.net-core获取ffmpeg转码进度及剩余时间

2019-02-02

.NET Core

> ffmpeg虽然可以转码，但是从默认的输出信息无法看出转码进度及剩余时间

# ffmpeg的转码输出信息

ffmpeg 转码的过程中输出的信息，无法直接获取当前转码的进度，一个示例的输出如下：

    frame= 1777 fps=108 q=40.0 Lsize=    1954kB time=00:04:55.89 bitrate=  54.1kbits/s dup=0 drop=4141 speed=17.9x
    frame=16788 fps=108 q=40.0 size=    1536kB time=00:04:39.38 bitrate=  45.0kbits/s dup=0 drop=3907 speed=  18x    

# 如何获取转码进度？

从如上的输出信息可以发现，可以从两个方面获取进度：

* frame
* time

对应的进度计算公式如下：

* 1 - (total_frame - frame) / total_frame
* time / duration

## 如何获取总帧数和持续时间

可以通过ffprobe工具来获取视频信息

    ffprobe -v quiet -print_format json -show_format -show_streams [video file]

输出的结果类似：

```json
{
    "streams": [
        {
            "index": 0,
            "codec_name": "aac",
            "codec_long_name": "AAC (Advanced Audio Coding)",
            "profile": "LC",
            "codec_type": "audio",
            "codec_time_base": "1/44100",
            "codec_tag_string": "mp4a",
            "codec_tag": "0x6134706d",
            "sample_fmt": "fltp",
            "sample_rate": "44100",
            "channels": 2,
            "channel_layout": "stereo",
            "bits_per_sample": 0,
            "r_frame_rate": "0/0",
            "avg_frame_rate": "0/0",
            "time_base": "1/44100",
            "start_pts": 0,
            "start_time": "0.000000",
            "duration_ts": 102390024,
            "duration": "2321.769252",
            "bit_rate": "141914",
            "max_bit_rate": "236004",
            "nb_frames": "100088",
            "disposition": {
                "default": 1,
                "dub": 0,
                "original": 0,
                "comment": 0,
                "lyrics": 0,
                "karaoke": 0,
                "forced": 0,
                "hearing_impaired": 0,
                "visual_impaired": 0,
                "clean_effects": 0,
                "attached_pic": 0,
                "timed_thumbnails": 0
            },
            "tags": {
                "creation_time": "2018-04-25T11:29:17.000000Z",
                "language": "eng",
                "handler_name": "Mainconcept MP4 Sound Media Handler"
            }
        },
        {
            "index": 1,
            "codec_name": "h264",
            "codec_long_name": "H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
            "profile": "High",
            "codec_type": "video",
            "codec_time_base": "46480601/1859160000",
            "codec_tag_string": "avc1",
            "codec_tag": "0x31637661",
            "width": 1364,
            "height": 768,
            "coded_width": 1376,
            "coded_height": 768,
            "has_b_frames": 1,
            "sample_aspect_ratio": "1024:1023",
            "display_aspect_ratio": "16:9",
            "pix_fmt": "yuv420p",
            "level": 32,
            "color_range": "tv",
            "color_space": "bt709",
            "color_transfer": "bt709",
            "color_primaries": "bt709",
            "chroma_location": "left",
            "refs": 1,
            "is_avc": "true",
            "nal_length_size": "4",
            "r_frame_rate": "20/1",
            "avg_frame_rate": "929580000/46480601",
            "time_base": "1/20000",
            "start_pts": 1000,
            "start_time": "0.050000",
            "duration_ts": 46479000,
            "duration": "2323.950000",
            "bit_rate": "413761",
            "bits_per_raw_sample": "8",
            "nb_frames": "46479",
            "disposition": {
                "default": 1,
                "dub": 0,
                "original": 0,
                "comment": 0,
                "lyrics": 0,
                "karaoke": 0,
                "forced": 0,
                "hearing_impaired": 0,
                "visual_impaired": 0,
                "clean_effects": 0,
                "attached_pic": 0,
                "timed_thumbnails": 0
            },
            "tags": {
                "creation_time": "2018-04-25T11:29:17.000000Z",
                "language": "eng",
                "handler_name": "Mainconcept MP4 Video Media Handler",
                "encoder": "AVC Coding"
            }
        }
    ],
    "format": {
        "filename": "3.mp4",
        "nb_streams": 2,
        "nb_programs": 0,
        "format_name": "mov,mp4,m4a,3gp,3g2,mj2",
        "format_long_name": "QuickTime / MOV",
        "start_time": "0.000000",
        "duration": "2323.950000",
        "size": "162498216",
        "bit_rate": "559386",
        "probe_score": 100,
        "tags": {
            "major_brand": "mp42",
            "minor_version": "0",
            "compatible_brands": "isommp42",
            "creation_time": "2018-04-25T11:29:16.000000Z"
        }
    }
}
```

