[FFmpeg-devel] DVR MPEG4 variant (AS-3024)

[Paul B Mahol]

On 2/3/17, Ivo Andonov <ivo.andonov at gmail.com> wrote:
> Hi Everyone,
>
> This is my first post here. Actually my first post to a mailing list.
> Excuse me if this is the wrong place to write or if my mailing-list culture
> is not complete!
>
> I've got some old Pinetron DVRs that are supposed to produce a MPEG4
> bitstream. Indeed they are but no non-Pinetron software can decode it.
> While changing the realtime clock battery on one of these I saw they are
> using the AS-3024 SoC. Any information about it is quite rare and hard to
> find. What I found in a kind of a brochure is the "Modified ISO/IEC
> 14496/2" statement.
>
> I successfully used a modified Pinetron library on Windows to use my own
> software for decoding the stream. While fiddling with the modification I
> saw they are using the statically linked FFmpeg API.
>
> Out of curiosity and wanting to have this codec implementation on the Linux
> platform to automate some tasks I digged deeper in order to understand the
> decoder difference in respect to the standards. The codec name they use is
> xvid_alogics.
>
> Finally there's the result and I wanted to share it with the comunity in
> case someone is interested or if one wants to use it for its own project.
>
> In short, what I did is modify libavcodec/mpeg4video.h, ff_mpeg4_pred_dc
> function and add the lines of code below right after the a, b, c vars being
> initialized and instead of the block of code that sets the pred var.
>
>       if (n == 0 || n == 4 || n == 5) pred = 1024; else
>       if (n == 1) pred = a; else
>       if (n == 2) pred = c; else
>       if (n == 3) {
>         if (abs(a - b) < abs(b - c)) {
>           pred     = c;
>         } else {
>           pred     = a;
>         }
>       }
>
> I do now know what is the best approach for registering this as a new
> decoder and then having the above block within a condition. What I came up
> with is adding a new AVCodec to the mpeg4videodec.c file and modifying the
> decode_init to set a flag in AVCodecContext.workaround_bugs field that can
> later be used to condition the above block.

Why not share your code modifications and samples?