On 10/11/2021 03:40, Jammy Huang wrote: > Dear Hans, > > On 2021/11/9 下午 06:17, Hans Verkuil wrote: >> On 11/9/21 2:56 AM, Jammy Huang wrote: >>> Dear Hans, >>> >>> Thanks for your review. >>> >>> On 2021/11/8 下午 05:09, Hans Verkuil wrote: >>>> On 22/10/2021 08:55, Jammy Huang wrote: >>>>> aspeed supports differential jpeg format which only compress the parts >>>>> which are changed. In this way, it reduces both the amount of data to be >>>>> transferred by network and those to be decoded on the client side. >>>>> >>>>> 4 new ctrls are added: >>>>> * Aspeed JPEG Format: to control aspeed's partial jpeg on/off >>>>> 0: standard jpeg, 1: aspeed jpeg >>>> What exactly is 'aspeed jpeg'? >>> 'aspeed jpeg' is aspeed proprietary compression format. It will compare >>> the new frame >>> with previous one to decide which macroblock's data is changed, and only >>> the changed >>> macroblock will be compressed. In this way, the amount of compressed data is >>> significantly reduced. This is similar to the concept of I/P-frames of >>> video compression. >> Right, but that makes this a new vendor-specific pixelformat, not a control. > OK, I will add a new vendor-specific pixelformat for this. >> >>> For example, the video is static in first 3 frames and then a object in >>> the video moved in >>> 4th frame. >>> >>> Frame Content | Standard | Aspeed >>> ----------------------------------------------------------------------- >>> 1th | Full | Full >>> 2th identical with 1st | Full | none (only about >>> 12 Bytes for header data) >>> 3th identical with 1st | Full | none >>> 4th a object moved | Full | Only the Macroblocks >>> that have data changed are compressed >>> >>> I have implemented a javascript aspeed decoder in novnc to support this >>> format, but >>> the performance isn't good enough. I am working on a web-assembly to >>> improve it. >> Is this format documented in a datasheet or something similar, ideally freely >> available? > This format is documented in ast2400/2500/2600's datasheet, but it's not > freely available. OK. Make sure to document the new pixelformat in Documentation/userspace-api/media/v4l/pixfmt-reserved.rst with a reference to where it is defined in the datasheet. If there is publicly available source code that converts it to 'normal' JPEG, then a reference to that would be very nice as well. >> >>>>> * Aspeed Compression Mode: to control aspeed's compression mode >>>>> 0: DCT Only, 1: DCT VQ mix 2-color, 2: DCT VQ mix 4-color >>>>> This is AST2400 only. It will adapt JPEG or VQ encoding method according >>>>> to the context automatically. >>>> What exactly does this do? >>>> >>>> Is this very aspeed-specific, or could this be a standard JPEG control? >>> Yes, this is aspeed-specific. Its compression algorithm is a modified >>> JPEG algorithm. >> Is this specific to the aspeed jpeg format, or also to the 'regular' jpeg format? > > It's specific to the aspeed jpeg format. Regular jpeg is based on DCT > and doesn't support VQ > compression OK, that makes it an aspeed-specific control. Good to know. Regards, Hans
