Found it, of course the problem is memory management.
It would seem that avfilter_copy_buf_props reuses the buffer, allocating
it to the target frame rather than copying it. Unfortunately if you then
call avfilter_unref_buffer before encoding frame the front of the buffer
gets trampled on, introducing the clicks.
Ian
On 10/23/12 12:18, Ian Holbrough wrote:
Hi,
I'm in the process of migrating to libavfilter based resampling using
ffmpeg/libav 1.0 and the audio filter chain seems to be introducing
audio clicks. Setting up a passthrough chain with...
AVFilterContext* last = NULL;
filterAudGraph = avfilter_graph_alloc();
char args[255];
snprintf(args, 255,
"time_base=%d/%d:sample_rate=%d:sample_fmt=%s:channel_layout=0x%llx",
1, inpAudioCodec->sample_rate, inpAudioCodec->sample_rate,
av_get_sample_fmt_name(inpAudioCodec->sample_fmt),
inpAudioCodec->channel_layout);
filterAudInp = tsUtilsInitFilter("abuffer", "audInput", args,
NULL, filterAudGraph);
last = filterAudInp;
const enum AVSampleFormat formats[] = { AV_SAMPLE_FMT_S16, -1 };
AVABufferSinkParams* params = av_abuffersink_params_alloc();
params->sample_fmts = formats;
filterAudOut = tsUtilsInitFilter("ffabuffersink", "audOutput",
NULL, params, filterAudGraph);
av_free(params);
avfilter_link(last, 0, filterAudOut, 0);
avfilter_graph_config(filterAudGraph, NULL);
...where...
AVFilterContext* tsUtilsInitFilter(const char * filterName, const
char* name,
const char* arguments, void* opaque, AVFilterGraph* graph) {
AVFilter* filter = avfilter_get_by_name(filterName);
AVFilterContext* context = NULL;
int ret = avfilter_graph_create_filter(&context, filter, name,
arguments, opaque, graph);
if (ret < 0) {
die("tsUtilsInitFilter - failed to create filter context
<%s>", name);
}
return context;
}
...however, when a frame is added (I believe the input sample format,
rate and channel layout is compatible with the required output) who's
first few samples look like this...
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 ffffffff 00000000 00000000 00000000 00000000 00000000
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000001 00000000 00000001 00000000 00000000 00000000
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
ffffffff 00000000
ffffffff 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
...upon retrieving the same frame from the chain the first 4 samples
look somewhat different...
*000063f0 ffffb628 00002ff8 000008d9* 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 ffffffff 00000000 00000000 00000000 00000000 00000000
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000001 00000000 00000001 00000000 00000000 00000000
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
ffffffff 00000000
ffffffff 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
...the remainder of the frame is identical. These sample dumps are
produced by...
short* a = frame->data[0];
for (int i = 0; i != frame->nb_samples; i++) {
printf("%08x ", *(a++));
if ((i % 16) == 15) printf("\n");
}
....removing the filter chain and passing the decoded frames straight
through to the encoder does not produce clicking. Any suggestions as
to the cause would be gratefully received.
Regards
Ian
--
Ian Holbrough, Software Engineer
Yospace - Mobile Video Made Easy
Centurion House, London Road, Staines TW18 4AX
Switchboard: +44 (0)1784 466388
Fax: +44 (0)1784 466387
http://www.yospace.com
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