id	summary	reporter	owner	description	type	status	priority	component	version	resolution	keywords	cc	blockedby	blocking	reproduced	analyzed
1831	Seeking by byte returns success but does not seek	mbradshaw		"'''Summary of the bug:'''
When calling `av_seek_frame()` (or `avformat_seek_file()`) with `AVSEEK_FLAG_BYTE`, it returns 0 indicating success, however, the seek is not performed. I have attached a file that exposes this failure, though I have many files for which this problem occurs.

'''How to reproduce:'''
I created the below quick sample code to show that seeking by byte does not work. If you change the seeking flag to `AVSEEK_FLAG_BACKWARD` then it works as expected. In both cases, however, `av_seek_frame()` returns 0, indicating success.
{{{
#include <iostream>

extern ""C""
{
#include <avcodec.h>
#include <avformat.h>
#include <swscale.h>
};

int main()
{
    av_register_all();

    AVFrame* frame = avcodec_alloc_frame();
    if (!frame)
    {
        std::cout << ""Error allocating the frame"" << std::endl;
        return 1;
    }

    AVFormatContext* formatContext = NULL;
    if (avformat_open_input(&formatContext, ""C:/Users/mbradshaw/Desktop/b/MP4-MC264-AAC.mp4"", NULL, NULL) != 0)
    {
        av_free(frame);
        std::cout << ""Error opening the file"" << std::endl;
        return 1;
    }

    if (avformat_find_stream_info(formatContext, NULL) < 0)
    {
        av_free(frame);
        av_close_input_file(formatContext);
        std::cout << ""Error finding the stream info"" << std::endl;
        return 1;
    }

    AVStream* audioStream = NULL;
    for (unsigned int i = 0; i < formatContext->nb_streams; ++i)
    {
        if (formatContext->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO)
        {
            audioStream = formatContext->streams[i];
            break;
        }
    }

    if (audioStream == NULL)
    {
        av_free(frame);
        av_close_input_file(formatContext);
        std::cout << ""Could not find any audio stream in the file"" << std::endl;
        return 1;
    }

    AVCodecContext* codecContext = audioStream->codec;

    codecContext->codec = avcodec_find_decoder(codecContext->codec_id);
    if (codecContext->codec == NULL)
    {
        av_free(frame);
        av_close_input_file(formatContext);
        std::cout << ""Couldn't find a proper decoder"" << std::endl;
        return 1;
    }
    else if (avcodec_open2(codecContext, codecContext->codec, NULL) != 0)
    {
        av_free(frame);
        av_close_input_file(formatContext);
        std::cout << ""Couldn't open the context with the decoder"" << std::endl;
        return 1;
    }

    AVPacket packet;
    av_init_packet(&packet);

    int packetCount = 0;
    int decodedFrameCount = 0;
    while (av_read_frame(formatContext, &packet) == 0)
    {
        ++packetCount;
        if (packet.stream_index == audioStream->index)
        {
            int frameFinished = 0;
            avcodec_decode_audio4(codecContext, frame, &frameFinished, &packet);

            if (frameFinished)
            {
                ++decodedFrameCount;
            }
        }

        av_free_packet(&packet);
    }

    std::cout << ""packetCount: "" << packetCount << ""\tdecodedFrameCount: "" << decodedFrameCount << std::endl;
    std::cout << ""formatContext->iformat->flags: "" << formatContext->iformat->flags << ""\tno byte seeking: "" << (formatContext->iformat->flags & AVFMT_NO_BYTE_SEEK) << std::endl;

    avcodec_flush_buffers(codecContext);
    av_init_packet(&packet);
    std::cout << ""av_seek_frame() returned: "" << av_seek_frame(formatContext, -1, 0, AVSEEK_FLAG_BYTE) << std::endl;
    
    packetCount = 0;
    decodedFrameCount = 0;
    while (av_read_frame(formatContext, &packet) == 0)
    {
        ++packetCount;
        if (packet.stream_index == audioStream->index)
        {
            // Try to decode the packet into a frame
            int frameFinished = 0;
            avcodec_decode_audio4(codecContext, frame, &frameFinished, &packet);

            if (frameFinished)
            {
                ++decodedFrameCount;
            }
        }

        av_free_packet(&packet);
    }

    std::cout << ""packetCount: "" << packetCount << ""\tdecodedFrameCount: "" << decodedFrameCount << std::endl;

    av_free(frame);
    avcodec_close(codecContext);
    av_close_input_file(formatContext);
}
}}}

'''Actual results:'''
{{{
packetCount: 526        decodedFrameCount: 259
formatContext->iformat->flags: 0        no byte seeking: 0
av_seek_frame() returned: 0
packetCount: 0  decodedFrameCount: 0
}}}

'''Expected results:''' (if seeking really does succeed)
{{{
packetCount: 526        decodedFrameCount: 259
formatContext->iformat->flags: 0        no byte seeking: 0
av_seek_frame() returned: 0
packetCount: 526        decodedFrameCount: 259
}}}

'''Alternative expected results:''' (if seeking really does fail because byte seeking is not allowed)
{{{
packetCount: 526        decodedFrameCount: 259
formatContext->iformat->flags: 32768        no byte seeking: 32768
av_seek_frame() returned: -1
packetCount: 0        decodedFrameCount: 0
}}}"	defect	closed	normal	avformat	git-master	fixed	seek				1	0