Re: [FFmpeg-devel] [PATCH 2/4] fftools/ffmpeg: stop using av_stream_get_parser()

[James Almer <jamrial@gmail.com>]

On 8/18/2022 10:58 AM, Andreas Rheinhardt wrote:
> Anton Khirnov:
>> The parser is internal to the demuxer, so its state at any particular
>> point is not well-defined for the caller. Additionally, it is being
>> accessed from the main thread, while demuxing runs in a separate thread.
>>
>> Use a separate parser owned by ffmpeg.c to retrieve the same
>> information.
>>
>> Fixes races, e.g. in:
>> - fate-h264-brokensps-2580
>> - fate-h264-extradata-reload
>> - fate-iv8-demux
>> - fate-m4v-cfr
>> - fate-m4v
>> ---
>>   fftools/ffmpeg.c     | 33 +++++++++++++++++++++++++++++++--
>>   fftools/ffmpeg.h     |  9 +++++++++
>>   fftools/ffmpeg_opt.c |  9 +++++++++
>>   3 files changed, 49 insertions(+), 2 deletions(-)
>>
>> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
>> index ef7177fc33..580df0443a 100644
>> --- a/fftools/ffmpeg.c
>> +++ b/fftools/ffmpeg.c
>> @@ -610,6 +610,9 @@ static void ffmpeg_cleanup(int ret)
>>           avcodec_free_context(&ist->dec_ctx);
>>           avcodec_parameters_free(&ist->par);
>>   
>> +        avcodec_free_context(&ist->parser_dec);
>> +        av_parser_close(ist->parser);
>> +
>>           av_freep(&input_streams[i]);
>>       }
>>   
>> @@ -2421,6 +2424,15 @@ static int process_input_packet(InputStream *ist, const AVPacket *pkt, int no_eo
>>           ret = av_packet_ref(avpkt, pkt);
>>           if (ret < 0)
>>               return ret;
>> +
>> +        if (ist->parser) {
>> +            // we do not use the parsed output, only the
>> +            // filled codec context fields
>> +            uint8_t *dummy;
>> +            int      dummy_size;
>> +            av_parser_parse2(ist->parser, ist->parser_dec, &dummy, &dummy_size,
>> +                             pkt->data, pkt->size, pkt->pts, pkt->dts, pkt->pos);
>> +        }
>>       }
>>   
>>       if (pkt && pkt->dts != AV_NOPTS_VALUE) {
>> @@ -2452,7 +2464,8 @@ static int process_input_packet(InputStream *ist, const AVPacket *pkt, int no_eo
>>                   if (pkt && pkt->duration) {
>>                       duration_dts = av_rescale_q(pkt->duration, ist->st->time_base, AV_TIME_BASE_Q);
>>                   } else if(ist->dec_ctx->framerate.num != 0 && ist->dec_ctx->framerate.den != 0) {
>> -                    int ticks= av_stream_get_parser(ist->st) ? av_stream_get_parser(ist->st)->repeat_pict+1 : ist->dec_ctx->ticks_per_frame;
>> +                    int ticks = ist->parser ? ist->parser->repeat_pict + 1 :
>> +                                              ist->dec_ctx->ticks_per_frame;
>>                       duration_dts = ((int64_t)AV_TIME_BASE *
>>                                       ist->dec_ctx->framerate.den * ticks) /
>>                                       ist->dec_ctx->framerate.num / ist->dec_ctx->ticks_per_frame;
>> @@ -2555,7 +2568,8 @@ static int process_input_packet(InputStream *ist, const AVPacket *pkt, int no_eo
>>               } else if (pkt->duration) {
>>                   ist->next_dts += av_rescale_q(pkt->duration, ist->st->time_base, AV_TIME_BASE_Q);
>>               } else if(ist->dec_ctx->framerate.num != 0) {
>> -                int ticks= av_stream_get_parser(ist->st) ? av_stream_get_parser(ist->st)->repeat_pict + 1 : ist->dec_ctx->ticks_per_frame;
>> +                int ticks = ist->parser ? ist->parser->repeat_pict + 1 :
>> +                                          ist->dec_ctx->ticks_per_frame;
>>                   ist->next_dts += ((int64_t)AV_TIME_BASE *
>>                                     ist->dec_ctx->framerate.den * ticks) /
>>                                     ist->dec_ctx->framerate.num / ist->dec_ctx->ticks_per_frame;
>> @@ -2688,6 +2702,21 @@ static int init_input_stream(int ist_index, char *error, int error_len)
>>           assert_avoptions(ist->decoder_opts);
>>       }
>>   
>> +    if (ist->parser) {
>> +        AVCodecParameters *par_tmp;
>> +
>> +        par_tmp = avcodec_parameters_alloc();
>> +        if (!par_tmp)
>> +            return AVERROR(ENOMEM);
>> +
>> +        ret = avcodec_parameters_from_context(par_tmp, ist->dec_ctx);
>> +        if (ret >= 0)
>> +            ret = avcodec_parameters_to_context(ist->parser_dec, par_tmp);
>> +        avcodec_parameters_free(&par_tmp);
>> +        if (ret < 0)
>> +            return ret;
>> +    }
>> +
>>       ist->next_pts = AV_NOPTS_VALUE;
>>       ist->next_dts = AV_NOPTS_VALUE;
>>   
>> diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
>> index 44cc23fa84..f67a2f1d1d 100644
>> --- a/fftools/ffmpeg.h
>> +++ b/fftools/ffmpeg.h
>> @@ -334,6 +334,15 @@ typedef struct InputStream {
>>       AVFrame *decoded_frame;
>>       AVPacket *pkt;
>>   
>> +    /**
>> +     * Parser for timestamp processing.
>> +     */
>> +    AVCodecParserContext *parser;
>> +    /**
>> +     * Codec context needed by parsing.
>> +     */
>> +    AVCodecContext       *parser_dec;
>> +
>>       int64_t       prev_pkt_pts;
>>       int64_t       start;     /* time when read started */
>>       /* predicted dts of the next packet read for this stream or (when there are
>> diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
>> index 30ca5cd609..a505c7b26f 100644
>> --- a/fftools/ffmpeg_opt.c
>> +++ b/fftools/ffmpeg_opt.c
>> @@ -1065,6 +1065,15 @@ static void add_input_streams(OptionsContext *o, AVFormatContext *ic)
>>               ist->top_field_first = -1;
>>               MATCH_PER_STREAM_OPT(top_field_first, i, ist->top_field_first, ic, st);
>>   
>> +            ist->parser = av_parser_init(ist->dec->id);
>> +            if (ist->parser) {
>> +                ist->parser->flags |= PARSER_FLAG_COMPLETE_FRAMES;
>> +
>> +                ist->parser_dec = avcodec_alloc_context3(NULL);
>> +                if (!ist->parser_dec)
>> +                    exit_program(1);
>> +            }
>> +
>>               break;
>>           case AVMEDIA_TYPE_AUDIO:
>>               ist->guess_layout_max = INT_MAX;
> 
> Are you aware that some parsers (e.g. the HEVC one) are still slow even
> with the PARSER_FLAG_COMPLETE_FRAMES flag and consume non-negligible
> amounts of memory?

Is it because it uses ff_h2645_packet_split()? It used to do like 
h264_parser and feature a custom NAL splitting implementation in order 
to not bother unscaping entire slice NALs (For raw annexb) since it only 
cares about their headers.

Maybe adding a max_read_size parameter to it so it stops parsing NALs 
after that point would help. It would also allow us to use it in 
h264_parser, simplifying it considerably.

> 
> - Andreas
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