[FFmpeg-devel] libavfilter: avfilter_graph_parse2 is not preserving pad names

[Paul B Mahol]

On 7/21/20, Paul B Mahol <onemda at gmail.com> wrote:
> On 7/14/20, Rahul Lodha <rahullodhas at gmail.com> wrote:
>> I wrote a code to mix two audio streams which is working. However,
>> somehow `avfilter_graph_parse2` is not preserving the pad names
>>
>> For example, below is a filter spec
>>
>> ```
>> filter_spec =
>> "abuffer=time_base=1/48000:sample_rate=48000:sample_fmt=fltp:channel_layout=0x3[a0]
>> ;
>> abuffer=time_base=1/48000:sample_rate=48000:sample_fmt=fltp:channel_layout=0x3
>> [a1];
>>  [a0] [a1] amix=inputs=2, abuffersink";
>> ```
>> Below is the code to parse and dump graph
>>
>> ```
>> if ((ret = avfilter_graph_parse2(filter_graph, filter_spec, &inputs,
>> &outputs)) < 0) {
>>                 av_log(NULL, AV_LOG_ERROR, "avfilter_graph_parse_ptr
>> failed: %d\n", ret);
>>         }
>>
>>         if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0) {
>>                 av_log(NULL, AV_LOG_ERROR, "avfilter_graph_config
>> failed\n");
>>         }
>>
>> char *g = avfilter_graph_dump(filter_graph, NULL);
>>         if(g) {
>>                 av_log(NULL, AV_LOG_ERROR, "Graph: %s\n", g);
>>                 av_free(g);
>>         }
>>
>> ```
>> and below is the graph dump.
>>
>> ```
>> Graph: +------------------+
>> | Parsed_abuffer_0 |default--[48000Hz fltp:stereo]--Parsed_amix_2:input0
>> |    (abuffer)     |
>> +------------------+
>>
>> +------------------+
>> | Parsed_abuffer_1 |default--[48000Hz fltp:stereo]--Parsed_amix_2:input1
>> |    (abuffer)     |
>> +------------------+
>>
>>                                                        +---------------+
>> Parsed_abuffer_0:default--[48000Hz fltp:stereo]--input0| Parsed_amix_2
>> |default--[48000Hz fltp:stereo]--Parsed_abuffersink_3:default
>> Parsed_abuffer_1:default--[48000Hz fltp:stereo]--input1|    (amix)     |
>>                                                        +---------------+
>>
>>
>> +----------------------+
>> Parsed_amix_2:default--[48000Hz fltp:stereo]--default|
>> Parsed_abuffersink_3
>> |
>>                                                      |    (abuffersink)
>> |
>>
>> +----------------------+
>>
>>
>>
>> ```
>>
>> As you can see, all the pad names a0, a1, etc gone and they are
>> replaced by `default`, Parsed_abuffersink_3 etc.
>>
>> Is there any way to preserve names?
>
> Such pad names are never preserved.
> Could they be preserved? Certainly yes. Patch welcome.

Also you can use "amix at amix_pad_name=options" when setting up filter
graph to set pad names.