title: Conversion failed. 2 frames left in the queue on closing ffmpeg
body: <p>My simplified ffmpeg command (the longer one has over 300 files) is the following.</p>
  
  <pre><code>ffmpeg -i "v1.mp4" -i "v2.mp4" -i "v3.mp4"
      -filter_complex "[0:v:0][1:v:0][2:v:0]concat=n=3:v=1:a=0,fps=fps=30[cv1]; 
          [0:a:0][1:a:0][2:a:0]concat=n=3:v=0:a=1,asetpts=N/SR/TB[ca1]; 
          [cv1]setpts=0.25*PTS[v4]; 
          [ca1]atempo=4,asetpts=N/SR/TB[a4]" 
      -c:v h264_nvenc -map "[v4]" -map "[a4]" x4_output_0.mp4
  </code></pre>
  
  <p>The video encoding is working but then breaks and the output file seems to be truncated. The output files are nearly of the size as they should be but they can't be read.</p>
  
  <pre><code>Video encoding failed\r\n
  [aac @ 00000248a7856840] Qavg: 325.600\r\n
  [aac @ 00000248a7856840] 2 frames left in the queue on closing\r\n
  [aac @ 00000248a78595c0] Qavg: 236.279\r\n[aac @ 00000248a78595c0] 
  2 frames left in the queue on closing\r\n
  [aac @ 00000248a7855140] Qavg: 2729.299\r\n
  [aac @ 00000248a7855140] 2 frames left in the queue on closing\r\n
  [aac @ 00000248a785bec0] Qavg: 1158.664\r\n
  [aac @ 00000248a785bec0] 2 frames left in the queue on closing\r\n
  Conversion failed!\r\n")
  </code></pre>
  
  <ol>
  <li>Does the error have anything to do with the audio part of .mp4 since <code>aac @ ...</code>? </li>
  <li>What does the <code>Qavg</code> mean in the error message?</li>
  <li>What is the difference in the video stream between the <code>codec_time_base</code> and the <code>time_base</code> (see the differences in the video attributes frequencies below)?</li>
  </ol>
  
  <p>Below are the frequencies of the video attributes for all videos that have more than 1 distinct value. It's of the form <code>[(value, frequency), (value, frequency),...]</code>.</p>
  
  <pre><code>codec_time_base --- [('1/60', 384), ('1001/60000', 7), ('50/2997', 1)]
  has_b_frames --- [(0, 336), (2, 56)]
  level --- [(31, 336), (30, 56)]
  r_frame_rate --- [('30/1', 384), ('30000/1001', 7), ('2997/100', 1)]
  avg_frame_rate --- [('30/1', 384), ('30000/1001', 7), ('2997/100', 1)]
  time_base --- [('1/30', 383), ('1/30000', 7), ('1/2997', 1), ('1/15360', 1)]
  </code></pre>
  
  <p>The same for the audio attributes in all those video files.</p>
  
  <pre><code>codec_time_base --- [('1/48000', 386), ('1/44100', 6)]
  sample_rate --- [('48000', 386), ('44100', 6)]
  time_base --- [('1/48000', 386), ('1/44100', 6)]
  </code></pre>
  
  <ol start="4">
  <li>Is it possible that something is not right with some of the video files here that causes the breakdown of the encoding?</li>
  </ol>