Hi, Some time ago we were discussing the set of controls that should be implemented for codec support.
I remember that the result of this discussion was that the controls should be as "integrated" as possible. This included the V4L2_CID_MPEG_LEVEL and all controls related to the quantization parameter. The problem with such approach is that the levels are different for MPEG4, H264 and H263. Same for quantization parameter - it ranges from 1 to 31 for MPEG4/H263 and from 0 to 51 for H264. Having single controls for the more than one codec seemed as a good solution. Unfortunately I don't see a good option to implement it, especially with the control framework. My idea was to have the min/max values for QP set in the S_FMT call on the CAPTURE. For MPEG_LEVEL it would be checked in the S_CTRL callback and if it did not fit the chosen format it failed. So I see three solutions to this problem and I wanted to ask about your opinion. 1) Have a separate controls whenever the range or valid value range differs. This is the simplest and in my opinion the best solution I can think of. This way we'll have different set of controls if the valid values are different (e.g. V4L2_CID_MPEG_MPEG4_LEVEL, V4L2_CID_MPEG_H264_LEVEL). User can set the controls at any time. The only con of this approach is having more controls. 2) Permit the user to set the control only after running S_FMT on the CAPTURE. This approach would enable us to keep less controls, but would require to set the min/max values for controls in the S_FMT. This could be done by adding controls in S_FMT or by manipulating their range and disabling unused controls. In case of MPEG_LEVEL it would require s_ctrl callback to check whether the requested level is valid for the chosen codec. This would be somehow against the spec, but if we allow the "codec interface" to have some differences this would be ok. 3) Let the user set the controls whenever and check them during the STREAMON call. The controls could be set anytime, and the control range supplied to the control framework would cover values possible for all supported codecs. This approach is more difficult than first approach. It is worse in case of user space than the second approach - the user is unaware of any mistakes until the STREAMON call. The argument for this approach is the possibility to have a few controls less. So I would like to hear a comment about the above propositions. Personally I would opt for the first solution. Best regards, -- Kamil Debski Linux Platform Group Samsung Poland R&D Center -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
