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View Full Version : NBC feed switching to 1080p24 mid-gop - how to handle?

dumbledore
3rd February 2013, 22:53
hi all

i am trying to demultiplex a mpeg-2 .ts stream I captured from NBC. there are a lot of times the frame PTSs don't match up with the gop delared FPS of 30000/1001 - in these gops, every other frame has 1501.5 additional delay added to its PTS. according to my calculations ((2*3303 + 1501.5) / 2 / 90 / 1000)^-1 comes out to 24p. inspecting the video stream shows that the frames are not interlaced either. (or at least, don't have any interlacing artifacts, even during motion.) is there a way to demux such a stream to an ES? the annoying part is that it doesn't switch at gop boundary but instead mid-gop, so i can't just change the framerate of whole gop to 24p. my best idea so far is to just duplicate the 4th frame, essentially doing the telecine myself so that the framerate matches up with the one in the seq header. is this a normal thing for hdtv or is it something new they are doing now?
kieranrk
4th February 2013, 00:34
The timestamps are unrelated to ES demux.
drmpeg
4th February 2013, 01:41
Is this a normal thing for hdtv or is it something new they are doing now?

It is normal for HDTV in general. However, if you only capture from OTA, then it's not as common. CBS is still using Harris encoders, which do not have inverse telecine. FOX and ABC are 720p, and although you can do inverse telecine with 720p, there are some decoders that have a difficult time so stations turn IVTC off.

NBC stations do use IVTC, but a real-time encoder can drop back to video at any time. Here's a command prompt utility that dumps the IVTC flags in an MPEG-2 elementary stream.

http://www.w6rz.net/flags.zip

The output looks like this (showing some drops to video when progressive_frame = 0):


