Thursday, April 17, 2008

BD/AVCHD vs. AppleTV and NAS.

BD is crap as movie storage. It needs 1 sec. GOP and that implies higher bitrates, bigger files, etc. Inefficient. Plus ffdshow craps out playing files with GOP with less then 60-90 frames. AVCHD allows longer GOP, but needs interlaced SD with LPCM audio (HD needs AC3 and 720 is all progressive and 1080 could only be progressive at 24p). So out of the box I could only try 720p24 and 720p60 and that means that for both BD and AVCHD I would have to frame-reduce my 720p30 Aiptek mp4, i.e. would have to transcode which is bad.

For 720p I would have to frame-reduce 1080i downconverts (and probably 720p60 originals) to 23.976 fps. 60i (for 1080 and SD) means 29.97 frames which could be 24p pull-downed, 29.97 interlaced and 29.97 progressive with pulldown flag set on h.264 stream. Apparently x264 could set pulldown flag with "--pulldown 23" (might not be fully supported in hbcli) and all streams need to be encoded with --aud and --nal-hdr (the later again might not be supported in hbcli), but overall it looks like AVCHD/BD is still being in its early days after a year of hacking... Additionally, QT cannot play 60i streams but could play 23.976 with pull-down disregard pull-down flag. Thus overall AVCHD/BD is good only for 720p24 and in order to play on both BD standalone and Apple TV everything need to be frame-reduced which is bad. (Theoretically, I could store 720p60, but at 4+xT even on Q6600 and 5Mbps bitrates it ain't worth it).

So there you have it - there is absolutely no reason to encode BD compliant streams and thus BD brings nothing new to viewing HD at home and solution remains the same - encode for storage on NAS and view thru networked TV appliance. Welcome back Apple TV.

Before completely giving up on BD and AVCHD however still try couple things:

  1. Try Nero Vision 8 to see if it would try to transcode my 720p24. If it would try another 720p24 encoded with --detelecine -r 23.976 -x pulldown=23:aud=1:nal-hdr=1
  2. Try Nero with 720x480@24p with pull-down and see if motion jerks because of the frame-reduction on say Seige or 60_seconds.
  3. Try using seek and frames with HB.
P.S. Both BD and AVCHD wrap streams into MPEG-2 transport, mpg program stream cannot store PCM, thus VHS MPEG-2 encodes have .mp2 audio and for SD I would have to unencode .aac from .mp4 while for HD AC3 need to be copied over from the original and AC3 cannot be stored in .mp4...

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