short(fd, (const short *)(&amp;(p_capt-&gt;v_buf[0])), p_capt-&gt;v_buf.size()/2); if (l != p_capt-&gt;v_buf.size()/2) { std::cout &lt;&lt; "sf_write didn't write the right amoung of bits " &lt;&lt; l &lt;&lt; " != " &lt;&lt; p_capt-&gt;v_buf.size()/2 &lt;&lt; std::endl; ret = GRAB_ST_NOK; } else { sf_write_sync(fd); sf_close(fd); ret = GRAB_ST_OK; } } </code></pre> <p>I hope it's understandable. Waiting for remarks.</p> <p>Kurt</p>
 

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