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  • Different PTS values in ffmpeg and MP4 CTS values obtained using ctts and stts

    26 septembre 2023, par userDtrm

    I have been studying PTS values in .mp4 media files. PTS for video stream can be extracted from ffmpeg CLI using

    


    

    ffmpeg -hide_banner -i  -vf "showinfo" -f null -



    


    For a sample .mp4 I have downloaded from the internet shows the following output.

    


    

    Press [q] to stop, [?] for help
    [Parsed_showinfo_0 @ 0x3741c00] config in time_base : 1/30, frame_rate : 30/1
    [Parsed_showinfo_0 @ 0x3741c00] config out time_base : 0/0, frame_rate : 0/0
    [Parsed_showinfo_0 @ 0x3741c00] n :   0 pts :      0 pts_time:0       pos :    58852 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:1 type:I checksum:49058BA3 plane_checksum :[E852D7DE 07E2B7D4 EA12FBD3] mean :[75 123 124] stdev :[52.7 4.8 11.7]
    [Parsed_showinfo_0 @ 0x3741c00]   side data - User Data Unregistered :
    [Parsed_showinfo_0 @ 0x3741c00] UUID=dc45e9bd-e6d9-48b7-962c-d820d923eeef
    [Parsed_showinfo_0 @ 0x3741c00] User Data=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
    [Parsed_showinfo_0 @ 0x3741c00] 
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    Output #0, null, to 'pipe :' :
      Metadata :
        major_brand : mp42
        minor_version : 0
        compatible_brands : mp42mp41isomavc1
        encoder : Lavf59.27.100
      Stream #0:0(und) : Video : wrapped_avframe, yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 30 fps, 30 tbn (default)
        Metadata :
          creation_time : 2018-01-23T22:02:00.000000Z
          handler_name : L-SMASH Video Handler
          vendor_id : [0][0][0][0]
          encoder : Lavc59.37.100 wrapped_avframe
      Stream #0:1(und) : Audio : pcm_s16le, 48000 Hz, mono, s16, 768 kb/s (default)
        Metadata :
          creation_time : 2018-01-23T22:02:00.000000Z
          handler_name : L-SMASH Audio Handler
          vendor_id : [0][0][0][0]
          encoder : Lavc59.37.100 pcm_s16le
    [Parsed_showinfo_0 @ 0x3741c00] n :   1 pts :      1 pts_time:0.0333333 pos :   149037 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:2005D769 plane_checksum :[92BD4F7B 3501F48D 0CAA9352] mean :[75 124 124] stdev :[52.5 4.7 11.7]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   2 pts :      2 pts_time:0.0666667 pos :   139805 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:09AFB702 plane_checksum :[3E62184D 9D0A0753 8BF09762] mean :[75 124 124] stdev :[52.4 4.6 11.5]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   3 pts :      3 pts_time:0.1     pos :   157017 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:99F05FA9 plane_checksum :[FFA84276 7A3D6D59 0290AFCB] mean :[75 124 124] stdev :[52.2 4.5 11.3]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   4 pts :      4 pts_time:0.133333 pos :   117259 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:P checksum:00935CD8 plane_checksum :[F81E097E 5F17005D B01452FD] mean :[74 124 124] stdev :[52.2 4.5 11.3]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   5 pts :      5 pts_time:0.166667 pos :   197428 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:30E77B4C plane_checksum :[393DAA75 DFA88599 E2164B2F] mean :[74 124 125] stdev :[52.3 4.4 11.0]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   6 pts :      6 pts_time:0.2     pos :   187073 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:BD5C25BC plane_checksum :[CC66DD70 F4ACA5DB 955DA253] mean :[75 124 125] stdev :[52.2 4.4 10.8]



    


    As seen above, the output shows a starting PTS of 0 for 1st frame. However, I was looking at ctts, and stts entries in the MP4 headers with the help of ParseTimingInfoInMp4.py. This shows a different PTS (e.g., 0.0667s) for the 1st frame as seen below.

    


