Retrieve Video Frame Rate

[SuspiciousDuck]

I want to seek to a specific frame and decode only that frame. I have the seeking part done, however, a packet does not contain only one frame. I should be able to get the pts of the frame decoded and compare it with a generated pts to make sure it's the right frame, but it appears I can't get the frame rate?

[operutka]

I'm not really sure how exactly you're doing what you just described and I'm also not sure how frame rate fits to it all. So I can't really tell if your approach is correct or if there's anything wrong with your solution. If you need help here, a code snippet with a description saying what exactly it's supposed to do and what doesn't work would be helpful.

Now regarding a few things that you mentioned:

• Decoding a specific frame isn't an easy task. It's highly dependent on the video codec. Take H.264 for example. Most of the frames depend on other frames and cannot be decoded directly. You'd need to seek to the first IDR frame preceding the frame you'd like to decode and then decode everything until you get the frame you want.
• Usually, you can't get any frame rate information from media containers because the actual video frame rate may vary during the entire duration of a video track. You may estimate it (e.g. by calculating an average frame rate) but you probably don't need it. If you just need to be able to tell the exact presentation time of a frame, you need the decoder time base. For convenience, the correct time base is already a part of the Timestamp struct.

[SuspiciousDuck]

I've since moved back to ffmpeg-next (it was what i started with, but the seek() method wasnt working). In this issue, I wanted to calculate a PTS (presentation time stamp) for a frame number by dividing by the frame rate, and multiplying by the time base, then use the PTS and the frame PTS to make sure I retrieved the right frame.
Here's a code snippet using ffmpeg-next to show what I wanted.

for (stream, packet) in demuxed.packets() {
    let pts = packet.pts().unwrap_or(-1);
    if stream.index() != index {
        continue;
    }
    decoder.send_packet(&packet).map_err(|e| e.to_string())?;
    while decoder.receive_frame(&mut decoded).is_ok() {
        let rounded_pts = (decoded.pts().unwrap_or(pts) as f64).round() / 1000f64;
        let rounded_target = (frame as f64 / fps * 1000f64).round() / 1000f64;
        if rounded_target <= rounded_pts {
            scaler
                .run(&decoded, &mut scaled)
                .map_err(|e| e.to_string())?;
            break;
        }
    }
}

[niklaskorz]

Might be solved by #87