C:\xfer>flags bits0001.mpv
GOP size = 45, byte index = 0
Tref = 0, TFF = 0, RFF = 0, PF = 1, I frame bits = 1102696
Tref = 1, TFF = 0, RFF = 1, PF = 1, P frame bits = 577928
Tref = 2, TFF = 1, RFF = 0, PF = 1, P frame bits = 558616
Tref = 3, TFF = 1, RFF = 1, PF = 1, P frame bits = 613024
Tref = 4, TFF = 0, RFF = 0, PF = 1, P frame bits = 736192
Tref = 5, TFF = 0, RFF = 1, PF = 1, P frame bits = 691832
Tref = 6, TFF = 1, RFF = 0, PF = 1, P frame bits = 639400
Tref = 7, TFF = 1, RFF = 1, PF = 1, P frame bits = 639744
Tref = 8, TFF = 0, RFF = 0, PF = 1, P frame bits = 798856
Tref = 9, TFF = 0, RFF = 1, PF = 1, P frame bits = 623176
Tref = 10, TFF = 1, RFF = 0, PF = 1, P frame bits = 525424
Tref = 11, TFF = 1, RFF = 1, PF = 1, P frame bits = 788208
Tref = 12, TFF = 0, RFF = 0, PF = 1, P frame bits = 480696
Tref = 13, TFF = 0, RFF = 1, PF = 1, P frame bits = 635008
Tref = 14, TFF = 1, RFF = 0, PF = 1, P frame bits = 735976
Tref = 15, TFF = 1, RFF = 1, PF = 1, P frame bits = 571752
Tref = 16, TFF = 0, RFF = 0, PF = 1, P frame bits = 815944
Tref = 17, TFF = 0, RFF = 1, PF = 1, P frame bits = 631336
Tref = 18, TFF = 1, RFF = 0, PF = 1, P frame bits = 565720
Tref = 19, TFF = 1, RFF = 1, PF = 1, P frame bits = 773064
Tref = 20, TFF = 0, RFF = 0, PF = 1, P frame bits = 506240
Tref = 21, TFF = 0, RFF = 1, PF = 1, P frame bits = 538552
Tref = 22, TFF = 1, RFF = 0, PF = 1, P frame bits = 682128
Tref = 23, TFF = 1, RFF = 1, PF = 1, P frame bits = 722648
Tref = 24, TFF = 0, RFF = 0, PF = 1, P frame bits = 561944
Tref = 25, TFF = 0, RFF = 1, PF = 1, P frame bits = 694656
Tref = 26, TFF = 1, RFF = 0, PF = 1, P frame bits = 553952
Tref = 27, TFF = 1, RFF = 1, PF = 1, P frame bits = 558296
Tref = 28, TFF = 0, RFF = 0, PF = 1, P frame bits = 620184
Tref = 29, TFF = 0, RFF = 1, PF = 1, P frame bits = 709056
Tref = 30, TFF = 1, RFF = 0, PF = 1, P frame bits = 577448
Tref = 31, TFF = 1, RFF = 1, PF = 1, P frame bits = 541768
Tref = 32, TFF = 0, RFF = 0, PF = 1, P frame bits = 516672
Tref = 33, TFF = 0, RFF = 1, PF = 1, P frame bits = 461192
Tref = 34, TFF = 1, RFF = 0, PF = 1, P frame bits = 506400
Tref = 35, TFF = 1, RFF = 1, PF = 1, P frame bits = 594648
Tref = 36, TFF = 0, RFF = 0, PF = 1, P frame bits = 569432
Tref = 37, TFF = 0, RFF = 1, PF = 1, P frame bits = 520504
Tref = 38, TFF = 1, RFF = 0, PF = 1, P frame bits = 487304
Tref = 39, TFF = 1, RFF = 1, PF = 1, P frame bits = 887496
Tref = 40, TFF = 0, RFF = 0, PF = 1, P frame bits = 572496
Tref = 41, TFF = 0, RFF = 1, PF = 1, P frame bits = 852584
Tref = 42, TFF = 1, RFF = 0, PF = 1, P frame bits = 764352
Tref = 43, TFF = 1, RFF = 1, PF = 1, P frame bits = 700744
Tref = 44, TFF = 0, RFF = 0, PF = 1, P frame bits = 463008
GOP size = 45, byte index = 3583537
Tref = 0, TFF = 0, RFF = 1, PF = 1, I frame bits = 908112
Tref = 1, TFF = 1, RFF = 0, PF = 1, P frame bits = 462152
Tref = 2, TFF = 1, RFF = 1, PF = 1, P frame bits = 715216
Tref = 3, TFF = 0, RFF = 0, PF = 1, P frame bits = 548240
Tref = 4, TFF = 0, RFF = 1, PF = 1, P frame bits = 494584
Tref = 5, TFF = 1, RFF = 0, PF = 1, P frame bits = 392352
Tref = 6, TFF = 1, RFF = 1, PF = 1, P frame bits = 635152
Tref = 7, TFF = 0, RFF = 0, PF = 1, P frame bits = 469968
Tref = 8, TFF = 0, RFF = 1, PF = 1, P frame bits = 606368
Tref = 9, TFF = 1, RFF = 0, PF = 1, P frame bits = 405328
Tref = 10, TFF = 1, RFF = 1, PF = 1, P frame bits = 634152
Tref = 11, TFF = 0, RFF = 0, PF = 1, P frame bits = 712416
Tref = 12, TFF = 0, RFF = 1, PF = 1, P frame bits = 685056
Tref = 13, TFF = 1, RFF = 0, PF = 1, P frame bits = 691512
Tref = 14, TFF = 1, RFF = 1, PF = 1, P frame bits = 707104
