Intelligent Media Services:Best practices for multi-subtitle transcoding and packaging

Configuration workflow

The following flowchart shows the configuration workflow for transcoding templates.

Sample requirements

This example uses the following requirements:

• Encoding protocol — H264 or H265

• Video resolution — 360P, 540P, 720P, or 1080P

• Audio — HE-AAC at 64 Kbps. Other audio parameters use default values.

• Subtitles — M3U8 (VTT)

Configuration example

This example uses four video quality levels. Create the video transcoding templates as described in the following tables. For more information, see Create a transcoding template.

The job example in this topic also references an audio transcoding template named Audio-64Kbps for the HE-AAC audio outputs. Make sure that this template is created before you submit the packaging job.

To use Narrowband HD transcoding, create the corresponding templates as described in the tables, and then submit a ticket. Alibaba Cloud then upgrades the configuration in the backend.

The following tables describe the templates for the H264 and H265 encoding protocols. If you use H265, review the following container format considerations:

• Preferred option — Use the fmp4 container format. It is the Apple standard protocol and works well with the Safari browser.

• Alternative — The ts container format also works, but it is not compatible with Safari.

• Console limitation — You cannot create the fmp4 container format in the console. Create the template with the m3u8(ts) container format first. Alibaba Cloud then upgrades the configuration in the backend.

Use OverrideParams to set subtitle streams

You cannot customize subtitle information in a transcoding template. To configure subtitle streams, explicitly set the subtitle information with OverrideParams when you submit the job. The following tables describe the subtitle stream settings.

Subtitles

Subtitle

Config description (HlsGroupConfig)

Each output in the job example contains an HlsGroupConfig object that describes the output stream in the HLS manifest. The following table describes the parameters.

Example: transcode and generate multi-bitrate packaged files

The following example defines four inputs: a video (video), an English audio track (EnglishAudio), a Chinese subtitle track (ChineseSubtitle), and an English subtitle track (EnglishSubtitle). The outputs include two video quality levels (720P and 360P), two audio tracks, and two subtitle tracks. This example uses two of the four video templates that you created. You can add or remove video outputs as needed.

Each output, including each subtitle output, requires a TemplateId. For a subtitle output, specify the ID of any transcoding template in the packaging job. In the following example, replace <TemplateId> with an existing template ID, such as Video-360P.

The following JSON corresponds to the Config parameter of the SubmitMediaConvertJob request. Replace the angle-bracket placeholders with your actual values.

{
    "Config": {
        "Inputs": [
            {
                "Name": "video",
                "InputFile": {
                    "Type": "OSS",
                    "Url": "https://<Bucket>.<OSSPublicEndpoint>/<Video1Chinese>"
                }
            },
            {
                "Name": "EnglishAudio",
                "InputFile": {
                    "Type": "OSS",
                    "Url": "https://<Bucket>.<OSSPublicEndpoint>/<Audio1English>"
                }
            },
            {
                "Name": "ChineseSubtitle",
                "InputFile": {
                    "Type": "OSS",
                    "Url": "https://<Bucket>.<OSSPublicEndpoint>/<Subtitle1Chinese>"
                }
            },
            {
                "Name": "EnglishSubtitle",
                "InputFile": {
                    "Type": "OSS",
                    "Url": "https://<Bucket>.<OSSPublicEndpoint>/<Subtitle1English>"
                }
            }
        ],
        "OutputGroups": [
            {
                "Name": "Hls",
                "GroupConfig": {
                    "Type": "Hls",
                    "OutputFileBase": {
                        "Type": "OSS",
                        "Url": "https://<Bucket>.<PublicEndpoint>/<URI>/"
                    },
                    "ManifestName": "<m3u8filename>"
                },
                "Outputs": [
                    {
                        "Name": "720P",
                        "OutputFileName": "video/720p/720p",
                        "TemplateId": "Video-720P",
                        "HlsGroupConfig": {
                            "Type": "Video"
                        }
                    },
                    {
                        "Name": "360P",
                        "OutputFileName": "video/360p/360p",
                        "TemplateId": "Video-360P",
                        "HlsGroupConfig": {
                            "Type": "Video"
                        }
                    },
                    {
                        "OutputFileName": "audio/chinese/chinese",
                        "TemplateId": "Audio-64Kbps",
                        "HlsGroupConfig": {
                            "Type": "Audio",
                            "Name": "ChineseAudio",
                            "Language": "zh",
                            "Autoselect": "TRUE",
                            "Default": "TRUE"
                        }
                    },
                    {
                        "InputRef": "ChineseSubtitle",
                        "OutputFileName": "subtitle/chinese/chinese",
                        "TemplateId": "<TemplateId>",
                        "OverrideParams": {
                            "Subtitles": [
                                {
                                    "Codec": "vtt"
                                }
                            ]
                        },
                        "HlsGroupConfig": {
                            "Type": "Subtitle",
                            "Name": "ChineseSubtitle",
                            "Language": "zh",
                            "Autoselect": "TRUE",
                            "Default": "TRUE"
                        }
                    },
                    {
                        "InputRef": "EnglishAudio",
                        "OutputFileName": "audio/english/english",
                        "TemplateId": "Audio-64Kbps",
                        "HlsGroupConfig": {
                            "Type": "Audio",
                            "Name": "EnglishAudio",
                            "Language": "en",
                            "Autoselect": "TRUE",
                            "Default": "FALSE"
                        }
                    },
                    {
                        "InputRef": "EnglishSubtitle",
                        "OutputFileName": "subtitle/english/english",
                        "TemplateId": "<TemplateId>",
                        "OverrideParams": {
                            "Subtitles": [
                                {
                                    "Codec": "vtt"
                                }
                            ]
                        },
                        "HlsGroupConfig": {
                            "Type": "Subtitle",
                            "Name": "EnglishSubtitle",
                            "Language": "en",
                            "Autoselect": "TRUE",
                            "Default": "FALSE"
                        }
                    }
                ]
            }
        ]
    }
}

Callback event

When a packaging job completes, IMS sends a callback event. The event type (EventType) is MediaConvertComplete. The console does not yet support selecting this event. To configure it, call the SetEventCallback operation.

Key field description

The following table describes the key fields of the callback event.

The following example shows a callback event:

{
    "FinishTime": "2025-05-09T08:03:21Z",
    "JobId": "your-job-id",
    "Status": "Success",
    "TriggerSource": "IceWorkflow",
    "UserData": "{\"ImsSrc\":\"Workflow\",\"TaskId\":\"e89a955d88ca47f0b9b79c562e5c622f\"}"
}