Re: [FFmpeg-devel] [PATCH 1/3] ffmpeg: Don't print graphs if there are no graphs to print

[Mark Thompson <sw@jkqxz.net>]

On 17/05/2025 18:52, softworkz . wrote:
> 
> 
>> -----Original Message-----
>> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Mark
>> Thompson
>> Sent: Samstag, 17. Mai 2025 13:14
>> To: ffmpeg-devel@ffmpeg.org
>> Subject: [FFmpeg-devel] [PATCH 1/3] ffmpeg: Don't print graphs if there are no
>> graphs to print
>>
>> Avoids writing an empty json blob in setup error cases.
>> ---
>>  fftools/ffmpeg.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
>> index 964770df23..ad28cff78d 100644
>> --- a/fftools/ffmpeg.c
>> +++ b/fftools/ffmpeg.c
>> @@ -309,7 +309,8 @@ const AVIOInterruptCB int_cb = { decode_interrupt_cb, NULL
>> };
>>
>>  static void ffmpeg_cleanup(int ret)
>>  {
>> -    if (print_graphs || print_graphs_file)
>> +    if ((print_graphs || print_graphs_file) &&
>> +        (nb_filtergraphs > 0 || nb_output_files > 0))
>>          print_filtergraphs(filtergraphs, nb_filtergraphs, input_files,
>> nb_input_files, output_files, nb_output_files);
> 
> The feature is not just about filter graphs, that's why it's been renamed
> as "Execution Graph Printing". It also works when no filter graphs are
> in play at all. 
> Here's an example:
> 
> https://softworkz.github.io/ffmpeg_output_apis/1_nofilters_3_in_1_out.html
> 
> 
> As for the nb_output_files check, I'm not sure - is it 0 or 1 in case of
> -f null output?

1, including when you stream copy to null and there aren't any real graphs.  At least one output is mandatory for a valid command line, so it should always appear in non-error cases as far as I am aware.

The aim is to avoid to the nonsense json blob when an early error happens - example below.  It does still get printed on later errors (such as a muxer error), because the graph is created then and some operations will have happened at that point.

Thanks,

- Mark


$ ./ffmpeg_g -print_graphs -i nonexistent -f null -
...
[in#0 @ 0x513000000200] Error opening input: No such file or directory
Error opening input file nonexistent.
Error opening input files: No such file or directory
{
    "graphs": [

    ],
    "inputfiles": [
        {
            "index": "0",
            "inputstreams": [

            ]
        }
    ],
    "decoders": [

    ],
    "encoders": [

    ],
    "outputfiles": [

    ],
    "streamlinks": [

    ]
}

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