可以看到，获取总帧数和持续时间的 JSonPath 分别如下：

* $.streams[1].nb_frames
* $.format.duration

用JObject解析JSon示例代码如下：

```c#
var videoFormatObject = JObject.Parse(json);
var durationObject = videoFormatObject.SelectToken("$.format.duration");
var duration = durationObject.Value<double>();
```

# 如何获取转码剩余时间？

虽然从转码进度可以得出转码所需时间，但并不直观，如何直观的显示出剩余时间？

分析ffmpeg转码时的输出发现，可以从 time, speed, duration 这3个数据计算出转码剩余时间：

    剩余时间 = (duration - timeTranscoded) / speed

代码示例如下：

```c#
var transcodeLog = "frame= 1777 fps=108 q=40.0 Lsize=    1954kB time=00:04:55.89 bitrate=  54.1kbits/s dup=0 drop=4141 speed=17.9x";
var match = Regex.Match(transcodeLog, "time=(\\S+)");
if (match.Success)
{
    var timeTranscoded = TimeSpan.Parse(match.Groups[1].Value).TotalSeconds;
    // Trim() remove space when speed=  18x
    speed = Convert.ToDouble(Regex.Match(transcodeLog, "speed=(.+)x").Groups[1].Value.Trim());
    Console.WriteLine($"Percentage: {(timeTranscoded / duration).ToString("p")}, Remaining time: {((duration - timeTranscoded) / speed).ToString("f1")}s");
}
```

# 如何调用进程并持续获取进程的输出？

调用进程时，需要设定 StartInfo.Redirect... = true，并监听数据接收事件，示例代码如下：

```c#
string param = $"-y -i [input video] -vcodec libx264 -vf scale=1280:720 -r 6 -crf 40 -acodec aac -q:a 0.4 -ac 1 [output video]";
using (Process p = new Process())
{
    p.StartInfo.FileName = "ffmpeg.exe";
    p.StartInfo.Arguments = param;
    p.StartInfo.UseShellExecute = false;
    p.StartInfo.RedirectStandardOutput = true;
    p.StartInfo.RedirectStandardError = true;
    var output = new DataReceivedEventHandler((sender, e) =>
    {
        if (!String.IsNullOrEmpty(e.Data))
        {
            Console.WriteLine(e.Data);
        }
    });
    p.OutputDataReceived += output;
    p.ErrorDataReceived += output;

    p.Start();
    p.BeginOutputReadLine();
    p.BeginErrorReadLine(); // ffmpeg的进度输出是通过 Error 管道
    p.WaitForExit();
}
```

完成之后的转码进度及剩余时间显示：

    Percentage: 2.37 %, Remaining time: 21.7s
    Percentage: 5.40 %, Remaining time: 18.1s
    Percentage: 8.44 %, Remaining time: 16.6s
    ...
    Percentage: 96.83 %, Remaining time: 0.5s
    Percentage: 99.87 %, Remaining time: 0.0s
    Percentage: 100.00 %, Remaining time: 0.0s

# 参考：

* [ffmpeg libx264编码介绍](https://trac.ffmpeg.org/wiki/Encode/H.264)
* [ffmpeg aac编码介绍](https://trac.ffmpeg.org/wiki/Encode/AAC)
* [ffmpeg Documentation](https://ffmpeg.org/ffmpeg.html)

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