[FFmpeg-devel] [PATCH 9/9] ffplay: add -af option

[Marton Balint]

On Mon, 25 Jun 2012, Stefano Sabatini wrote:

[...]

>>> +    layouts[0] = avctx->channel_layout;
>>> +
>>> +    snprintf(abuffer_args, sizeof(abuffer_args), "sample_rate=%d:sample_fmt=%s:channel_layout=0x%"PRIx64,
>>> +             avctx->sample_rate,
>>> +             av_get_sample_fmt_name(avctx->sample_fmt),
>>> +             avctx->channel_layout);
>>> +    ret = avfilter_graph_create_filter(&filt_asrc,
>>> +                                       avfilter_get_by_name("abuffer"), "ffplay_abuffer",
>>> +                                       abuffer_args, NULL, is->agraph);
>>> +    if (ret < 0) goto fail;
>>> +
>>> +    abuffersink_params->sample_fmts     = sample_fmts;
>>> +    abuffersink_params->channel_layouts = layouts;
>>
>
>> Before calling audio_open using these are fine for determining the
>> normal output of the audio filters. But once the audio_open is
>> called, you should enforce the settings set in
>> VideoState->audio_tgt.
>
> So what about calling audio_open() and *then* configuring the
> filtergraph? This should be simpler than:
>
> configure_filters()
> audio_open()
> configure_filters() again
>

Only problem is that for audio open you have to request something as 
channel count and sample rate. It is better to request the number of 
channels and the sample rate the filter would normally output, but you can 
only determine that by configuring the filters once.

That is why I proposed to configure the filters before audio open to 
determine the preferred output channel count and sample rate of the 
filter, request that for audio_open and if audio_open can't handle that 
then reconfigure the filters with the real output settings audio_open has 
fallen back to.

[...]

Regards,
Marton