Tref = 15, TFF = 0, RFF = 0, PF = 1, P frame bits = 685864
Tref = 16, TFF = 0, RFF = 1, PF = 1, P frame bits = 601232
Tref = 17, TFF = 1, RFF = 0, PF = 1, P frame bits = 727688
Tref = 18, TFF = 1, RFF = 1, PF = 1, P frame bits = 838016
Tref = 19, TFF = 0, RFF = 0, PF = 1, P frame bits = 779192
Tref = 20, TFF = 0, RFF = 1, PF = 1, P frame bits = 633328
Tref = 21, TFF = 1, RFF = 0, PF = 1, P frame bits = 513168
Tref = 22, TFF = 1, RFF = 0, PF = 1, P frame bits = 627376
Tref = 23, TFF = 1, RFF = 0, PF = 0, P frame bits = 917656
Tref = 24, TFF = 1, RFF = 0, PF = 0, P frame bits = 755944
Tref = 25, TFF = 1, RFF = 0, PF = 0, P frame bits = 1037880
Tref = 26, TFF = 1, RFF = 0, PF = 0, P frame bits = 944664
Tref = 27, TFF = 1, RFF = 1, PF = 1, P frame bits = 926432
Tref = 28, TFF = 0, RFF = 0, PF = 1, P frame bits = 982600
Tref = 29, TFF = 0, RFF = 1, PF = 1, P frame bits = 799192
Tref = 30, TFF = 1, RFF = 0, PF = 1, P frame bits = 724408
Tref = 31, TFF = 1, RFF = 1, PF = 1, P frame bits = 987104
Tref = 32, TFF = 0, RFF = 0, PF = 1, P frame bits = 958152
Tref = 33, TFF = 0, RFF = 1, PF = 1, P frame bits = 763760
Tref = 34, TFF = 1, RFF = 0, PF = 1, P frame bits = 770792
Tref = 35, TFF = 1, RFF = 1, PF = 1, P frame bits = 766344
Tref = 36, TFF = 0, RFF = 0, PF = 1, P frame bits = 753456
Tref = 37, TFF = 0, RFF = 1, PF = 1, P frame bits = 733568
Tref = 38, TFF = 1, RFF = 0, PF = 1, P frame bits = 801984
Tref = 39, TFF = 1, RFF = 1, PF = 1, P frame bits = 827616
Tref = 40, TFF = 0, RFF = 0, PF = 1, P frame bits = 857864
Tref = 41, TFF = 0, RFF = 1, PF = 1, P frame bits = 826904
Tref = 42, TFF = 1, RFF = 0, PF = 1, P frame bits = 836608
Tref = 43, TFF = 1, RFF = 0, PF = 1, P frame bits = 862656
Tref = 44, TFF = 1, RFF = 0, PF = 0, P frame bits = 675608
GOP size = 33, byte index = 7706633
Tref = 0, TFF = 1, RFF = 0, PF = 0, I frame bits = 1480976
Tref = 1, TFF = 1, RFF = 0, PF = 0, P frame bits = 398864
Tref = 2, TFF = 1, RFF = 0, PF = 0, P frame bits = 560128
Tref = 3, TFF = 1, RFF = 1, PF = 1, P frame bits = 487000
Tref = 4, TFF = 0, RFF = 0, PF = 1, P frame bits = 490840
Tref = 5, TFF = 0, RFF = 1, PF = 1, P frame bits = 657088
Tref = 6, TFF = 1, RFF = 0, PF = 1, P frame bits = 604408
Tref = 7, TFF = 1, RFF = 1, PF = 1, P frame bits = 757648
Tref = 8, TFF = 0, RFF = 0, PF = 1, P frame bits = 737224
Tref = 9, TFF = 0, RFF = 1, PF = 1, P frame bits = 676416
Tref = 10, TFF = 1, RFF = 0, PF = 1, P frame bits = 745976
Tref = 11, TFF = 1, RFF = 1, PF = 1, P frame bits = 941720
Tref = 12, TFF = 0, RFF = 0, PF = 1, P frame bits = 978072
Tref = 13, TFF = 0, RFF = 1, PF = 1, P frame bits = 856712
Tref = 14, TFF = 1, RFF = 0, PF = 1, P frame bits = 820400
Tref = 15, TFF = 1, RFF = 0, PF = 1, P frame bits = 1021080
Tref = 16, TFF = 1, RFF = 0, PF = 0, P frame bits = 838568
Tref = 17, TFF = 1, RFF = 0, PF = 0, P frame bits = 925432
Tref = 18, TFF = 1, RFF = 0, PF = 0, P frame bits = 763744
Tref = 19, TFF = 1, RFF = 0, PF = 0, P frame bits = 790976
Tref = 20, TFF = 1, RFF = 1, PF = 1, P frame bits = 681360
Tref = 21, TFF = 0, RFF = 0, PF = 1, P frame bits = 558544
Tref = 22, TFF = 0, RFF = 1, PF = 1, P frame bits = 579832
Tref = 23, TFF = 1, RFF = 0, PF = 1, P frame bits = 552968
Tref = 24, TFF = 1, RFF = 1, PF = 1, P frame bits = 410784
Tref = 25, TFF = 0, RFF = 0, PF = 1, P frame bits = 352240
Tref = 26, TFF = 0, RFF = 1, PF = 1, P frame bits = 833904
Tref = 27, TFF = 1, RFF = 0, PF = 1, P frame bits = 743920
Tref = 28, TFF = 1, RFF = 1, PF = 1, P frame bits = 385656
Tref = 29, TFF = 0, RFF = 0, PF = 1, P frame bits = 473000
