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author | Nicolas George <nicolas.george@normalesup.org> | 2010-11-11 18:24:11 +0300 |
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committer | Nicolas George <nicolas.george@normalesup.org> | 2010-11-11 18:24:11 +0300 |
commit | ba83c4bfb55d5c3fc6b3959edb0d3cda07a70241 (patch) | |
tree | 6fc4a3763a476c355f9efd4cf0713b65a2c4368a /doc | |
parent | 2c5168afed8ddd798dae5909dba85ae3b611f894 (diff) |
MJPEG/AVI1 to JPEG/JFIF bitstream filter.
Originally committed as revision 25721 to svn://svn.ffmpeg.org/ffmpeg/trunk
Diffstat (limited to 'doc')
-rw-r--r-- | doc/bitstream_filters.texi | 37 | ||||
-rw-r--r-- | doc/ffmpeg-doc.texi | 2 |
2 files changed, 38 insertions, 1 deletions
diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi index 0bcb6c7f60..1ad67cd5ef 100644 --- a/doc/bitstream_filters.texi +++ b/doc/bitstream_filters.texi @@ -25,6 +25,43 @@ Below is a description of the currently available bitstream filters. @section imx_dump_header +@section mjpeg2jpeg + +Convert MJPEG/AVI1 packets to full JPEG/JFIF packets. + +MJPEG is a video codec wherein each video frame is essentially a +JPEG image. The individual frames can be extracted without loss, +e.g. by + +@example +ffmpeg -i ../some_mjpeg.avi -vcodec copy frames_%d.jpg +@end example + +Unfortunately, these chunks are incomplete JPEG images, because +they lack the DHT segment required for decoding. Quoting from +@url{http://www.digitalpreservation.gov/formats/fdd/fdd000063.shtml}: + +Avery Lee, writing in the rec.video.desktop newsgroup in 2001, +commented that "MJPEG, or at least the MJPEG in AVIs having the +MJPG fourcc, is restricted JPEG with a fixed -- and *omitted* -- +Huffman table. The JPEG must be YCbCr colorspace, it must be 4:2:2, +and it must use basic Huffman encoding, not arithmetic or +progressive. . . . You can indeed extract the MJPEG frames and +decode them with a regular JPEG decoder, but you have to prepend +the DHT segment to them, or else the decoder won't have any idea +how to decompress the data. The exact table necessary is given in +the OpenDML spec." + +This bitstream filter patches the header of frames extracted from an MJPEG +stream (carrying the AVI1 header ID and lacking a DHT segment) to +produce fully qualified JPEG images. + +@example +ffmpeg -i mjpeg-movie.avi -vcodec copy -vbsf mjpeg2jpeg frame_%d.jpg +exiftran -i -9 frame*.jpg +ffmpeg -i frame_%d.jpg -vcodec copy rotated.avi +@end example + @section mjpega_dump_header @section movsub diff --git a/doc/ffmpeg-doc.texi b/doc/ffmpeg-doc.texi index b33ea5e7b4..e2e0df7f2f 100644 --- a/doc/ffmpeg-doc.texi +++ b/doc/ffmpeg-doc.texi @@ -522,7 +522,7 @@ Force video tag/fourcc. @item -qphist Show QP histogram. @item -vbsf @var{bitstream_filter} -Bitstream filters available are "dump_extra", "remove_extra", "noise", "h264_mp4toannexb", "imxdump", "mjpegadump". +Bitstream filters available are "dump_extra", "remove_extra", "noise", "h264_mp4toannexb", "imxdump", "mjpegadump", "mjpeg2jpeg". @example ffmpeg -i h264.mp4 -vcodec copy -vbsf h264_mp4toannexb -an out.h264 @end example |