GCP Transcoder API用preset/web-hd建作业时添加PubSub Destination

• 基于GCP Transcoder API处理签名URL上传至Cloud Storage的视频转码，已配置存储桶写入触发的Cloud Function，核心转码流程运行正常，需要新增转码完成后的通知推送能力。
• 参考社区MP4转HLS方案编写基于预设创建转码作业的代码，尝试配置PubsubDestination指向指定Pub/Sub主题接收转码完成通知，但对应配置片段始终无法生效。
• 已查阅Transcoder API Pub/Sub配置官方文档及社区相关解答，未找到可行解决方案。

def create_job_from_preset(project_id, location, input_uri, output_uri, preset):
    """Creates a job based on a job preset.

    Args:
        project_id: The GCP project ID.
        location: The location to start the job in.
        input_uri: Uri of the video in the Cloud Storage bucket.
        output_uri: Uri of the video output folder in the Cloud Storage bucket.
        preset: The preset template (for example, 'preset/web-hd')."""

    client = TranscoderServiceClient()

    parent = f"projects/{project_id}/locations/{location}"
    job = transcoder_v1.types.Job()
    job.input_uri = input_uri
    job.output_uri = output_uri
    job.template_id = preset
    job.ttl_after_completion_days = 1
    job.config = transcoder_v1.types.JobConfig(
        PubsubDestination={
            topic_name=f"projects/{project_id}/topics/testing"
        }
    )
    response = client.create_job(parent=parent, job=job)
    print(f"Job: {response.name}")
    return response

job.config = transcoder_v1.types.JobConfig(
    PubsubDestination={
        topic_name=f"projects/{project_id}/topics/testing"
    }
)

配置不生效有三个核心问题：

1. 字段使用错误：JobConfig中配置Pub/Sub目标的字段为蛇形命名的pubsub_destinations，类型是PubsubDestination对象列表，不是直接传入PubsubDestination字典参数；且PubsubDestination对象中指定主题的字段为topic，不是topic_name。
2. 配置逻辑冲突：使用template_id指定预设模板创建作业时，直接给job.config赋值会完全覆盖预设模板内置的所有转码规则，不仅通知配置无法生效，转码作业本身也会因为缺少必要的转码参数运行异常。
3. 权限未配置：Transcoder服务账号默认没有指定Pub/Sub主题的发布权限，就算参数配置正确也无法推送通知。

1. 先拉取指定预设模板的完整配置，在模板配置基础上追加Pub/Sub通知配置，避免覆盖原有转码规则。
2. 使用正确的字段名和参数类型传入Pub/Sub配置。
3. 给Transcoder服务账号绑定目标Pub/Sub主题的发布权限。

修复后的可运行代码：

def create_job_from_preset(project_id, project_number, location, input_uri, output_uri, preset):
    """Creates a job based on a job preset.

    Args:
        project_id: The GCP project ID.
        project_number: The GCP project number.
        location: The location to start the job in.
        input_uri: Uri of the video in the Cloud Storage bucket.
        output_uri: Uri of the video output folder in the Cloud Storage bucket.
        preset: The preset template (for example, 'preset/web-hd')."""

    client = TranscoderServiceClient()

    parent = f"projects/{project_id}/locations/{location}"
    # 获取预设模板的完整配置，自定义预设直接替换模板名称拼接逻辑即可
    preset_id = preset.replace("preset/", "")
    template_name = f"projects/{project_id}/locations/{location}/jobTemplates/{preset_id}"
    template_config = client.get_job_template(name=template_name).config

    job = transcoder_v1.types.Job()
    job.input_uri = input_uri
    job.output_uri = output_uri
    job.ttl_after_completion_days = 1

    # 基于模板配置追加Pub/Sub通知，不覆盖原有转码规则
    job.config = template_config
    pubsub_target = transcoder_v1.types.PubsubDestination(
        topic=f"projects/{project_id}/topics/testing"
    )
    job.config.pubsub_destinations.append(pubsub_target)

    response = client.create_job(parent=parent, job=job)
    print(f"Job: {response.name}")
    return response

权限配置说明 #

提前给Transcoder官方服务账号service-{project_number}@gcp-sa-transcoder.iam.gserviceaccount.com绑定目标主题的pubsub.publisher角色，否则通知会推送失败。

内容的提问来源于stack exchange，提问作者Mrcreamio