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• Understanding PTS and DTS in video frames

  28 juin 2017, par theateist

  I had fps issues when transcoding from avi to mp4(x264). Eventually the problem was in PTS and DTS values, so lines 12-15 where added before av_interleaved_write_frame function :

  1.  AVFormatContext* outContainer = NULL;
  
  2.  avformat_alloc_output_context2(&outContainer, NULL, "mp4", "c:\\test.mp4";
  
  3.  AVCodec *encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
  
  4.  AVStream *outStream = avformat_new_stream(outContainer, encoder);
  
  5.  // outStream->codec initiation
  
  6.  // ...
  
  7.  avformat_write_header(outContainer, NULL);
  
  
  
  8.  // reading and decoding packet
  
  9.  // ...
  
  10. avcodec_encode_video2(outStream->codec, &encodedPacket, decodedFrame, &got_frame)
  
  11. 
  
  12. if (encodedPacket.pts != AV_NOPTS_VALUE)
  
  13.     encodedPacket.pts =  av_rescale_q(encodedPacket.pts, outStream->codec->time_base, outStream->time_base);
  
  14. if (encodedPacket.dts != AV_NOPTS_VALUE)
  
  15.     encodedPacket.dts = av_rescale_q(encodedPacket.dts, outStream->codec->time_base, outStream->time_base);
  
  16. 
  
  17. av_interleaved_write_frame(outContainer, &encodedPacket)

  After reading many posts I still do not understand :

  1. outStream->codec->time_base = 1/25 and outStream->time_base = 1/12800. The 1st one was set by me but I cannot figure out why and who set 12800 ? I noticed that before line (7) outStream->time_base = 1/90000 and right after it it changes to 1/12800, why ?
     When I transcode from avi to avi, meaning changing the line (2) to avformat_alloc_output_context2(&outContainer, NULL, "avi", "c:\\test.avi"; , so before and after line (7) outStream->time_base remains always 1/25 and not like in mp4 case, why ?
  2. What is the difference between time_base of outStream->codec and outStream ?
  3. To calc the pts av_rescale_q does : takes 2 time_base, multiplies their fractions in cross and then compute the pts. Why it does this in this way ? As I debugged, the encodedPacket.pts has value incremental by 1, so why changing it if it does has value ?
  4. At the beginning the dts value is -2 and after each rescaling it still has negative number, but despite this the video played correctly ! Shouldn’t it be positive ?

• Understanding PTS and DTS in video frames

  8 août 2015, par theateist

  I had fps issues when transcoding from avi to mp4(x264). Eventually the problem was in PTS and DTS values, so lines 12-15 where added before av_interleaved_write_frame function :

  1.  AVFormatContext* outContainer = NULL;
  
  2.  avformat_alloc_output_context2(&outContainer, NULL, "mp4", "c:\\test.mp4";
  
  3.  AVCodec *encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
  
  4.  AVStream *outStream = avformat_new_stream(outContainer, encoder);
  
  5.  // outStream->codec initiation
  
  6.  // ...
  
  7.  avformat_write_header(outContainer, NULL);
  
  
  
  8.  // reading and decoding packet
  
  9.  // ...
  
  10. avcodec_encode_video2(outStream->codec, &encodedPacket, decodedFrame, &got_frame)
  
  11. 
  
  12. if (encodedPacket.pts != AV_NOPTS_VALUE)
  
  13.     encodedPacket.pts =  av_rescale_q(encodedPacket.pts, outStream->codec->time_base, outStream->time_base);
  
  14. if (encodedPacket.dts != AV_NOPTS_VALUE)
  
  15.     encodedPacket.dts = av_rescale_q(encodedPacket.dts, outStream->codec->time_base, outStream->time_base);
  
  16. 
  
  17. av_interleaved_write_frame(outContainer, &encodedPacket)

  After reading many posts I still do not understand :

  1. outStream->codec->time_base = 1/25 and outStream->time_base = 1/12800. The 1st one was set by me but I cannot figure out why and who set 12800 ? I noticed that before line (7) outStream->time_base = 1/90000 and right after it it changes to 1/12800, why ?
     When I transcode from avi to avi, meaning changing the line (2) to avformat_alloc_output_context2(&outContainer, NULL, "avi", "c:\\test.avi"; , so before and after line (7) outStream->time_base remains always 1/25 and not like in mp4 case, why ?
  2. What is the difference between time_base of outStream->codec and outStream ?
  3. To calc the pts av_rescale_q does : takes 2 time_base, multiplies their fractions in cross and then compute the pts. Why it does this in this way ? As I debugged, the encodedPacket.pts has value incremental by 1, so why changing it if it does has value ?
  4. At the beginning the dts value is -2 and after each rescaling it still has negative number, but despite this the video played correctly ! Shouldn’t it be positive ?

• Terminate ffmpeg.exe loop

  5 mars 2019, par jinaho

  Getting a thumbnail from a RTSP source results in infinit output from ffmpeg without exiting which makes the batch script not resume.

  It is basically only one line that calls the ffmpeg process like this (example) :

  ffmpeg -i rtsp://192.168.1.89:554/11 -f image2 -r 1 thumb%03d.jpg

  The input is user generated and for some ffmpeg is not returning a thumbnail but a warning message :

  Could not find codec parameters for stream 0 (Video: h264, 1 reference frame, none(left), 1280x720, 1/180000): unspecified pixel format

  After that instead of quiting and let the batch script resume, ffmpeg outputs :

  Press [q] to stop, [?] for help
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A
  
  frame=    0 fps=0.0 q=0.0 size=N/A time=-577014:32:22.77 bitrate=N/A speed=N/A

  This goes on forever meaning that the batch script does not resume. Manual invertention is required which is not intended.
  I am looking for a way to tell the script that ffmpeg has a hanging condition and make the script quit ffmpeg so it can resume.