libavcodec get video duration and framerate

Question

I have a video encoded in .3gp h.264 and I am looking to get its framerate and duration in C. Here is the code I use after opening the file and finding the appropriate codecs:

AVRational rational = gVideoCodecCtx->time_base;

LOGI(10, "numerator is %i", rational.num);
LOGI(10, "denominator is %i", rational.den);
LOGI(10, "duration is %d", gFormatCtx->duration);
LOGI(10, "fps is %d", (double)av_q2d(rational));

And here is the output:

12-02 12:30:19.819: I/FFmpegTest(23903): numerator is 1
12-02 12:30:19.819: I/FFmpegTest(23903): denominator is 180000
12-02 12:30:19.819: I/FFmpegTest(23903): duration is 6594490
12-02 12:30:19.819: I/FFmpegTest(23903): fps is 1692926992

From the documentation I understand that the duration is meant to be "duration/time_base" which gives me 6594490 / 180000 = 36.6. The duration of my video file is 6 seconds and I do not know where this factor of 6 would come from.

Also the framerate seems to be completely off.

It is currenlty hard to find help as a lot of tutorials use deprecated methods and the documentation does not give examples.

Any help would be appreciated.

Thanks

Edit: Thanks to the comment below I managed to print the following

12-02 18:59:36.279: I/FFmpegTest(435): numerator is 1
12-02 18:59:36.279: I/FFmpegTest(435): denominator is 180000
12-02 18:59:36.279: I/FFmpegTest(435): duration is 6594490
12-02 18:59:36.279: I/FFmpegTest(435): fps is 0.000006

I also managed to find out a frame's timestamp in msec with this:

int msec = 1000*(packet.pts * timeBase * gVideoCodecCtx->ticks_per_frame);

This returns me something that's roughly 33fps (I expect 30). But I can't figure out how to retrieve the duration. The documentation says "duration of the stream, in AV_TIME_BASE fractional seconds" but 6594490 * 0.000006 = 39.5 - the correct duration is 6.3 seconds). Also the exact fps is 30 but nor sure how to get from 0.000006 to 30 with the above figures)

Thanks

Answer 1

FPS can be obtained this way:

const double FPS = (double)videoStream->r_frame_rate.num / (double)videoStream->r_frame_rate.den;

where videoStream is:

AVFormatContext * format = NULL;
if ( avformat_open_input( & format, "my_video.mkv", NULL, NULL ) != 0 ) ) on_error();
if ( avformat_find_stream_info( format, NULL ) < 0) on_error();
//av_dump_format( format, 0, "my_video.mkv", false );
AVCodec * video_dec = (AVCodec*)1;
const auto video_stream_index = av_find_best_stream( format, AVMEDIA_TYPE_VIDEO, -1, -1, & video_dec, 0 );
if ( video_stream_index < 0 ) on_error();
const auto videoStream = format->streams[ video_stream_index ];