On Sat, Aug 12, 2017 at 9:47 AM, Dave Rice <d...@dericed.com> wrote: > > Hello all, > This issue originated in this thread > https://github.com/amiaopensource/vrecord/issues/170. On Field Order, in the > QuickTime specification at > https://developer.apple.com/library/content/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html > (and similarly in the Matroska specification which adopted similar language) > it states the following meanings for field order values: > > > 9 – B is displayed earliest, T is stored first in the file. 14 – T is > > displayed earliest, B is stored first in the file. > > This definition is contradicted by other Apple documentation such as > https://developer.apple.com/library/content/technotes/tn2162/_index.html#//apple_ref/doc/uid/DTS40013070-CH1-TNTAG10-THE__FIEL__IMAGEDESCRIPTION_EXTENSION__FIELD_FRAME_INFORMATION. > > An Apple engineer confirmed that the QuickTime specification’s definitions > for those Field Order values is wrong and does not match Apple’s (of > FFmpeg’s) practice, see > https://github.com/amiaopensource/vrecord/issues/170#issuecomment-321937668. > > However I think that some of the commenting in ffmpeg is based upon the > inaccurate definitions from Apple. For instance, in that thread David Singer > confirms: > > > Ah, not quite. 1 and 6 are indeed 'planar' (all of one field before all of > > the other). They don't concern us. Both 9 and 14 are stored in spatial > > order (i.e. you could do terrible de-interlacing by simply displaying the > > buffer as a frame), and the 9 or 14 value tells you which field is to be > > displayed first. > > > > 9 – T is earlier than B. 14 – B is earlier than T > > mov.c associates AV_FIELD_TB with 9 and AV_FIELD_BT with 14 (similar > associations in matroska.h), but avcodec.h states: > > > AV_FIELD_TB, //< Top coded first, bottom displayed first > > AV_FIELD_BT, //< Bottom coded first, bottom displayed first > > IMHO in both cases of AV_FIELD_TB and AV_FIELD_BT the coding should be > referred as interleaved rather than ‘bottom coded first’ or ‘top coded > first’. In the case of AV_FIELD_TT and AV_FIELD_BB the fields are stored as > planar images where storage order is notable, but with TB and BT the fields > are interleaved. > > Also utils.c associates these field order values with the following labels: > > > AV_FIELD_TB -> "top coded first (swapped)"; > > AV_FIELD_BT -> "bottom coded first (swapped)"; > > From my reading, I infer that "top coded first (swapped)” means "top coded > first, bottom displayed first”; however in practice from files generated by > QuickTime and FFmpeg files with a value of TB have the top field displayed > first, so I think the labels are swapped. In the patch below I suggest using > “top first (interleaved)” for TB and “bottom first (interleaved)” for BT. > > Comments? >
Icefloe019 agrees with your changes: http://mirror.informatimago.com/next/developer.apple.com/quicktime/icefloe/dispatch019.html#fiel They seems reasonable to me. when I made this change originally my primary concern was getting the field info out of extradata. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
