[FFmpeg-devel] [PATCH] fftools/ffmpeg_filter: add -print_filter_graph option

[Nicolas George]

Niklas Haas (HE12025-02-17):
> From: Niklas Haas <git at haasn.dev>
> 
> This developer tool is especially handy when debugging filter graph
> auto-negotiation, although it can be useful in whatever scenario to
> get a canonical dump of the fully settled filter graph.
> 
> To make the result slightly more useful, we omit buffersrc/buffersink
> filters and instead print the corresponding input/output name. Sadly, this
> is lossy w.r.t. the link names used in the original filter graph, although
> the result has the advantage of being in a normalized format.
> 
> As an example, the following filter graph (taken from FATE):
> 
>   sws_flags=+accurate_rnd+bitexact;
>   split [main][over];
>   [over] scale=88:72, pad=96:80:4:4 [overf];
>   [main][overf] overlay=240:16:format=yuv422
> 
> Results in this output:
> 
> Filter graph:
>   [0:0] split=thread_type=0x00000000 [L0] [L1];
>   [L1] scale=w=88:width=88:h=72:height=72:flags=+accurate_rnd+bitexact:thread_type=0x00000000 [L2];
>   [L2] pad=width=96:w=96:height=80:h=80:x=4:y=4:thread_type=0x00000000 [L3];
>   [L4] [L3] overlay=x=240:y=16:format=2 [#0:0];
>   [L0] scale=w=iw:width=iw:h=ih:height=ih:flags=+accurate_rnd+bitexact:thread_type=0x00000000 [L4];
> Filter links:
>   L0: yuv420p 352x288 [SAR 0:1] csp:unknown range:tv
>   L1: yuv420p 352x288 [SAR 0:1] csp:unknown range:tv
>   L2: yuva422p 88x72 [SAR 0:1] csp:unknown range:tv
>   L3: yuva422p 96x80 [SAR 0:1] csp:unknown range:tv
>   L4: yuva422p 352x288 [SAR 0:1] csp:unknown range:tv
> 
> I do acknowledge the overlap between this and avfilter/graphdump.c, but there
> are a couple of important deviations:
> 

> 1. graphdump.c prints a "pretty printed" ASCII art graph for human consumption,
>    but the goal here is to print it in a format that can be passed back to
>    -filter_complex.

The ASCII art output is shitty indeed. But notice that
avfilter_graph_dump() takes an options argument that is set from the
argument of the dumpgraph option. This is precisely meant to allow
future different output formats.

> 2. graphdump.c does not know anything about buffersrc/buffersink filters or
>    input/output names, which is why this implementation has to live inside
>    ffmpeg_filter.c.

I find this a very feeble reason to duplicate the feature.

> It's possible that we could instead move this implementation to graphdump.c as
> well, though that would require some sort of explicit callback to get the names
> for buffer sources / sinks, to avoid breaking the first design goal.

It would be enough to add “const char *name_in, *name_out;” to
AVFilterLink. Or a single parsed_name field to AVFilterPad.

Regards,

-- 
  Nicolas George