    

    ftyp    size              32
    mvhd    size             108
    iods    size              42
    tkhd    size              92
    edts    size              36
    mdhd    size              32
    Trak type :  b'vide'
    Video Trak Number 0 found
    video track timescale is 30
    mdhd    size              32
    hdlr    size              54
    vmhd    size              20
    dinf    size              36
    stsd    size             195
    stts size  2944  ctts size  2944
    0    dts = 0.0000 s,    pts = 0.0667 s,    diff in ms    66.67
    1    dts = 0.0333 s,    pts = 0.2000 s,    diff in ms    166.67
    2    dts = 0.0667 s,    pts = 0.1333 s,    diff in ms    66.67
    3    dts = 0.1000 s,    pts = 0.1000 s,    diff in ms    0.00
    4    dts = 0.1333 s,    pts = 0.1667 s,    diff in ms    33.33
    5    dts = 0.1667 s,    pts = 0.3333 s,    diff in ms    166.67
    6    dts = 0.2000 s,    pts = 0.2667 s,    diff in ms    66.67
    7    dts = 0.2333 s,    pts = 0.2333 s,    diff in ms    0.00
    8    dts = 0.2667 s,    pts = 0.3000 s,    diff in ms    33.33
    9    dts = 0.3000 s,    pts = 0.4333 s,    diff in ms    133.33
    10    dts = 0.3333 s,    pts = 0.3667 s,    diff in ms    33.33



    


    MP4Analyser shows the following entries for stss, ctts, and edts-> for video track.
stss entries for video track
ctts entries for video track
edts - width='300' height='136' /> elst entry for video track

    


    The sample file I have been using can be found in Sample mp4.

    


    Can someone please help me to understand

    


      

    1. why the PTS values shown in ffmpeg are different from PTS derived from stss and ctts ?

      2. 


    2. What is the correct process in deriving PTS from stts, ctts and edts entries in MP4 header ?

      3. 


    


  • Different PTS values in ffmpeg and MP4 CTS values obtained using ctts and stss

    25 septembre 2023, par userDtrm

    I have been studying PTS values in .mp4 media files. PTS for video stream can be extracted from ffmpeg CLI using

    


    

    ffmpeg -hide_banner -i  -vf "showinfo" -f null -



    


    For a sample .mp4 I have downloaded from the internet shows the following output.

    


    

    Press [q] to stop, [?] for help
    [Parsed_showinfo_0 @ 0x3741c00] config in time_base : 1/30, frame_rate : 30/1
    [Parsed_showinfo_0 @ 0x3741c00] config out time_base : 0/0, frame_rate : 0/0
    [Parsed_showinfo_0 @ 0x3741c00] n :   0 pts :      0 pts_time:0       pos :    58852 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:1 type:I checksum:49058BA3 plane_checksum :[E852D7DE 07E2B7D4 EA12FBD3] mean :[75 123 124] stdev :[52.7 4.8 11.7]
    [Parsed_showinfo_0 @ 0x3741c00]   side data - User Data Unregistered :
    [Parsed_showinfo_0 @ 0x3741c00] UUID=dc45e9bd-e6d9-48b7-962c-d820d923eeef
    [Parsed_showinfo_0 @ 0x3741c00] User Data=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
    [Parsed_showinfo_0 @ 0x3741c00] 
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    Output #0, null, to 'pipe :' :
      Metadata :
        major_brand : mp42
        minor_version : 0
        compatible_brands : mp42mp41isomavc1
        encoder : Lavf59.27.100
      Stream #0:0(und) : Video : wrapped_avframe, yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 30 fps, 30 tbn (default)
        Metadata :
          creation_time : 2018-01-23T22:02:00.000000Z
          handler_name : L-SMASH Video Handler
          vendor_id : [0][0][0][0]
          encoder : Lavc59.37.100 wrapped_avframe
      Stream #0:1(und) : Audio : pcm_s16le, 48000 Hz, mono, s16, 768 kb/s (default)
        Metadata :
          creation_time : 2018-01-23T22:02:00.000000Z
          handler_name : L-SMASH Audio Handler
          vendor_id : [0][0][0][0]
          encoder : Lavc59.37.100 pcm_s16le
    [Parsed_showinfo_0 @ 0x3741c00] n :   1 pts :      1 pts_time:0.0333333 pos :   149037 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:2005D769 plane_checksum :[92BD4F7B 3501F48D 0CAA9352] mean :[75 124 124] stdev :[52.5 4.7 11.7]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   2 pts :      2 pts_time:0.0666667 pos :   139805 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:09AFB702 plane_checksum :[3E62184D 9D0A0753 8BF09762] mean :[75 124 124] stdev :[52.4 4.6 11.5]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   3 pts :      3 pts_time:0.1     pos :   157017 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:99F05FA9 plane_checksum :[FFA84276 7A3D6D59 0290AFCB] mean :[75 124 124] stdev :[52.2 4.5 11.3]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   4 pts :      4 pts_time:0.133333 pos :   117259 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:P checksum:00935CD8 plane_checksum :[F81E097E 5F17005D B01452FD] mean :[74 124 124] stdev :[52.2 4.5 11.3]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   5 pts :      5 pts_time:0.166667 pos :   197428 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:30E77B4C plane_checksum :[393DAA75 DFA88599 E2164B2F] mean :[74 124 125] stdev :[52.3 4.4 11.0]
    [Parsed_showinfo_0 @ 0x3741c00] color_range:tv color_space:bt709 color_primaries:bt709 color_trc:bt709
    [Parsed_showinfo_0 @ 0x3741c00] n :   6 pts :      6 pts_time:0.2     pos :   187073 fmt:yuv420p sar:1/1 s:1920x1080 i:P iskey:0 type:B checksum:BD5C25BC plane_checksum :[CC66DD70 F4ACA5DB 955DA253] mean :[75 124 125] stdev :[52.2 4.4 10.8]



