[FFmpeg-devel] Reducing time spent in av_find_stream_info()

[Diego Santa Cruz]

Hi there,

I am using ffmpeg on an embedded platform with a slow cpu (ARMv5 300 MHz, no FPU) and av_find_stream_info() is taking a long time on the audio streams (> 800 ms). Looking around I found that close to 99% of this time is spent updating duration_error for the audio stream. However, duration_error is only used for the video streams. I added an if test to avoid calculating duration_error for audio streams (see patch below). As far as I could test this reduced the time spent in av_find_stream_info() greatly.

For video streams there is still a good deal of time spent updating duration_error, due to the lack of FPU and the large amount of standard timebases tested when updating duration_error. Is it really necessary to have all those standard time bases? There are currently 725. As far as I understand all frame rates between 1/1001 and 60/1001, in steps of 1/12, are included. Can this be reduced to a (much) more reduced set so that it does not take that much time to compute duration_error? As this code affects all file formats and broken files I do not know all the implications by far...

--- libavformat/utils.c (revision 11006)
+++ libavformat/utils.c (working copy)
@@ -1852,7 +1852,9 @@
         if (pkt->duration != 0)
             codec_info_nb_frames[st->index]++;

-        {
+       /* NOTE: the duration_error calculated here is only required
+        * for video streams, avoid doing it for non-video streams */
+        if (ic->streams[pkt->stream_index]->codec->codec_type == CODEC_TYPE_VIDEO) {
             int index= pkt->stream_index;
             int64_t last= last_dts[index];
             int64_t duration= pkt->dts - last;
@@ -1874,15 +1876,15 @@
             }
             if(last == AV_NOPTS_VALUE || duration_count[index]<=1)
                 last_dts[pkt->stream_index]= pkt->dts;
+       }
+       if (st->codec->codec_id == CODEC_ID_NONE) {
+           AVProbeData *pd = &(probe_data[st->index]);
+           pd->buf = av_realloc(pd->buf, pd->buf_size+pkt->size+AVPROBE_PADDING_SIZE);
+           memcpy(pd->buf+pd->buf_size, pkt->data, pkt->size);
+           pd->buf_size += pkt->size;
+           memset(pd->buf+pd->buf_size, 0, AVPROBE_PADDING_SIZE);
+       }

-            if (st->codec->codec_id == CODEC_ID_NONE) {
-                AVProbeData *pd = &(probe_data[st->index]);
-                pd->buf = av_realloc(pd->buf, pd->buf_size+pkt->size+AVPROBE_PADDING_SIZE);
-                memcpy(pd->buf+pd->buf_size, pkt->data, pkt->size);
-                pd->buf_size += pkt->size;
-                memset(pd->buf+pd->buf_size, 0, AVPROBE_PADDING_SIZE);
-            }
-        }
         if(st->parser && st->parser->parser->split && !st->codec->extradata){
             int i= st->parser->parser->split(st->codec, pkt->data, pkt->size);
             if(i){

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Diego Santa Cruz, PhD
Software Architect, SpinetiX S.A.

PSE-C, CH-1015, Lausanne, Switzerland
Tel:??? +41 (0) 21 693 89 81
Mail:?? Diego.SantaCruz at spinetix.com

Get Information : www.spinetix.com

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