feat(media_publish): per-track bitrate + codec-aware encoder options

[rickstaa]

Problem

The trickle output path (MediaPublish / VideoOutputConfig) had two limits:

1. No bitrate. VideoOutputConfig has no bitrate field, so a rendition ladder can't set per-tier bitrates — the encoder picks its own default. That makes the output unpredictable and unusable for real ABR.
2. x264-only. The encoder options were hardcoded for libx264 (preset=superfast, tune=zerolatency, forced-idr, bf) and applied to every codec, so libsvtav1 / libvpx-vp9 / *_nvenc fail at avcodec_open2 with Invalid argument.

Change

VideoOutputConfig gains three optional, backward-compatible fields:

• bit_rate — target average video bitrate (bits/sec)
• profile — H.264/H.265 profile ("high", "main", "baseline"); codecs without one ignore it
• encoder_options — extra ffmpeg options merged over the per-codec defaults

Encoder options are now codec-aware (_encoder_base_options): x264/x265 keep the original low-latency set (identical behavior), other codecs start empty so they open cleanly, and callers tune via encoder_options (e.g. {"preset":"p4","tune":"ll"} for av1_nvenc). bit_rate is applied to the stream's codec context after add_stream.

Result

Unlocks bitrate control and AV1/HEVC/VP9 on the live/trickle transcode path in one change. Defaults are unchanged — existing libx264 callers see no difference.

Tests

tests/test_media_publish_encoder.py — x264 keeps its options, non-x264 get empty base options, and the new fields default to no-op / are accepted. 4 passed.

Follow-ups (not in this PR)

• Per-codec low-latency defaults for non-x264 (kept empty here to guarantee avcodec_open2 succeeds; opt in via encoder_options).
• Explicit gop_size from keyframe_interval_s (segmentation currently drives keyframes).

🤖 Generated with Claude Code

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