如何从任意视频URL获取视频格式（不限于AVPlayer兼容格式）以优化播放器选择与FFmpeg编码逻辑

Great question—let’s break this down into actionable steps to refine your workflow, from reliably detecting video formats to optimizing both player choice and FFmpeg performance.

1. Reliably Detect Video Format (and Metadata) #

Checking AVAsset.isPlayable works, but it’s a blunt tool—you can get far more actionable info by digging into the asset’s track details and format descriptions. Here’s how to extract the actual video format (and extra metadata) without relying solely on URL extensions (which are often missing or misleading):

Swift Code to Fetch Format & Metadata #

import AVFoundation

// Helper struct to hold useful video metadata
struct VideoMetadata {
    let format: String
    let resolution: CGSize
    let frameRate: Float
    let duration: Double
}

func fetchVideoMetadata(from url: URL, completion: @escaping (VideoMetadata?) -> Void) {
    let asset = AVAsset(url: url)
    let keysToLoad = ["tracks", "duration"]
    
    asset.loadValuesAsynchronously(forKeys: keysToLoad) {
        var loadError: NSError?
        let tracksStatus = asset.statusOfValue(forKey: "tracks", error: &loadError)
        let durationStatus = asset.statusOfValue(forKey: "duration", error: &loadError)
        
        guard tracksStatus == .loaded && durationStatus == .loaded else {
            completion(nil)
            return
        }
        
        guard let videoTrack = asset.tracks(withMediaType: .video).first else {
            completion(nil)
            return
        }
        
        // Extract codec type and map to user-friendly format
        guard let formatDesc = videoTrack.formatDescriptions.first as? CMVideoFormatDescription else {
            completion(nil)
            return
        }
        let codecType = CMVideoFormatDescriptionGetCodecType(formatDesc).stringValue.lowercased()
        let videoFormat = mapCodecToReadableFormat(codecType)
        
        // Extract additional metadata
        let resolution = videoTrack.naturalSize
        let frameRate = videoTrack.nominalFrameRate
        let duration = CMTimeGetSeconds(asset.duration)
        
        completion(VideoMetadata(
            format: videoFormat,
            resolution: resolution,
            frameRate: frameRate,
            duration: duration
        ))
    }
}

private func mapCodecToReadableFormat(_ codecType: String) -> String {
    switch codecType {
    case "avc1", "avc3":
        return "MP4 (H.264)"
    case "hvc1", "hev1":
        return "MP4 (HEVC/H.265)"
    case "mpeg1", "mpeg2":
        return "MPEG"
    case "av01":
        return "AV1"
    case "hls", "mpegurl":
        return "M3U8 (HLS)"
    case "flv1":
        return "FLV"
    // Add more mappings for codecs you encounter
    default:
        return codecType.capitalized
    }
}

This approach gives you precise format info (not just a guess from the URL) plus key metadata that’ll supercharge your FFmpeg workflow later.

2. Refine Player Selection Logic #

With the format in hand, you can make smarter decisions than waiting for isPlayable:

• Use AVPlayer by default for formats it natively supports: MP4 (H.264/HEVC), M3U8 (HLS), MOV, etc.
• Switch to a third-party player (like ijkplayer) for formats AVPlayer struggles with (e.g., FLV, some niche MPEG variants) or if you need advanced features (like custom DRM handling).
• Skip AVPlayer entirely for known unsupported formats—no need to waste time loading the asset just to find out it’s unplayable.

If you still want to keep isPlayable as a fallback (for edge cases like corrupted MP4s), combine it with format info:

func decidePlayer(for url: URL, completion: @escaping (PlayerType) -> Void) {
    fetchVideoMetadata(from: url) { metadata in
        guard let format = metadata?.format else {
            // Fallback to checking isPlayable if metadata fetch fails
            let asset = AVAsset(url: url)
            asset.loadValuesAsynchronously(forKeys: ["playable"]) {
                let isPlayable = asset.isPlayable
                completion(isPlayable ? .avPlayer : .ffmpegTranscode)
            }
            return
        }
        
        switch format {
        case "MP4 (H.264)", "MP4 (HEVC/H.265)", "M3U8 (HLS)":
            // Verify AVPlayer can play it (for edge cases)
            let asset = AVAsset(url: url)
            asset.loadValuesAsynchronously(forKeys: ["playable"]) {
                completion(asset.isPlayable ? .avPlayer : .ffmpegTranscode)
            }
        case "FLV", "MPEG":
            completion(.thirdPartyPlayer) // Or jump straight to FFmpeg if needed
        default:
            completion(.ffmpegTranscode)
        }
    }
}

enum PlayerType {
    case avPlayer
    case thirdPartyPlayer
    case ffmpegTranscode
}

3. Optimize FFmpeg Transcoding with Metadata #

Now that you have the format, resolution, frame rate, etc., you can tailor FFmpeg commands to get better quality, faster speeds, or smaller file sizes. Here are examples of how to leverage the metadata:

Example 1: Transcoding an M3U8 to MP4 #

If the source is HLS (M3U8), you can skip unnecessary format conversions and use FFmpeg’s native HLS support:

ffmpeg -i input.m3u8 -c:v libx264 -preset medium -crf 23 -c:a aac -b:a 128k output.mp4

Example 2: Downscaling a High-Res Video #

If the metadata shows a 4K video but you need 1080p output, add resolution scaling:

ffmpeg -i input.mp4 -c:v libx264 -preset fast -crf 25 -s 1920x1080 -c:a copy output.mp4

Example 3: Handling MPEG Files #

For MPEG sources, you can either transcode to MP4 or optimize the MPEG output:

# Transcode MPEG to MP4
ffmpeg -i input.mpeg -c:v libx264 -preset slow -crf 22 -c:a aac output.mp4

# Optimize existing MPEG (reduce file size without re-encoding video)
ffmpeg -i input.mpeg -c:v copy -c:a mp3 -q:a 2 output_optimized.mpeg

The key is matching FFmpeg’s codec and filter parameters to the source format—this avoids wasted processing and ensures the output fits your app’s needs perfectly.

内容的提问来源于stack exchange，提问作者Bruno Pantaleão