[Libav-user] [External] Questions about decoding broken streams

Wed Oct 3 17:36:58 EEST 2018

So there is no way to determine decoding errors except parsing log
messages? It smells terrible )
I see only way to detect such green images by analyzing color of decoded
frames, but it can be CPU-intensive

Also of course it's possible to patch some decoders, but It's also not
correct way I guess.

ср, 3 окт. 2018 г. в 13:48, Anton Shekhovtsov <shekh.anton at gmail.com>:

>
>
> ср, 3 окт. 2018 г. в 13:31, Niraj Gandha <niraj.gandha at einfochips.com>:
>
>> Use below code and might help you in solving your problem.
>>
>> while (av_read_frame(refrenceFormatCtx, &packet) >= 0) {
>>
>> if (packet.stream_index == video_stream_index) { //packet is video
>>
>> if (stream == NULL) { //create stream in file
>>
>> stream = avformat_new_stream(output_ctx,
>> refrenceFormatCtx->streams[video_stream_index]->codec->codec);
>>
>> avcodec_copy_context(stream->codec,
>> refrenceFormatCtx->streams[video_stream_index]->codec);
>>
>> stream->sample_aspect_ratio =
>> refrenceFormatCtx->streams[video_stream_index]->codec->sample_aspect_ratio;
>>
>> }
>> int check = 0;
>>  packet.stream_index = stream->id;
>> int result = avcodec_decode_video2(codec_ctx, picture_yuv, &check,
>> &packet);
>>
>> av_free_packet(&packet);
>>
>> av_packet_unref(&packet);
>>
>> if(result <= 0 || check == 0){
>>
>> continue;
>>
>> }
>>
>> if(initialize_rgb_requirements) {
>>
>> sizeofrgbpicture = avpicture_get_size(AV_PIX_FMT_RGB24, codec_ctx->width,
>> codec_ctx->height);
>>
>> picture_rgb = av_frame_alloc();
>>
>> picture_buffer_rgb = (uint8_t*) (av_malloc(sizeofrgbpicture));
>>
>> avpicture_fill((AVPicture *) picture_rgb, picture_buffer_rgb,
>> AV_PIX_FMT_RGB24, codec_ctx->width, codec_ctx->height);
>>
>> img_convert_ctx = sws_getContext(codec_ctx->width, codec_ctx->height,
>> AV_PIX_FMT_YUV420P, codec_ctx->width, codec_ctx->height,AV_PIX_FMT_RGB24,
>> SWS_BICUBIC, NULL, NULL, NULL);
>> initialize_rgb_requirements=0;
>>
>> }
>>
>> int height = 0;
>>
>> if(picture_yuv->data != NULL) {
>> height = sws_scale(img_convert_ctx, ((AVPicture*)picture_yuv)->data,
>> ((AVPicture*)picture_yuv)->linesize, 0, codec_ctx->height,
>> ((AVPicture*)picture_rgb)->data,((AVPicture*)picture_rgb)->linesize);
>>
>> }
>>
>> rgb_image_data = (uint8_t *)malloc(sizeofrgbpicture * sizeof(uint8_t));
>>
>> int ret = avpicture_layout((AVPicture *)picture_rgb, AV_PIX_FMT_RGB24,
>> codec_ctx->width, codec_ctx->height, rgb_image_data, sizeofrgbpicture);
>>
>> emit imageQueued(rgb_image_data, codec_ctx->width,codec_ctx->height);
>>
>> }
>> }
>>
>> Get Outlook for Android <https://aka.ms/ghei36>
>>
>> ------------------------------
>> *From:* Libav-user <libav-user-bounces at ffmpeg.org> on behalf of Vasiliy
>> Volkov <volk.vasiliy at gmail.com>
>> *Sent:* Wednesday, October 3, 2018 3:44:49 PM
>> *To:* libav-user at ffmpeg.org
>> *Subject:* Re: [Libav-user] [External] Questions about decoding broken
>> streams
>>
>> Well there is no anything unusual in our code. We're simply use this API:
>> https://ffmpeg.org/doxygen/4.0/group__lavc__encdec.html
>>
>> avcodec_send_packet
>> avcodec_receive_frame
>>
>> And for context we setup:
>> context->err_recognition = AV_EF_EXPLODE | AV_EF_BITSTREAM | AV_EF_BUFFER
>> | AV_EF_CAREFUL | AV_EF_COMPLIANT | AV_EF_AGGRESSIVE;
>>
>>
>> ср, 3 окт. 2018 г. в 12:58, Niraj Gandha <niraj.gandha at einfochips.com>:
>>
>>> Hi Vasiliy,
>>>
>>> Can you share the code in which you are decoding the stream?
>>>
>>> Thanks,
>>> Niraj Gandha
>>>
>>> Get Outlook for Android <https://aka.ms/ghei36>
>>>
>>> ------------------------------
>>> *From:* Libav-user <libav-user-bounces at ffmpeg.org> on behalf of Vasiliy
>>> Volkov <volk.vasiliy at gmail.com>
>>> *Sent:* Wednesday, October 3, 2018 3:08:08 PM
>>> *To:* libav-user at ffmpeg.org
>>> *Subject:* [External] [Libav-user] Questions about decoding broken
>>> streams
>>>
>>> CAUTION: This email originated from outside of the organization. Do not
>>> click links or open attachments unless you recognize the sender and know
>>> the content is safe.
>>>
>>> Hi,
>>>
>>> I'm trying to deal with broken streams with libav. Sometimes streams can
>>> be broken due to nature of incoming network channel (UDP multicast) but i'd
>>> like to "fix them" as much as possible. I'm trying to fill broken frames
>>> with last good decoded frame. There are situations when I can do such thing
>>> and everything is ok but most of time it's not helping: libav tries to
>>> decode broken stream and add some green frames (h264 decoding) which really
>>> catch your eyes when you watch this stream after encoding.
>>> Is it possible to change this color to black for example? Can libav
>>> while decoding set some flags to frames and mark them as broken or "green"?
>>> It will be helpful because next I'll can replace such frames with
>>> correctly decoded which fix it.
>>>
>>> Thanks
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>
>
> What you wanted to show with this example? That's true, some (or all)
> decoders don't return errors.
> Example in ffv1dec.c
>                 av_log(f->avctx, AV_LOG_ERROR, "CRC mismatch %X!", crc);
> No error code returned from here. It is possible to abuse log hook somehow.
>
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