Engines

Downloaders are the core of the application. They are responsible for downloading the video stream from the source. The application supports three downloaders: Mesio, FFMPEG, and Streamlink. Each downloader has its own features and limitations.

TIP

For Mesio users, it is highly recommended to enable both FLV Consistency Fix and HLS Consistency Fix. These pipelines correct or isolate timestamp and stream-structure changes so one bad transition is less likely to make the rest of a recording undecodable. Media that the source never delivered cannot be recovered.

The FFMPEG downloader is the default downloader and is the most stable and reliable. It is written in C and is capable of downloading FLV and HLS streams. It provides excellent compatibility for various streaming scenarios, including support for non-standard HEVC in FLV/RTMP containers, and generally has low CPU and memory usage. However, it does not support multithreading for HLS downloads.

NOTE

The FFMPEG version provided in our Docker images is a specialized build from yt-dlp/FFmpeg-Builds. This build is optimized for streaming and includes (or has upstreamed) critical patches for smooth integration with yt-dlp, such as fixing AAC HLS truncation, supporting long paths on Windows, and decoding non-standard HEVC in FLV containers.

1. Engines Feature List

Feature	Mesio	FFMPEG	STREAMLINK
FLV Download	✅	✅	❌
HLS Download	✅ (Multithreaded)	✅	✅ (Multithreaded)
Recording Duration Stats	✅ (Raw data mode not supported)	✅	✅
Download Bitrate Stats	✅	✅ (-f segmentation not supported)	✅ (-f segmentation not supported)
Size Segmentation	✅ (Raw data mode not supported)	✅ (-f segmentation not supported)	✅
Duration Segmentation	✅ (Raw data mode not supported)	✅	✅
Download Format	FLV, M3U8, TS, M4S	Supports other formats	Supports other formats
FLV Consistency Fix	✅ (Recommended)	❌	❌
HLS Consistency Fix	✅ (Recommended)	❌	❌
CPU Usage	Lowest	Low	Low
Memory Usage	Lowest	Low	Medium

2. FLV Consistency Fix

When enabled, FLV items pass through one ordered repair chain before the writer. The chain preserves media payloads while fixing container-level structure:

Concern	Pipeline behavior
Missing FLV header	Insert a valid header before the first tag
Video or audio format change	Start a new output file with the headers required for playback
Out-of-order video data	Reorder nearby tags while keeping memory use bounded
Timestamp jumps or regressions	Adjust timestamps to preserve playback continuity
Duplicate media tags or sequence headers	Filter them when the corresponding option is enabled
File size or duration limit	Rotate on a video keyframe, or on the next tag for audio-only output
FLV statistics and seek index	Update metadata before the file is closed

Metadata updates do not rewrite the completed media data. If the available metadata space fills, the optional seek index is shortened instead. Filtered or encrypted script payloads are left unchanged.

3. Raw Data Mode

Raw Data Mode is a high-performance download mode supported by the Mesio engine. In this mode, the engine writes the stream data directly to the disk as it's received from the network, without parsing or processing the internal media packets (headers, frames, metadata).

Key Characteristics:

• Maximum Performance: Since there is no packet parsing or re-muxing, CPU and memory usage are at their absolute minimum.
• Zero Overhead: Ideal for high-bandwidth streams or resource-constrained environments (like low-end NAS or VPS). Only recommended if the network is stable and the CDN/stream source has no data fluctuations (e.g., media headers changing).

Limitations:

Because the headers and packet structures are not inspected, some advanced features are unavailable when Raw Data Mode is enabled:

• Statistics: Recording duration and bitrate stats cannot be calculated in real-time.
• Segmentation: The engine cannot detect frame boundaries or duration, so it cannot perform precise segmentation by size or duration.
• Repair: Features like FLV Consistency Fix or HLS Consistency Fix cannot be applied as they require packet-level manipulation.

4. HLS Consistency Fix (Mesio Exclusive)

Mesio's HLS download reactor and HLS fix pipeline have separate responsibilities:

• The download engine orders fetched segments, writes required fMP4 initialization data before dependent media, applies the configured gap policy, and preserves playlist discontinuities as output boundaries.
• The consistency fix starts a new output file when delivered segments contain incompatible codec, resolution, program-layout, or fMP4 initialization changes. It also enforces file-size and duration limits.

The pipeline does not rewrite timestamps inside TS or fMP4 payloads, recreate missing media, or transcode codecs. A skipped segment remains an observable gap; the pipeline keeps delivered output ordered and rotates when a detected format change requires a new file.

5. Mesio Architecture

Mesio is an in-process Rust engine with a reactor-based HLS downloader and a unified download-session model shared by HLS and FLV. For the architecture diagram and a walkthrough of how it works under the hood, see the dedicated Mesio Engine page.