emit audio progress events

[nathanbabcock]

TL;DR: audio events will have 0 for unsupported fields. Fixes #81

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This is a quick non-breaking fix, supporting parsing audio progress messages which have a slightly different format than video ones:

Video progress:

[info] frame= 1996 fps=1984 q=-1.0 Lsize=     372kB time=00:01:19.72 bitrate=  38.2kbits/s speed=79.2x

Audio progress:

[info] size=      66kB time=00:00:02.21 bitrate= 245.0kbits/s speed=1.07x

Specifically audio progress omits frame, fps, and q fields.

The most thorough and typesafe fix will be to add a dedicated AudioProgress event type with those fields omitted. That would be a breaking change in conjunction with adding #[non_exhaustive] to support future added event types.

cc @ashhhleyyy fyi

[Copilot]

Pull Request Overview

This PR enables parsing of audio progress events from ffmpeg, which have a different format than video progress events. The key change is making the video-specific fields (frame, fps, and q) optional by defaulting them to 0 when not present, allowing the same parser to handle both audio and video progress messages.

• Modified try_parse_progress function to handle missing video-specific fields
• Added test coverage for audio progress parsing
• Updated documentation to clarify behavior for audio-only events