    


    As seen above, the output shows a starting PTS of 0 for 1st frame. However, I was looking at ctts, and stss entries in the MP4 headers with the help of ParseTimingInfoInMp4.py. This shows a different PTS (e.g., 0.0667s) for the 1st frame as seen below.

    


    

    ftyp    size              32
    mvhd    size             108
    iods    size              42
    tkhd    size              92
    edts    size              36
    mdhd    size              32
    Trak type :  b'vide'
    Video Trak Number 0 found
    video track timescale is 30
    mdhd    size              32
    hdlr    size              54
    vmhd    size              20
    dinf    size              36
    stsd    size             195
    stts size  2944  ctts size  2944
    0    dts = 0.0000 s,    pts = 0.0667 s,    diff in ms    66.67
    1    dts = 0.0333 s,    pts = 0.2000 s,    diff in ms    166.67
    2    dts = 0.0667 s,    pts = 0.1333 s,    diff in ms    66.67
    3    dts = 0.1000 s,    pts = 0.1000 s,    diff in ms    0.00
    4    dts = 0.1333 s,    pts = 0.1667 s,    diff in ms    33.33
    5    dts = 0.1667 s,    pts = 0.3333 s,    diff in ms    166.67
    6    dts = 0.2000 s,    pts = 0.2667 s,    diff in ms    66.67
    7    dts = 0.2333 s,    pts = 0.2333 s,    diff in ms    0.00
    8    dts = 0.2667 s,    pts = 0.3000 s,    diff in ms    33.33
    9    dts = 0.3000 s,    pts = 0.4333 s,    diff in ms    133.33
    10    dts = 0.3333 s,    pts = 0.3667 s,    diff in ms    33.33



    


    MP4Analyser shows the following entries for stss, ctts, and edts-> for video track.
stss entries for video track
ctts entries for video track
edts - width='300' height='136' /> elst entry for video track

    


    The sample file I have been using can be found in Sample mp4.

    


    Can someone please help me to understand

    


      

    1. why the PTS values shown in ffmpeg are different from PTS derived from stss and ctts ?

      2. 


    2. What is the correct process in deriving PTS from stss, ctts and edts entries in MP4 header ?

      3. 


    


  • OpenCV encoding to H264

    29 mars 2018, par Yost777

    I want to encode images to H264 video in OpenCV.

    As part of my software for image tracking, I’m using VideoWriter in OpenCV 3.4 (64-bit) with Visual Studio 2017 C++. I use ffmpeg for manual encoding, and as it comes with OpenCV I assume this is the best option. My version of OpenCV indicates it has been compiled with ffmpeg, and I can verify it loads the opencv_ffmpeg340_64.dll.

    Decoding H264 (AVC1) is absolutely fine, including when specifically using the ffmpeg API. But encoding anything other than MJPG or raw images doesn’t work :
    VideoWriter.Open() mostly returns false, for some cases it only writes an empty or small header but won’t write frames. I’ve tried not only the ffmpeg API, but also any available API. Redirecting console/debug output to intermediate window in VC doesn’t give any messages from OpenCV or ffmpeg.

    There are numerous posts on previous versions of OpenCV using FFmpeg, including (Cisco) OpenH264 library and difficulties using this. I’ve tried many options, installing codecs pack including H264, ffmpeg static version, Cisco openH264 library, setting paths etc and even tried the low level ffmpeg library functions such as cvCreateVideoWriter exposed in OpenCV, and using different video containers (AVI, MPG, MP4) as well as fourcc strings.

    I can’t believe in 2018 the great OpenCV with FFmpeg support is unable to encode anything but arcane MJPG or raw images. If it uses FFmpeg surely a significant set of functionality should be available ?

    Though I think this should work, my next best option would be using a separate ffmpeg library, which would ironically add another ffmpeg.dll to my solution I imagine. Any suggestion appreciated !

    Code fragment (using any video encoding API) :

    VideoWriter writer;
    
int codec = VideoWriter::fourcc('X', '2', '6', '4');
    
writer.open("test.avi", codec, 30, colorImage.size(), true);
    
writer.write(colorImage);
    
writer.release();

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