Tref = 30, TFF = 0, RFF = 1, PF = 1, P frame bits = 294080
Tref = 31, TFF = 1, RFF = 0, PF = 1, P frame bits = 273184
Tref = 32, TFF = 1, RFF = 1, PF = 1, P frame bits = 480704
GOP size = 45, byte index = 10475814
Tref = 0, TFF = 0, RFF = 0, PF = 1, I frame bits = 1040320
Tref = 1, TFF = 0, RFF = 1, PF = 1, P frame bits = 545416
Tref = 2, TFF = 1, RFF = 0, PF = 1, P frame bits = 1007752
Tref = 3, TFF = 1, RFF = 1, PF = 1, P frame bits = 865160
Tref = 4, TFF = 0, RFF = 0, PF = 1, P frame bits = 505544
Tref = 5, TFF = 0, RFF = 1, PF = 1, P frame bits = 452336
Tref = 6, TFF = 1, RFF = 0, PF = 1, P frame bits = 411392
Tref = 7, TFF = 1, RFF = 1, PF = 1, P frame bits = 802560
Tref = 8, TFF = 0, RFF = 0, PF = 1, P frame bits = 777016
Tref = 9, TFF = 0, RFF = 1, PF = 1, P frame bits = 329736
Tref = 10, TFF = 1, RFF = 0, PF = 1, P frame bits = 328648
Tref = 11, TFF = 1, RFF = 1, PF = 1, P frame bits = 427944
Tref = 12, TFF = 0, RFF = 0, PF = 1, P frame bits = 739392
Tref = 13, TFF = 0, RFF = 1, PF = 1, P frame bits = 715528
Tref = 14, TFF = 1, RFF = 0, PF = 1, P frame bits = 513688
Tref = 15, TFF = 1, RFF = 1, PF = 1, P frame bits = 410944
Tref = 16, TFF = 0, RFF = 0, PF = 1, P frame bits = 502888
Tref = 17, TFF = 0, RFF = 1, PF = 1, P frame bits = 523000
Tref = 18, TFF = 1, RFF = 0, PF = 1, P frame bits = 427688
Tref = 19, TFF = 1, RFF = 1, PF = 1, P frame bits = 462608
Tref = 20, TFF = 0, RFF = 0, PF = 1, P frame bits = 562168
Tref = 21, TFF = 0, RFF = 1, PF = 1, P frame bits = 621776
Tref = 22, TFF = 1, RFF = 0, PF = 1, P frame bits = 614896
Tref = 23, TFF = 1, RFF = 1, PF = 1, P frame bits = 489560
Tref = 24, TFF = 0, RFF = 0, PF = 1, P frame bits = 534816
Tref = 25, TFF = 0, RFF = 1, PF = 1, P frame bits = 355816
Tref = 26, TFF = 1, RFF = 0, PF = 1, P frame bits = 264248
Tref = 27, TFF = 1, RFF = 1, PF = 1, P frame bits = 336728
Tref = 28, TFF = 0, RFF = 0, PF = 1, P frame bits = 260136
Tref = 29, TFF = 0, RFF = 1, PF = 1, P frame bits = 474816
Tref = 30, TFF = 1, RFF = 0, PF = 1, P frame bits = 525072
Tref = 31, TFF = 1, RFF = 1, PF = 1, P frame bits = 400608
Tref = 32, TFF = 0, RFF = 0, PF = 1, P frame bits = 374808
Tref = 33, TFF = 0, RFF = 1, PF = 1, P frame bits = 412888
Tref = 34, TFF = 1, RFF = 0, PF = 1, P frame bits = 481792
Tref = 35, TFF = 1, RFF = 1, PF = 1, P frame bits = 400280
Tref = 36, TFF = 0, RFF = 0, PF = 1, P frame bits = 376024
Tref = 37, TFF = 0, RFF = 1, PF = 1, P frame bits = 407992
Tref = 38, TFF = 1, RFF = 0, PF = 1, P frame bits = 403240
Tref = 39, TFF = 1, RFF = 1, PF = 1, P frame bits = 451424
Tref = 40, TFF = 0, RFF = 0, PF = 1, P frame bits = 435520
Tref = 41, TFF = 0, RFF = 1, PF = 1, P frame bits = 451448
Tref = 42, TFF = 1, RFF = 0, PF = 1, P frame bits = 516056
Tref = 43, TFF = 1, RFF = 1, PF = 1, P frame bits = 700008
Tref = 44, TFF = 0, RFF = 0, PF = 1, P frame bits = 817496


Ron
dumbledore
4th February 2013, 02:09
interesting. i was assuming that if i just demuxed the raw es then the PTS gaps would lead to the audio going gradually OOS, since PTS is stripped when writing the ES. the TFF/RFF/PF flags should tell the decoder to use the correct frame rate though?
drmpeg
4th February 2013, 02:29
interesting. i was assuming that if i just demuxed the raw es then the PTS gaps would lead to the audio going gradually OOS, since PTS is stripped when writing the ES. the TFF/RFF/PF flags should tell the decoder to use the correct frame rate though?

Unfortunately, most software decoders will not actually repeat a field when RFF = 1. So yes, you'll have A/V sync drift when re-encoding.

Ron