Hi Hans, Thanks for looking into. I remember MJPEG vs. JPEG being a source of confusion for me a few years ago, so clarification is greatly welcome :-) On Mon, 2018-10-01 at 15:03 +0300, Laurent Pinchart wrote: > Hi Hans, > > On Monday, 1 October 2018 14:54:29 EEST Hans Verkuil wrote: > > On 10/01/2018 01:48 PM, Laurent Pinchart wrote: > > > On Monday, 1 October 2018 11:43:04 EEST Hans Verkuil wrote: > > > > It turns out that we have both JPEG and Motion-JPEG pixel formats > > > > defined. > > > > > > > > Furthermore, some drivers support one, some the other and some both. > > > > > > > > These pixelformats both mean the same. > > > > > > Do they ? I thought MJPEG was JPEG using fixed Huffman tables that were > > > not included in the JPEG headers. > > > > I'm not aware of any difference. If there is one, then it is certainly not > > documented. > > What I can tell for sure is that many UVC devices don't include Huffman tables > in their JPEG headers. > > > Ezequiel, since you've been working with this recently, do you know anything > > about this? > > JPEG frames must include huffman and quantization tables, as per the standard. AFAIK, there's no MJPEG specification per-se and vendors specify its own way of conveying a Motion JPEG stream. For instance, omiting the huffman table seems to be a vendor thing. Microsoft explicitly omits the huffman tables from each frame: https://www.fileformat.info/format/bmp/spec/b7c72ebab8064da48ae5ed0c053c67a4/view.htm Others could be following the same things. Like I mentioned before, Gstreamer always check for missing huffman table and adds one if missing. Gstreamer has other quirks for missing markers, e.g. deal with a missing EOI: https://github.com/GStreamer/gst-plugins-good/commit/10ff3c8e14e8fba9e0a5d696dce0bea27de644d7 I think Hans suggestion of settling on JPEG makes sense and it would be consistent with Gstreamer. Otherwise, we should specify exactly what we understand by MJPEG, but I don't think it's worth it. Thanks, Ezequiel
