El 26/04/2017 a las 22:32, luigi escribió:
Hello,
I'm trying to decode effectively audio in an .avi video file with
decode_audio4, etc.
I succeed as long as the decoded frames are stereo, but when I bump
into avi files which have 5.1 channels I get weird audio reproduction.
I have so far tried to resample (swr_convert) the decoded frames, but
with no success.
av_opt_set_int(swr_ctx, "in_channel_layout", src_ch_layout, 0);
av_opt_set_int(swr_ctx, "in_sample_rate", src_rate, 0);
av_opt_set_sample_fmt(swr_ctx, "in_sample_fmt", src_sample_fmt, 0);
av_opt_set_int(swr_ctx, "in_channel_count", dec_fr->channels, 0);
av_opt_set_int(swr_ctx, "out_channel_layout", dst_ch_layout, 0);
av_opt_set_int(swr_ctx, "out_sample_rate", dst_rate, 0);
av_opt_set_sample_fmt(swr_ctx, "out_sample_fmt", dst_sample_fmt, 0);
av_opt_set_int(swr_ctx, "out_channel_count", 2, 0);
Here, I would like to ask a few questions:
1) is the "in_channel_layout" the layout of the decoded frame before
it is resampled?
Yes.
2) what is it that swr_convert really does?
It converts among different audio channels, mixing them sometimes.
For swr_convert to work you need to have called swr_init() before (after
you set the opts).
Example:
forw_ctx = swr_alloc_set_opts(NULL, out_ch_layout,
out_sample_fmt, out_sample_rate,
in_ch_layout, in_sample_fmt,
in_sample_rate,
0, NULL);
if(!forw_ctx) {
LOG_ERROR( _("Failed to alloc swresample
library") );
return 0;
}
if(swr_init(forw_ctx) < 0)
{
char buf[256];
av_get_channel_layout_string(buf, 256, -1,
in_ch_layout);
LOG_ERROR( _("Failed to init swresample library
with ")
<< buf << " "
<< av_get_sample_fmt_name(in_sample_fmt)
<< _(" frequency: ") <<
in_sample_rate );
return 0;
}
int len2 = swr_convert(forw_ctx, (uint8_t**)&samples,
_aframe->nb_samples, // No
resampling wanted
(const uint8_t
**)_aframe->extended_data,
_aframe->nb_samples );
--
Gonzalo Garramuño
_______________________________________________
Libav-user mailing list
[email protected]
http://ffmpeg.org/mailman/listinfo/libav-user
